study on the effectiveness of personal cooling equipment

“Study on the Effectiveness

of Personal Cooling Equipment

for Protecting Workers from Heat Stroke

while Working in a Hot Environment”

2013

Occupational Safety and Health Council

Study on the Effectiveness of Personal Cooling Equipment for Protecting Workers from Heat Stroke while Working in a Hot Environment

Occupational Safety and Health Council 1

Content Page

List of Tables .................................................................................................... 2

List of Figures .................................................................................................. 3

1. Introduction .................................................................................................. 4

2. Approach and Methodology ......................................................................... 5

3. Major activities undertaken .......................................................................... 6

4. Results ......................................................................................................... 8

4.1. Review and identification of two cooling vests ....................................... 8

4.2. Measuring the performance of cooling vests across four targeted

industries .................................................................................................... 11

4.2.1 Protocol of field study ..................................................................... 11

4.2.2 Record of field study ....................................................................... 12

4.2.3 Results of field study ....................................................................... 13

4.3 Summary of advantages and disadvantages of the personal cooling vests

under scrutiny ............................................................................................. 23

4.4. Determination of the cooling capacity of the selected cooling vest ...... 25

4.4.1 Protocol of treadmill running test inside a climatic chamber ........... 25

4.4.2 Records of treadmill running test .................................................... 27

4.4.3 Results of treadmill running test...................................................... 28

5. Recommendations ..................................................................................... 35

6. References ................................................................................................ 37

7. Appendices ................................................................................................ 41

Appendix A.................................................................................................. 41

Appendix B ................................................................................................. 43



List of Tables Page

Table 4.1.1 Basic information of the cooling vests .................................................................... 9

Table 4.2.1 Protocol of field study ............................................................................................ 12

Table 4.2.2 Record of field study ............................................................................................. 12

Table 4.2.3 Basic demographic information ............................................................................ 14

Table 4.2.4a Environmental data (Outdoor: construction, horticulture and cleaning, and airport

apron service industries) ......................................................................................................... 16

Table 4.2.4b Environmental data (Indoor: kitchen and catering industry) ............................... 16

Table 4.2.5 Physiological data ................................................................................................. 17

Table 4.2.6 Ratings of perceived exertion (RPE) .................................................................... 17

Table 4.2.7 Subjective assessments ....................................................................................... 18

Table 4.2.8a Percentage of construction workers who liked (rating '5' to '7' inclusive) Vest A vs

Vest B ...................................................................................................................................... 19

Table 4.2.8b Percentage of horticultural and cleaning workers who liked (rating '5' to '7' inclusive)

Vest A vs Vest B ....................................................................................................................... 20

Table 4.2.8c Percentage of airport apron service workers who liked (rating '5' to '7' inclusive)

Vest A vs Vest B ....................................................................................................................... 21

Table 4.2.8d Percentage of kitchen and catering workers who liked (rating '5' to '7' inclusive)

Vest A vs Vest B ....................................................................................................................... 21

Table 4.3.1 Advantages and disadvantages of Vest A and Vest B .......................................... 25

Table 4.4.1 Protocol of treadmill running test inside a climatic chamber................................. 26

Table 4.4.1a Intensity of treadmill running test ........................................................................ 27

Table 4.4.2 Record of treadmill running test ............................................................................ 28

Table 4.4.3 Descriptive statistics ............................................................................................. 29



List of Figures Page

Figure 3.1 Major activities undertaken ...................................................................................... 7

Figure 4.2.1 Number and percentage of participants distributed by occupations ................... 14

Figure 4.2.2a Number and percentage of participants distributed by construction trades ...... 14

Figure 4.2.2b Trade distribution of the horticulture and cleaning industry............................... 15

Figure 4.2.2c Trade distribution of the airport apron service industry ..................................... 15

Figure 4.2.2d Trade distribution of the kitchen and catering industry ...................................... 16

Figure 4.2.3 Perceived cooling effective time .......................................................................... 18

Figure 4.2.4 Percentages of workers who rated ‘5’ to ‘7’ (inclusive) on the attribute of ‘dislike-like’

to two cooling vests ................................................................................................................. 19

Figure 4.2.5 Factors affecting participants’ preferences ......................................................... 22

Figure 4.2.6 Summary of workers’ preference ........................................................................ 22

Figure 4.4.1 Scattered plots and linear curves of average Tc - with vs. without cooling vest

during exercise ........................................................................................................................ 30

Figure 4.4.2 Scattered plots and linear curves of average HR - with vs. without cooling vest

during exercise ........................................................................................................................ 31

Figure 4.4.3 Scattered plots and linear curves of average PSI - with vs. without cooling vest

during exercise ........................................................................................................................ 32

Figure 4.4.4 Scattered plots and linear curves of average Tc - with vs. without cooling vest

during recovery ........................................................................................................................ 33

Figure 4.4.5 Scattered plots and linear curves of average HR - with vs. without cooling vest

during recovery ........................................................................................................................ 34

Figure 4.4.6 Scattered plots and linear curves of average PSI - with vs. without cooling vest

during recovery ........................................................................................................................ 35



1. Introduction

Hong Kong is getting warmer because of climatic change. It was recorded that

the outdoor temperature and relative humidity in summer time can be as high

as 35.4 °C and 95% respectively (Hong Kong Observatory, 2012). Such hot

conditions in outdoor environments may have a serious negative effect, such as

dehydration, heat stroke, and elevated heart rate, on front-line workers

(Fogleman et al., 2005). To control human heat strain in hot environments, the

practical approach is to provide a personal clothing ensemble to build up a

cooler microclimate for auxiliary body cooling (Nunneley, 1970; Shvartz, 1972).

Different types of heat protective personalized clothing ensembles (e.g. ice vest,

air- or water cooled vests, frozen gel vest, wettable covers) have been

developed to conserve a comfortable microclimate. Previous studies (Pimental

et al., 1992; Bennett et al., 1995; Webster et al., 2005; Choi et al., 2008; Hadid

et al., 2008) have showed that properly designed cooling vests were effective at

alleviating workers’ thermal strain when working in a hot weather.

In order to examine the effectiveness of various types of personal clothing

ensemble, OSHC commissioned the Kansas State University to test a number

of commercially available personal cooling products that are commonly used in

Hong Kong. Two cooling vests were identified for further on-site qualitative

comfort and usability assessments. The aim of these field studies is to conduct

qualitative comfort and usability assessment on the two types of personal

cooling vest. Front-line workers in four industries, including (1) construction, (2)

horticulture and outdoor cleaning, (3) airport apron, and (4) catering and kitchen

were selected to wear and assess the cooling vests. The key objectives of the

project are to:

(i) Conduct a survey to review and identify the types of personal

cooling products which are commonly used in Hong Kong for the

occupations/industries which require routine exposures of a

worker in a hot environment.

(ii) Determine the cooling performance of commercially available

phase change cooling vest (personal cooling equipment) under

different workloads and extreme temperature conditions and

evaluate the recovery rates such as recovery time, reduction in

core body temperature, and/or reduction in heart rate, etc

associated with the use of personal cooling equipment following

heat exposure while performing physical work.

(iii) Conduct physiological testing for measuring the performance

of personal cooling equipment and field research for FOUR



target industry subjects including (a) construction workers, (b)

catering and kitchen workers, (c) horticulture workers and

outdoor cleansing workers, and (d) airport apron workers (e.g.

ramp handling workers).

(iv) Provide performance assessment using human subjects

while performing the task in a hot work environment under

different workloads.

(v) Summarize the advantages and disadvantages of the

personal cooling equipment.

(vi) Recommend the suitability and applicability of the personal

cooling equipment in the respective operations or industries.

2. Approach and Methodology

A combination of research methods including literature review, qualitative

studies, and quantitative studies were applied in delivering the project.

Literature review and fact finding. The literature relating to

different types of personal cooling products that is commonly

used in Hong Kong for the occupations/industries which require

routine exposures of a worker in a hot environment were

comprehensively reviewed. Extensive literature review also

acquires information on the advantages and disadvantages of the

targeted personal cooling equipment.

Performance assessment. Both qualitative comfort and usability

assessment and quantitative physiological responses

assessment were conducted on-sites and inside a climatic

chamber respectively.

Validation and recommendation. Recommendations were drawn

after the results were validated.



3. Major activities undertaken

Major activities were undertaken by the research team from June 2012 to June

2013 as shown in Figure 3.1. After the commencement of the project, the

research team began to review and identify the commonly used personal

cooling products in Hong Kong for the occupations/industries and to design the

protocols for the field study and treadmill running tests inside a climatic

chamber. Briefing meetings with the main stakeholders of the four selected

industries were held to explain the rationale of the project and to recruit

front-line workers to voluntarily participate in the field study. Between August

2012 and January 2013, twelve field studies were conducted in four industries

(three in each industry), namely, the construction, horticulture and cleaning, and

airport apron service, and kitchen and catering industries to ascertain front-line

workers’ preference for a cooling vest qualitatively. Treadmill running tests

inside a climatic chamber were conducted from November 2012 to April 2013 to

assess the performance of the preferred cooling vest quantitatively. Data

collected were analyzed between April and May. Results and recommendations

were summarized in the final report which was submitted to OSHC in June

2013.

In addition, the research team had submitted two Progress Reports to OSHC’s

Project Monitoring Committee in September 2012 and November 2012

respectively.



Figure 3.1 Major activities undertaken

Project Commencement Date: 1 July, 2012 Project Completion Date: 30 June 2013

TASKS

MONTH / FORTNIGHT

JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

1. Regular Meetings with the OSHC’s

Project Monitoring Committee

2. Review and Identify Common PCE

3. Sourcing and Delivery of Selected

PCE

4. Design of Experimental Protocol

Extensive literature review

Design of quantitative assessments

Design of qualitative assessments

Recruitment of volunteer participants

5. Field Study

6. Data Analysis

7. Study in Environmental Chamber

8. Evaluation of the tested PCE

9. Recommendation of PCE in the

Respective Operations

10. Interim Progress Report

11. Final Detailed Report

Legends

Milestone dates of submitting respective consultancy reports to OSHC

PCE = Personal Cooling Equipment



4. Results

4.1. Review and identification of two cooling vests

There are three main types of cooling systems: active, passive and combo

(combine the active and passive methods) (Chi et al., 2008). Active cooling

systems include external connections to air or liquid supplies such as

ventilated cooled air cooling (Shapiro et al., 1982; Pimental et al., 1987;

Kuklane et al., 2000) and circulated liquid cooling (Shapiro et al., 1982;

Pimental et al., 1988; Jetté, 2004) or without external connections such as a

battery driven ambient air fan based garment (Shapiro et al.,1982; Hadid et al.,

2008). Active cooling has the ability to reduce both the cardiovascular and

thermoregulatory strain (Selkirk et al., 2004). Passive cooling systems utilize

phase change materials (e.g. ice, frozen gel, salt, paraffin, etc.) in vests and

clothing (Bennett et al., 1995; Webster et al., 2005; Carter et al., 2007; Choi et

al., 2008; Chou et al., 2008; Reinertsen et al., 2008). Phase change materials

as the heat exchange mediums (Yu-Tsuan et al., 2000), are characterized by

their ability to absorb energy when they change from a solid to a liquid state

and to release heat as they return to the solid phase (Reinertsen et al., 2008).

Frozen gel has been demonstrated to be effective in reducing thermal strain

(Bennett et al., 1995; Choi et al., 2008) and enhancing endurance (Webster et

al., 2005). Researches on personal cooling equipment have been widely

discussed in military, fire-fighting, sports and a few industries (such as the

power industry and agriculture) (e.g. Pimental & Avellini, 1992; Chou et al.,

2008; Webster et al., 2005; Furtado et al., 2007; Choi et al., 2008).

The Occupational Safety and Health Council had sourced two cooling vests,

Vest A and Vest B, which had been tested using a thermal manikin under 35 °C

and 65% relative humidity by the Kansas State University[1]. Basic information

of two cooling vests is listed in Table 4.1.1.

Vest A, as a kind of passive cooling vests, has been demonstrated useful for

reducing heat stress to soldiers (Pimental & Avellini, 1989; Pimental et al.,

1990; Pimental & Avellini, 1992). It consists of a vest and four strips of three

phase change packs. The fabric of Vest A is made of flame retardant cotton

fabric which is durable and washable. It has four side tabs and adjuster clips to

assure a good fit for all sizes. Body heat is absorbed by frozen gel

Thermo-strips™ which are inserted into the cooling vest. The non-toxic and

[1] McCullough E.A., Evaluation of Personal Cooling Systems Using a Thermal Manikin – Part II, Technical Report #12-210. Institute for Environmental Research, Kansas State University, Manhattan.



non-flammable frozen gel has high latent heat capacity (water based), which

can be repeatedly frozen/melted without degradation [2]. Total weight including

the garment and frozen gel pads reaches to about 2.3 kg. The effective cooling

time reported by Kansas’ report is about 65 minutes.

Vest B has a combo system combining passive and active cooling methods. It

has two quiet but fairly strong and detachable fans mounted in the back of the

vest. The power of the fan is adjustable. It has the option of using three gel

packs when the temperature is very hot. The non-toxic and non-flammable gel

packs can be directly used after soaking into the water or being frozen [3]. The

ultramarine fabric is thin and non-flammable. Total weight including the vest,

three frozen gel pads, and two fans with batteries is around 1 kg. The effective

cooling time reported by Kansas’ report is more than 120 minutes.

Table 4.1.1 Basic information of the cooling vests

Basic information Vest A Vest B

Type of cooling system Passive

Air circulation combined with

phase change material

packs[4]

Appearance

Distribution of gel pads

and/or fans on the vest

Composition A vest with 4 strips of 3

phase change packs

A vest with 3 pieces of gel

sets and 2 fans

Colour Khaki Ultramarine

Size One size fits all;

Unisex style

XL, and XXL;

Unisex style

[2] Source: Product specification. Available on line [URL]: http://www.steelevest.com/?page=Industrial_L.htm [3] Source: Product specification (In Korean). [4] Source: Kansas’s testing report. McCullough (2012) Evaluation of Personal Cooling Systems Using a Thermal Manikin – Part II.

http://www.steelevest.com/?page=Industrial_L.htm



Property of fabric Fire-resistant[5] Non-flammable[6]

Property of ice pad

• Jelly like ice pads

(made of gel and

water);

• Non-toxic,

non-flammable[7];

• Repeatedly frozen/

melted without

degradation[8];

• frozen at ~ -10°C [9]

• Jelly like ice pads (made

of gel and water);

• Non-toxic,

non-flammable[10];

• frozen at ~ -10°C[11]

Property of fan N/A

• Allow both high and low

speed;

• Require total four 1.5V

AA alkaline batteries or

1.2V AA rechargeable

batteries

• Detachable[12]

Area of each frozen gel pad (cm2) 419.87[13] 163.06

Weight of each frozen gel pad (kg) 0.41 0.12

Freezing time of gel pad No official statement[14] 4 hours or above[15]

Weight of garment (kg) 0.58 0.50 (XL)/0.51 (XXL)

Total weight (including frozen gel pads

and/or batteries) kg 2.3 1.02 (XL)/1.04 (XXL)

[5] Source: Product specification. Available online http://www.steelevest.com/?page=Industrial%5FL%2Ehtm [6] Source: Specification of the components of the fabrics. Provided by the Occupational Safety and Health Council. [7] Source: Specification of the components of gel packs. Provided by the Occupational Safety and Health Council. [8] Source: Product specification. Available online: http://www.steelevest.com/?page=Industrial%5FL%2Ehtm [9] Source: A document named “Personal cooling products for testing 2012 with spec to PolyU”. Provided by the Occupational Safety and Health Council. [10] Source: Specification of the components of gel packs. Provided by the Occupational Safety and Health Council. [11] Source: A document named “Personal cooling products for testing 2012 with spec to PolyU”. Provided by the Occupational Safety and Health Council. [12] Source: Product specification (In Korean). [13] The area and the weight of the gel pack were measured in the laboratory by the research team. [14] According to the experience of the research team, the freezing time of the gel packs requires at least six hours. [15] Source: A document named “Personal cooling products for testing 2012 with spec to PolyU”. Provided by the Occupational Safety and Health Council.

http://www.steelevest.com/?page=Industrial%5FL%2Ehtm

http://www.steelevest.com/?page=Industrial%5FL%2Ehtm



Effective cooling duration according to

Kansas’s testing report ~65 min 120 min

Cleaning method Machine washable and

dryable[16]

Hand wash and air-dry[17] or

Machine washable at 30℃ [18]

4.2. Measuring the performance of cooling vests across the four targeted

industries

4.2.1 Protocol of field study

Twelve field studies were conducted in four industries (three in each industry),

namely, the construction, horticulture, airport apron service, and kitchen and

catering industries, to gather the assessment data between August 2012 and

January 2013. Table 4.2.1 illustrates the protocol of field study. A maximum of

twelve healthy workers were invited to participate in each field study. In

general, every participant was asked randomly to wear the two types of

personal cooling vest, one in the morning, and one in the afternoon. Before

taking the first wear trial, the participants were briefed by a member of the

research team regarding the nature, purpose and method of the study. If they

raised no concerns, they were asked to sign a consent form approved by the

Human Subjects Ethics Sub-committee of The Hong Kong Polytechnic

University. Some basic demographic details, such as name, age, height,

weight, work trade, and years of experience in the related industries were

collected from the participants by means of a self-administered questionnaire.

Basic physiological data, such as ear temperature, pulse and blood pressure

were also monitored and recorded before and after each wear trial. While the

workers were undertaking the wear trial and performing their usual work

routines, environmental data including wet bulb and dry bulb temperatures,

globe temperature, relative humidity, wind speed, and barometric pressure

were collected continuously throughout the whole wear trail period via a Heat

Stress Monitor (QUESTemp° 36™, Australia). A questionnaire survey

assessing 18 subjective attributes towards the tested cooling vest was

administered immediately after each wear trial. Opinions regarding comfort,

suitability, practicality, acceptability, safety and other aspects of the tested

cooling vest were solicited. The participants were also asked to indicate the

Perceived Level of Exertion Scale (RPE) (McGuigan and Foster, 2004) which

was defined as the intensity of subjective effort, stress, or discomfort felt during

[16] Source: Product specification (In English): SteeleVest P/N SA1140 (Six Pocket) and SA440 (FOUR POCKET). [17] Source: Product specification (In Korean). [18] Source: Product label in the vest (In Korean).



physical activity (rating from 0=rest to 10=maximal effort) and give their

comments on the cooling vest. Furthermore, the participants were asked to

choose a preferred cooling vest after they completed both wear trials.

Appendix A attaches the figures of the equipment for collecting the

physiological and environmental data and a copy of blank questionnaire.

Table 4.2.1 Protocol of field study

Time Task

0800 Arrive at the field.

0800-0815 Preparation.

0815-0830 Explanation of study to the involved workers.

0830-0900 Basic personal information, fill in questionnaire (pre-test) and RPE; collect

physiological data such as ear temperature, blood pressure and pulse.

0900-1100 6 workers wear cooling Vest A while 6 workers wear Vest B. On-site

environmental data collection by heat stress monitor.

1100-1130 Fill in questionnaire (post-test1) and RPE; and collect physiological data

such as ear temperature, blood pressure and pulse.

1130-1200 Buffer time for emergency.

1200-1300 Lunch.

1300-1330 Buffer time after lunch and collect physiological data as in the morning.

1330-1530 12 workers change the types of cooling vest they wore in the first wear

trial. And the order of the cooling vest is counterbalanced on alternative

days to offset the sequential effect. On-site environmental data collection

by heat stress monitor.

1530-1600 Fill in questionnaire (post-test2) and RPE; and collect physiological data

as in the morning.

1600 Done.

4.2.2 Record of field study

Table 4.2.2 shows the basic information of each field study, including

occupation, date, company name and number of data set obtained. In total 130

workers participated in field studies, and 240 sets of data were obtained from

these field studies.

Table 4.2.2 Record of field study

Industry Date of Field

Study Company name and Site

No. of data set obtained

(morning + afternoon)

Construction 3 August 2012

(Fri)

Sanfield Building Contractors

Limited 24 (12 + 12)



7 August 2012

(Tue)

Sanfield Building Contractors

Limited 21 (12 + 9)

23 August 2012

(Thu) Gammon Construction Limited 24 (12 + 12)

Horticulture

and outdoor

cleaning

14 August 2012

(Tue)

Hong Yip Service Company

Limited & Hong Chui Landscape

Company Limited

21 (12 + 9)

28 August 2012

(Tue)

Hong Yip Service Company

Limited & Hong Chui Landscape

Company Limited

18 (9 + 9)

14 Sept 2012 (Fri) Sino Estates Management

Limited 24 (12 + 12)

Airport apron

service

4 Sept 2012 (Tue) Jardine Aviation Services Limited

(Hong Kong Airport) 24 (12 + 12)

10 Sept 2012

(Mon)

Sats Gateway HK Limited (Hong

Kong Airport) 24 (12 + 12)

24 Sept 2012

(Mon)

Hong Kong Airport Services

Limited (Hong Kong Airport) 24 (12 + 12)

Catering and

kitchen

11 Oct. 2012 (Thu) PolyU's staff canteen, Maxim's

Group 2 (1 + 1)

12 Nov. 2012

(Mon)

PolyU's student canteen, Maxim's

Group 24 (12 + 12)

7 Jan. 2012 (Mon) Tao Miao Institute, Tao Heung

Group 10 (5 + 5)

4.2.3 Results of field study

Basic demographic information is shown in Table 4.2.3. The average age of

the participants was 44, ranged from 18 to 70. The average height was 167 cm,

ranged from 142 to 196 cm. The average weight was 66 kg, ranged from 44 to

111 kg. The average working experience in the related industries was 11 years,

ranged from 0 to 35 years. Among the 130 participants, 36 were female and

the rest were male. Six workers were non-Chinese who came from Nepal and

Philippines, while the others were local. Moreover, 20 were indoor workers,

110 were outdoor workers. Numbers of participants distributed by four

industries are depicted in Figure 4.2.1. Figures 4.2.2a-4.2.2d illustrate the

trade distribution of each industry.



Table 4.2.3 Basic demographic information

Item Mean±SD Range

Age 44 ± 12.46 18-70

Height (cm) 167 ± 8.65 142-196

Weight (kg) 66 ± 11.14 44-111

Working experience in the

related industries (year)

11 ± 9.94 0-35

Figure 4.2.1 Number and percentage of participants distributed by occupations

Figure 4.2.2a Number and percentage of participants distributed by construction trades

36 (27.69%)

33 (25.38%)

43 (33.08%)

18 (13.85%)

Constructionworkers

Horticulturaland cleaningworkers

Airport apronserviceworkers

Kitchen andcateringworkers

3 (8.33%)

8 (22.22%)

6 (16.67%)

1 (2.78%)

5 (13.89%)

8 (22.22%)

1 (2.78%)

1 (2.78%)

1 (2.78%)

2 (5.56%)

0 2 4 6 8 10

Other workers

Handyman

Drainlayer and Plumber

Leveller

Form worker

Fixer

Welder

Cladding worker

Technician

Foreman

Number and percentage



Figure 4.2.2b Trade distribution of the horticulture and cleaning industry

Figure 4.2.2c Trade distribution of the airport apron service industry

9 (27.27%)

20 (60.61%)

4 (12.12%)

Horticultural worker

Cleaning worker

Other workers

18 (41.86%)

7 (16.28%)

3 (6.98%)1 (2.33%)

6 (13.95%)8 (18.60%)

02468

101214161820




Figure 4.2.2d Trade distribution of the kitchen and catering industry

Environmental data (outdoor) and (indoor) of the field studies are shown in

Table 4.2.4a and Table 4.2.4b respectively. The mean outdoor WBGT is 31.11

± 3.24 (°C), and the mean outdoor relative humidity is 54.73 ± 14.99 (%). The

mean indoor WBGT is 23.72 ± 2.93 (°C), and the mean indoor relative humidity

is 65.14 ± 7.27 (%).

Table 4.2.4a Environmental data (Outdoor: construction, horticulture and cleaning, and

airport apron service industries)

Index Mean ± SD Range

Natural wet bulb temperature (°C) 27.99 ± 2.78 19.79 ~ 38.17

Dry bulb temperature (°C) 32.48 ± 2.97 20.52 ~ 38.70

Globe thermometer temperature (°C) 41.14 ± 7.39 20.95 ~ 54.52

Relative humidity (%) 54.70 ± 14.94 31 ~ 89

Wet bulb globe temperature index (Out) (°C) 31.11 ± 3.24 20.11 ~ 40.11

Heat index 37.23 ± 3.95 20.40~ 54.40

Wind speed in meter per second (m/s) 1.21 ± 1.12 0.07 ~ 12.13

Table 4.2.4b Environmental data (Indoor: kitchen and catering industry)

Index Mean ± SD Range

Natural wet bulb temperature (°C) 22.07 ± 2.91 15.53 ~ 25.39

Dry bulb temperature (°C) 26.89 ± 3.16 20.11 ~ 30.22

Globe thermometer temperature (°C) 27.56 ± 3.09 20.35 ~ 30.58

Relative humidity (%) 65.14 ± 7.27 44 ~ 87

Wet bulb globe temperature index (In) (°C) 23.72 ± 2.93 17.06 ~ 26.69

Heat index 30.61 ± 3.66 20.5 ~ 37

Wind speed in meter per second (m/s) 0.28 ± 0.13 0.02 ~ 1.08

3 (16.7%) 3 (16.7%) 3 (16.7%)

1 (5.6%) 1 (5.6%)

3 (16.7%)

4 (22.2%)

0

1

2

3

4

5

Chinesedessert

BBQ Cooking Frying Boiling Furnaceend

Other




Measurements of core temperature (Tc), heart rate (HR), systolic blood

pressure (SBP) and diastolic blood pressure (DBP) before and after wear trials

are shown in Table 4.2.5. No significant differences of physiological responses

were observed between the two types of cooling vest.

Table 4.2.5 Physiological data

Type

Tc

before

test

(°C)

HR

before

test

(bpm)

SBP

before

test

(mmHg)

DBP

before

test

(mmHg)

Tc

after

test

(°C)

HR

after

test

(bpm)

SBP

after

test

(mmHg)

DBP

after

test

(mmHg)

Vest A Mean 36.08 78 130 84 36.38 81 132 89

SD 0.55 13.32 15.33 12.40 0.62 16.08 16.22 15.52

Vest B Mean 36.14 77 132 87 36.34 80 134 89

SD 0.48 11.24 17.52 15.54 0.68 12.49 17.56 16.76

RPE is shown in Table 4.2.6. The values were almost identical for both types of

cooling vests before working. However, the participants felt moderate exertion

for Vest B (3.8) and somewhat harder exertion for Vest A (4.58) after working.

Table 4.2.6 Ratings of perceived exertion (RPE)

Type

RPE before test RPE after test

Vest A Mean 2.13 4.58

SD 1.01 1.80

Vest B Mean 2.12 3.80

SD 1.06 1.57

The perceived effective cooling times were almost identical for both types of

cooling vests. The effective cooling time for wearing the cooling vest is shown

in Figure 4.2.3. The effective cooling time is 1.28 ± 0.54 hrs and 1.34 ± 0.58

hrs for Vest A and Vest B respectively.



Figure 4.2.3 Perceived cooling effective time

Mean values of the subjective assessments are shown in Table 4.2.7. In

general, Vest B was rated higher than that of Vest A (4.26 ± 2.11 vs. 2.79 ±

1.88). The differences among the subjective values between two cooling vests

were tested by ANOVA. The significance level was set at p<0.05. Most

subjective attributes had significant differences between two cooling vests,

except ‘prickle – non prickle’ and ‘itchy – non itchy’.

Table 4.2.7 Subjective assessments

Subjective Responses Vest A

(Mean ± SD)

Vest B

(Mean ± SD) p-value

Clammy---Dry 3.50 ± 1.78 4.54 ± 1.81 <0.001

Sticky---Non- adhesive 4.26 ± 2.04 4.85 ±1.88 <0.05

Air tight---Breathable 3.36 ± 1.80 4.00 ± 2.01 <0.05

Damp---Dry 2.68 ±1.85 4.20 ± 1.99 <0.001

Heavy---Light 1.92 ± 1.29 4.75 ± 1.86 <0.001

Hot---Cool 4.28 ± 1.90 3.81 ± 1.71 <0.05

Scratchy---Non-scratchy 5.51 ± 1.79 6.02 ± 1.22 <0.05

Prickle---Non-prickle 5.96 ±1.56 6.12 ± 1.24 -

Itchy---Non-itchy 6.00 ± 1.61 6.02 ± 1.52 -

Rough---Smooth 4.13 ± 1.92 5.88 ± 1.36 <0.001

Stiff---Pliable 2.80 ±1.66 5.80 ± 1.39 <0.001

Movement restricted---

Movement allowed 2.97 ± 1.76 4.73 ± 1.95

<0.001

Tight---Loose 3.61 ± 1.62 4.51 ± 1.83 <0.001

Uncomfortable---Comfortable 3.06 ± 1.85 4.45 ± 1.87 <0.001

Impractical---Practical 3.06 ± 1.97 4.02 ± 2.02 <0.001

Job performance

interference---No job 3.40 ± 2.06 4.57 ± 2.02

<0.001

1.281.34

0.5

1

1.5

2

Vest A Vest B

Tim

e (

ho

ur)

Type

Perceived cooling effective time



performance interference

Unsafe---Safe 5.05 ± 1.72 5.52 ± 1.71 <0.05

Dislike---Like 2.79 ±1.88 4.26 ± 2.11 <0.001

Figure 4.2.4 depicts the percentages of different industries’ workers who rated

‘5’ to ‘7’ (inclusive) on the attribute of ‘dislike-like’ to two cooling vests.

Subjective preference of all industries workers for Vest B was rated higher than

that of Vest A. In the construction industry, the percentage of workers who

rated ‘5’ to ‘7’ (inclusive) on the attribute of ‘dislike-like’ to Vest B was 38.89 %,

which was more than that of Vest A (15.15 %). In the horticulture and cleaning

industry, the percentage of workers who rated ‘5’ to ‘7’ (inclusive) on the

attribute of ‘dislike-like’ to Vest B was 59.38 %, while that to Vest A was

29.03 %. In the airport apron service industry, the percentage of workers who

rated ‘5’ to ‘7’ (inclusive) on the attribute of ‘dislike-like’ to Vest B and Vest A

was 43.24 % and 27.78 % respectively. In the kitchen and catering industry,

the percentage of workers who rated ‘5’ to ‘7’ (inclusive) on the attribute of

‘dislike-like’ to Vest B was 61.11%, which was a lot higher than that to Vest A

(5.56 %). Table 4.2.8a – 4.2.8d show the percentages of each attribute rated ‘5’

to ‘7’ (inclusive) by workers of four industries respectively.

Figure 4.2.4 Percentages of workers who rated ‘5’ to ‘7’ (inclusive) on the attribute of

‘dislike-like’ to two cooling vests

Table 4.2.8a Percentage of construction workers who liked (rating '5' to '7' inclusive)

Vest A vs Vest B

Subjective responses Vest A Vest B

Clammy-Dry 21.88 (7/32) 36.11 (13/36)

Sticky-Non adhesive 58.06 (18/31) 44.44 (16/36)

Air tight-Breathable 15.63 (5/32) 27.78 (10/36)

Damp-Dry 9.09 (3/33) 36.11 (13/36)

Heavy-Light 6.25 (2/32) 44.44 (16/36)

15.15%

29.03% 27.78%

5.56%

38.89%

59.38%

43.24%

61.11%

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

Constructionindustry

Horticultureand cleaning

industry

Airport apronserviceindustry

Kitchen andcateringindustry

Vest A Vest B



Hot-Cool 37.50 (12/32) 30.56 (11/36)

Scratchy-Non scratchy 81.82 (27/33) 83.33 (30/36)

Prickle-Non prickle 90.91 (30/33) 86.11 (31/36)

Itchy-Non itchy 90.91 (30/33) 83.33 (30/36)

Rough-Smooth 36.36 (12/33) 86.11 (31/36)

Stiff-Pliable 9.09 (3/33) 75 (27/36)

Movement allowed – Movement

restricted

21.88 (7/32) 65.71 (23/35)

Tight-Loose 21.88 (7/32) 41.67 (15/36)

Uncomfortable-Comfortable 15.15 (5/33) 50 (18/36)

Impractical-Practical 18.18 (6/33) 38.89 (14/36)

Interfere job performance- Not

interfere job performance

27.27 (9/33) 55.56 (20/36)

Unsafe-Safe 60.61 (20/33) 80.56 (29/36)

Dislike-Like 15.15 (5/33) 38.89 (14/36)

Table 4.2.8b Percentage of horticultural and cleaning workers who liked (rating '5' to '7'

inclusive) Vest A vs Vest B


Clammy-Dry 22.58 (7/31) 68.75 (22/32)



Damp-Dry 16.67 (5/30) 64.52 (20/31)

Heavy-Light 0.00 (0/31) 65.63 (21/31)

Hot-Cool 38.71 (12/31) 36.67 (11/30)



Itchy-Non itchy 90.32 (28/31) 87.50 (28/32)

Rough-Smooth 41.94 (13/31) 87.10 (27/31)

Stiff-Pliable 9.68 (3/31) 93.75 (30/32)


restricted

19.35 (6/31) 61.29 (19/31)

Tight-Loose 25.81 (8/31) 22/32 (68.75)

Uncomfortable-Comfortable 41.94 (13/31) 54.84 (17/31)




38.71 (12/31) 54.84 (17/31)

Unsafe-Safe 67.74 (21/31) 84.38 (27/32)

Dislike-Like 29.03 (9/31) 59.38 (19/32)



Table 4.2.8c Percentage of airport apron service workers who liked (rating '5' to '7'



Clammy-Dry 31.43 (11/35) 48.65 (18/37)



Damp-Dry 16.67 (6/36) 36.11 (13/36)

Heavy-Light 8.33 (3/36) 54.05 (20/37)

Hot-Cool 47.22 (17/36) 30.56 (11/36)



Itchy-Non itchy 61.11 (22/36) 75.68 (28/37)

Rough-Smooth 36.11 (13/36) 69.44 (25/36)

Stiff-Pliable 22.22 (8/36) 67.57 (25/37)


restricted

27.78 (10/36) 45.95 (17/37)

Tight-Loose 19.44 (7/36) 40.54 (15/37)





30.56 (11/36) 45.95 (17/37)

Unsafe-Safe 55.56 (20/36) 59.46 (22/37)

Dislike-Like 27.78 (10/36) 43.24 (16/37)

Table 4.2.8d Percentage of kitchen and catering workers who liked (rating '5' to '7'



Clammy-Dry 50.00 (9/18) 83.33 (15/18)



Damp-Dry 33.33 (6/18) 66.67 (12/18)

Heavy-Light 0.00 (0/18) 88.89 (16/18)

Hot-Cool 77.78 (14/18) 66.67 (12/18)



Itchy-Non itchy 94.44 (17/18) 100.00 (18/18)

Rough-Smooth 50.00 (9/18) 100.00 (18/18)

Stiff-Pliable 11.11 (2/18) 100.00 (18/18)


restricted

11.11 (2/18) 66.67 (12/18)

Tight-Loose 11.11 (2/18) 66.67 (12/18)







11.11 (2/18) 66.67 (12/18)

Unsafe-Safe 55.56 (10/18) 66.67 (12/18)

Dislike-Like 5.56 (1/18) 61.11 (11/18)

Factor analysis was used to explore the underlying factors between the 17

items of subjective attributes (all except ‘dislike-like’). Figure 4.2.5 illustrates

that four factors will affect workers’ preference on cooling vest. These are:

thermal comfort, usability, tactile comfort, and fabric hand (feel).

Thermal comfort

clammy – dry

sticky – non adhesive

air tight – breathable

damp – dry

hot – cool

Usability

job performance interference – No job

performance interference

tight – loose

impractical – practical

uncomfortable – comfortable

unsafe – safe

Tactile comfort

scratchy – non scratchy

prickle – non prickle

itchy – non itchy

Fabric hand (feel)

heavy – light

rough – smooth

stiff – pliable

movement restricted – movement allowed

Figure 4.2.5 Factors affecting participants’ preferences

Figure 4.2.6 shows that 26 workers preferred Vest A and 83 workers preferred

Vest B, while 2 workers preferred neither Vest A nor Vest B. With the approval

from the OSHC, Vest B was chosen to be further evaluated quantitatively in a

climatic chamber.

Figure 4.2.6 Summary of workers’ preference

26

83

2

0

10

20

30

40

50

60

70

80

90

Vest A Vest B Neither

Nu

mb

er

Type

Preference

Personal

preference:

Dislike-Like



4.3 Summary of advantages and disadvantages of the personal cooling

vests under scrutiny

Based on the results of field studies, particularly the comments given by the

participants, the strengths and shortcomings are summarized in Table 4.3.1.

Among the 105 participants who commented on Vest A, 23.8 % of them stated

that Vest A had effective cooling effect, while 4.76 % of them thought it was

somewhat effective. 5.71 % of them considered that it could reduce their

temperature, and 9.5 % of the participants felt it was cool during wear trials.

Only 2.9 % of them agreed that it was comfortable. Vest A was considered

aesthetic by 1.9 % of the participants. Moreover, the advantage of fire-resistant

fabric of Vest A made welders, airport apron service workers and kitchen and

catering workers feel assured against fire risk during wear trials.

However, the shortcomings and problems of Vest A were manifest. Results of

subjective assessments reported that Vest A had thermal discomfort, poor

hand feel and poor usability because the average ratings of all attributes of

thermal comfort factor, fabric hand (feel) and usability (except “unsafe-safe”)

by all workers were just four or below. Uncomfortable hand and tactile feel was

one of the major problems of Vest A. Nearly 52.4 % of the 105 participants

considered that it was too heavy and bulky (42.9 %), thick (1.9 %), rough

(0.9 %), prickle (4.8 %), and scratchy (1.9 %). 51.4 % of the participants

complained about thermal discomfort caused by Vest A, including airtightness

(9.5 %), dampness (25.7 %), sticky (1.9 %) and chilly feelings (14.3 %). The

cooling effect of vest A might decrease local skin temperature too much and

thus cause discomfort (Yoshimi et al. 1998). Poor usability was also an obvious

shortcoming for Vest A. About 41 % of the participants stated it was

uncomfortable (18.1 %), impractical (2.9 %), misfit (4.8 %), movement

restricted (5.7 %), and it interfered work (9.5 %). 26.7 % of the participants

perceived that the cooling capacity of Vest A was temporary and partial. For

instance, the cooling effect lasted for only half to one and a half hours because

ice melted quickly, which echoed the Kansas’ report on Vest A that it was most

effective during the first hour of use and Shim et al. (2001) and Wan & Fan

(2009) who reported that microcapsules of phase change materials in clothing

provided a small, temporal cooling effect during environmental transients.

Some participants pointed out that it was only effective during rest rather than

working period, or only effective on those parts of body covered by the frozen

gel pads. Nine and a half percent of the participants had uncomfortable

symptoms such as ache, dizziness, and discomfort on heart and stomach and

0.9 % of them worried about whether they would get rheumatism if they wear



Vest A.

The ratings of all subjective attributes on Vest B were at four or above, which

implied that it had better thermal comfort (except “hot-cool”), fabric hand feel,

tactile comfort and usability than Vest A. Among 106 participants who gave

comments on Vest B, 16.2 % of them stated it was effective, while 13.3 % of

them thought it was somewhat effective. Cool feeling from two fans (15.1 %)

and comfortable perceptions (9.4 %) were the major reported advantages.

Other strengths such as dryness, thinness, and lightness (6.6 %), collectively

made it more acceptable and satisfied by the participants.

However, Vest B is not without disadvantages. The major shortcoming of Vest

B was the limited cooling capacity perceived by the participants (40.6 %). Most

participants could not feel the cooling effect when they worked under direct

sunlight or with high workloads. The sense of cooling was insufficient because

of the limited amount of phase change materials and covering area (Choi et al.,

2008; Gao et al., 2010) where the upper part of the body, the neck and the

head still felt hot during wear trials. Thirty-one percent of the participants

complained that it had poor thermal comfort. For instance, the dark colour

absorbed much heat from the surrounding hot environment (4.7 %). Thermal

discomfort also included dampness (6.6 %), airtight (12.3 %), hot outdoor

(4.7 %) and chilly indoor (2.8 %). Some participants also stated that Vest B

was impractical (2.8 %), misfit (4.7 %), and impeding works by adding

workload (6.6 %). Some participants considered that it was inconvenient to use

because of the non-durable fabric (1.9 %) and noisy fans (1.9 %). Moreover,

the fans could induce discomfort to the waist and blow hot air from surrounding

environment (12.3 %). About two percent of the participants were also

concerned about the potential safety hazards of the fabric and electronic fan.

Furthermore, Vest B had two distinct shortcomings. First, using common

alkaline batteries was not environmental friendly, while using rechargeable

batteries required a lengthy charge-up time and was unreliable. Second, Vest

B had to be washed by hand and air-dried, which was also time consuming

and labour intensive.



Table 4.3.1 Advantages and disadvantages of Vest A and Vest B

Type Advantages Disadvantages

Vest A Effective in cooling down

temperature

Limited (temporary and

partly) cooling capacity

Fire-resistant Thermal discomfort

Aesthetic Heavy and other

uncomfortable hand and

tactile feel

Poor usability

Potential health problems

Vest B Effective in cooling down

temperature

Limited (temporary and

partly) cooling capacity

Light Thermal discomfort

Good effect of the fans Problems of fan, fabric and

batteries

Inconvenient to wash

4.4. Determination of the cooling capacity of the selected cooling vest

4.4.1 Protocol of treadmill running test inside a climatic chamber

Core temperature and heart rate were collected continuously and

simultaneously during the test. Core temperature was measured by an

ingestible CorTemp™ (HQInc., America) thermometer sensor (capsule) with a

CorTemp™ data recorder at a sampling frequency of 30 seconds. The data

recorder can detect the signal from the CorTemp™ sensor, then displays and

stores the data in memory. The data are transferred to a PC platform via the

CorTrack™ II software. Heart rate was measured outside the chamber by

Polar® (Finland) belt A every 60-second, and was measured inside the

chamber by Polar® belt B every second. The latter will transfer the data to the

computer through a sensor in the treadmill (h/p/cosmos® , Germany) which

synchronously records with running speed, distance, and time after installing

h/p/cosmos para control® and h/p/cosmos para graphics® . Appendix B

provides the figures of the abovementioned equipment.

The protocol of treadmill running test inside a climatic chamber is illustrated in

Table 4.4.1. Twenty-two healthy and fit participants were recruited from The

Hong Kong Polytechnic University and the Technological and Higher

Education Institute of Hong Kong. Participants having cardiovascular, or

oesophageal and other diseases would not be allowed to participate in this test.



Selected participants were briefed the details of the climatic chamber treadmill

test, its objectives, requirements for participation, and potential risks prior to

the experiment. A day before the test, calibration of each capsule was

conducted to ensure its functionality. Then the calibrated capsule would be

delivered to the participant who would ingest it with warm water before s/he

went to bed. On the day of the test, the climatic chamber would be set and kept

constant at 33 °C and 75% respectively. As soon as the participant arrived,

s/he would be fed with breakfast or snack. After a proper briefing on the

protocol of treadmill running test, the participant was asked to complete some

basic demographic information and a consent form approved by the Human

Subjects Ethics Sub-committee of The Hong Kong Polytechnic University. A

registered nurse was engaged to station inside the chamber throughout the

whole exercise and would provide necessary medical care in case of

emergency.

The participants were asked to rest outside chamber for 30 minutes. Then they

were asked to wear a unified sportswear (a T-shirt and shorts) and Polar® belt

B, and rested on a backless chair inside the chamber for another 30 minutes to

get acclimated to the climatic chamber conditions. To minimize systematic

errors, the participants were randomly assigned to wear or not to wear a

cooling vest in the first running and recovery. This would be reversed in the

second running and recovery. The participants were initially asked to run at 5

km/h with 1% slope. The speed and slope would increase progressively to 9.5

km/h and 7%. The participants would be allowed to stop when their core

temperature reached 38.5 °C or if they were exhausted and requested to stop.

The participants would then be asked to rest and recover inside the chamber

for 40 minutes; and outside the chamber at room temperature for 20 minutes

or sooner to cool their core temperature down to the value before the first run.

In the second run, the participants would be asked to run with the same

progressive intensity and stopped when their core temperature reached

38.5 °C. After the second running, the participants would rest for 40 minutes

inside the climatic chamber. The participants’ core temperature, heart rate

would be monitored continuously and simultaneously throughout the entire

running and resting periods. Following each running and recovery period,

participants would be asked to report their RPE.

Table 4.4.1 Protocol of treadmill running test inside a climatic chamber

Duration Task

The day before test Calibration of capsule

Participants ingest capsule

30 min Chamber preparation;

Provide breakfast/snack;

Consent and basic demographic information



30 min Rest outside the chamber

30 min Rest inside the chamber for adaptation

~ 30 min Start the 1st running with/without cooling vest;

- Increase the intensity of running progressively (Table 4.4.1a)

- Stop running when Tc of the participant reaches 38.5°C

40 min 1st recovery with/without cooling vest inside the climatic chamber

~20 min Rest outside the chamber

~ 30 min Start the 2nd running without/with cooling vest;

- Increase the intensity of running progressively (Table 4.4.1a)

- Stop running when Tc of the participant reaches 38.5°C

40 min 2nd recovery without/with cooling vest inside the climatic chamber

End

Table 4.4.1a Intensity of treadmill running test

Stage Duration Cumulated

Duration

Speed

(km/h)

Slope (%)

1. Constant 3min 3min 5 1

3min 6min 5 1

3min 9min 5 1

2. Increasing

speed

3min 12min 6.5 1

3min 15min 8 1

3min 18min 9.5 1

3. Increasing

slope

3min 21min 9.5 3

3min 24min 9.5 5

3min 27min 9.5 7

Thereafter… 3min 9.5 +2

Last stage* 5 min 3.5 0

5 min 2 0

*: A cool-down procedure will be provided after the participant stops running.

4.4.2 Records of treadmill running test

Records of twelve treadmill running tests are shown in Table 4.4.2. Among the

twelve participants, 10 were male and 2 were female. The mean age was 22,

ranged from 18 to 30. The mean weight and height was 63.77 kg and 169.78

cm, respectively. In addition, another 10 treadmill running tests were

conducted but not included in the analysis because the participants were

exhausted and stopped before their core temperature reached 38.5 °C; and/or

the core temperature could not be detected by the sensor.



Table 4.4.2 Record of treadmill running test

Date Condition Gender Age Weight (kg) Height (cm)

29-Nov-12 W/O COOL first M 20 58.53 172

7-Jan-13 W COOL first M 18 74.71 181.8

9-Jan-13 W/O COOL first M 19 63.44 171

10-Jan-13 W COOL first M 20 71.63 167

23-Jan-13 W/O COOL first M 23 54.46 164.5

2-Feb-13 W COOL first M 30 64.01 174

19-Feb-13 W/O COOL first M 26 57.34 168

23-Feb-13 W COOL first M 25 74.73 168

1-Mar-13 W/O COOL first M 30 62.75 165

2-Mar-13 W COOL first F 21 65.94 173

8-Mar-13 W/O COOL first F 19 63.33 170

3-Apr-13 W COOL first M 18 54.38 163

Mean ± SD 22±4.38 63.77 ± 7.08 169.78 ± 5.13

4.4.3 Results of treadmill running test

In order to estimate the level of strain and to initiate appropriate actions at an

early stage, Moran et al. (1998) introduced the Physiological Strain Index (PSI),

which is based on heart rate and core temperature records in humans, to

describe heat strain in quantitative terms during continuous exercise (Gotshall

et al., 2004). PSI is therefore applied in this study to measure how the selected

personal cooling equipment alleviates the heat strain process. PSI has been

shown to effectively differentiate the heat strain associated with different

climatic conditions, hydration levels, types of clothing including protective

clothing, different exercise intensities, gender, and the effects of aging (Moran

et al., 2002; Moran et al., 1999a; Moran et al., 1999b). It is an algorithm

combining data from the heart rate and core temperature, in which output is

scaled from 0 to 10 where 0 represents no strain and 10 very high

physiological strain. The mathematical expression of PSI can be found in

equation (2.1).

PSI = 5 * (Tci - Tc0)/ (39.5 - Tc0) + 5 * (HRi - HRo) / (180-HR0) (2.1)

Where Tco and HRo are the minimum values recorded during the 30-minute

rest outside the chamber; Tci and HRi are simultaneous measurements taken

at any time whilst the participant is under the controlled heat exposure. HRi is

the average value on every 30-second. And 39.5 °C and 180 bpm represent

maximal core temperature and heart rate respectively.



Descriptive statistics are summarized in Table 4.4.3. During exercise, mean

value of core temperature with cooling vest was 38.05 °C, which was

marginally higher than that without (38.00 °C). Mean value of heart rate with

cooling vest was 158.12 bpm, which was somewhat lower than that without

(158.20 bpm). Similarly, mean value of PSI with cooling vest was also lower

than that without (6.12 vs. 6.17). The participants running with cooling vest felt

somewhat hard with RPE of 4.5, while they felt hard without cooling vest with

RPE about 5. During recovery, mean value of core temperature with cooling

vest was lower than that without (38.42 °C vs. 38.46 °C). Mean value of heart

rate with cooling vest was much lower than that without (118.74 bpm vs.

121.82 bpm). Mean value of PSI with cooling vest was also lower than that

without (4.83 vs. 5.12). Similarly, the participants felt more comfortable (RPE)

with cooling vest than without during recovery (2.30 vs. 3.00).

Table 4.4.3 Descriptive statistics

Activity Parameter

With cooling vest Without cooling vest Difference

between

mean

values

Mean ± SD Range Mean ± SD Range

Exercise

Ave Tc

(°C)

38.05±0.38 37.12~38.59 38.00±0.37 37.06~38.55 -0.05

Ave HR

(bpm)

158.12±25.30 79.4~209.14 158.20±28.05 76.93~202.11 0.08

Ave PSI 6.12±1.38 1.52~9.33 6.17±1.30 1.75~8.82 0.05

RPE 4.45±1.37 3~7 5.09±2.12 2~9 0.64

Recovery

Ave Tc

(°C)

38.42±0.57 37.43~39.39 38.46±0.55 37.48~39.34 0.04

Ave HR

(bpm)

118.74±17.55 75~198.81 121.82±15.97 82.93~201 3.08

Ave PSI 4.83±2.02 1.18~9.15 5.12±1.66 1.76~9 0.29

RPE 2.30±0.95 1~4 3.00±1.15 1~5 0.70

Exercise

Core temperature, Tc

The trends of average Tc, HR and PSI changed over 30 seconds during

exercise and recovery were plotted. Linear regression analysis between the

physiological response and duration was conducted to compute the gradient of

each curve. Figure 4.4.1 depicts the scattered plots and linear curves of

average Tc with and without cooling vest respectively. Rate of increase

(gradient) of average Tc without cooling vest was faster than that with, which



was reinforced by the regression equations (3.1) and (3.2). Gradient of

average Tc with cooling vest was gentler than that without (0.025 °C /min vs.

0.026 °C /min). Taking 40.5 °C as a threshold where heat stroke might occur

(Vicario et al., 1986; Menaker et al., 2011), participants without a cooling vest

would take 111 min to reach this threshold, and participants wearing a cooling

vest would take 113 min. A 1.35 % improvement was observed with the use of

a cooling vest in terms of cooling down the core temperature.

Figure 4.4.1 Scattered plots and linear curves of average Tc - with vs. without cooling

vest during exercise

Tcw/o= 37.594 + 0.026 D + ε (Adj R2=0.961, p<0.001) (3.1)

Tcw=37.668 + 0.025 D + ε (Adj R2=0.963, p<0.001) (3.2)

where Tcw/o refers to average Tc (°C) without cooling vest, Tcw refers to

average Tc (°C) with cooling vest, D is duration (min), ε is the error term.

Heart rate, HR

Scattered plots and linear curves of average HR with and without cooling vest

are illustrated in Figure 4.4.2. It is observed that rate of increase (gradient) of

average HR without cooling vest was faster than that with. Equations (3.3)-(3.4)

also show that the gradient of heart rate without cooling vest is steeper than

that with (2.395 bpm/min vs.2.184 bpm/min). Taking a threshold of 200 bpm,

participants without a cooling vest would take 33 min to reach this threshold,

and participants wearing a cooling vest would take 35 min. A 5.74 %

improvement was observed with the use of a cooling vest in terms of reaching



a dangerous level of heart rate during exercise.

Figure 4.4.2 Scattered plots and linear curves of average HR - with vs. without cooling


HRw/o= 120.488 + 2.395 D + ε (Adj R2=0.883, p<0.001) (3.3)

HRw=123.329+ 2.184 D + ε (Adj R2=0.857, p<0.001) (3.4)

where HRw/o refers to average heart rate (bpm) without cooling vest, HRw

refers to average heart rate (bpm) with cooling vest, D is duration (min), ε is the

error term.

Physiological strain index, PSI

Scattered plots and linear curves of average PSI with and without cooling vest

are illustrated in Figure 4.4.3. It is obvious that rate of increase (gradient) of

average PSI without cooling vest was faster than that with. Equations

(3.5)-(3.6) also show that the gradient of PSI without cooling vest is steeper

than that with (0.183/min vs. 0.161/min). Taking a maximal score of 10 for PSI,

participants without a cooling vest would take 37 min to reach this threshold,

and participants wearing a cooling vest would take 40 min. A 6.69 %

improvement was observed with the use of a cooling vest in terms of reaching

the maximal score of 10 for PSI.



Figure 4.4.3 Scattered plots and linear curves of average PSI - with vs. without cooling


PSIw/o= 3.125 + 0.183 D + ε (Adj R2=0.977, p<0.001) (3.5)

PSIw=3.547+ 0.161 D + ε (Adj R2=0.907, p<0.001) (3.6)

where PSIw/o refers to average physiological strain index without cooling vest,

PSIw refers to average physiological strain index with cooling vest, D is

duration (min), ε is the error term.

Recovery

Core temperature, Tc

Figure 4.4.4 depicts the scattered plots and linear curves of average Tc with

and without cooling vest during recovery respectively. Rate of reduction

(gradient) of average Tc with cooling vest was faster than that without. It can

be also observed by the regression equations (3.7) and (3.8). Gradient of

average Tc with cooling vest was steeper than that without (0.028 °C /min vs.

0.026 °C /min). Taking a baseline of 37 °C, participants without a cooling vest

would take 79 min to reduce to this level, and participants wearing a cooling

vest would take 74 min. A 5.19 % improvement was observed with the use of a

cooling vest in terms of reducing the core temperature down to a comfortable

level.



Figure 4.4.4 Scattered plots and linear curves of average Tc - with vs. without cooling

vest during recovery

Tcw/o= 39.042 – 0.026 D + ε (Adj R2=0.986, p<0.001) (3.7)

Tcw=39.085– 0.028 D + ε (Adj R2=0.982, p<0.001) (3.8)

where Tcw/o refers to average Tc (°C) without cooling vest, Tcw refers to

average Tc (°C) with cooling vest, D is duration (min), ε is the error term.

Heart rate, HR

Scattered plots and linear curves of average HR with and without cooling vest

during recovery are illustrated in Figure 4.4.5. The rate of reduction (gradient)

of average HR with cooling vest was remarkably faster than that without, and

the absolute values of average HR with cooling vest were lower than those

without. The regression equations (3.9) and (3.10) also reinforce that gradient

of average HR with cooling vest was steeper than that without (1.288 bpm/min

vs. 1.224 bpm/min). Taking a baseline of 70 bpm, participants without a cooling

vest would take 62 min to reduce to this level, and participants wearing a

cooling vest would take 58 min. A remarkable 6.83 % improvement was

observed with the use of a cooling vest in terms of bringing the heart rate down

to a comfortable level.



Figure 4.4.5 Scattered plots and linear curves of average HR - with vs. without cooling


HRw/o= 146.390 – 1.224 D + ε (Adj R2=0.788, p<0.001) (3.9)

HRw=144.891– 1.288 D + ε (Adj R2=0.771, p<0.001) (3.10)

where HRw/o refers to average heart rate (bpm) without cooling vest, HRw

refers to average heart rate (bpm) with cooling vest, D is duration (min), ε is the

error term.

Physiological strain index, PSI

Figure 4.4.6 depicts the scattered plot and linear curves of average PSI with

and without cooling vest during recovery respectively. Rate of reduction

(gradient) of average PSI with cooling vest was faster than that without, and

the absolute values of average PSI with cooling vest were lower than those

without, which can be also observed by the regression equations (3.11) and

(3.12). Gradient of average PSI with cooling vest was steeper than that without

(0.102/min vs. 0.098/min). Taking a baseline of 1[19] for PSI, participants without

a cooling vest would take 62 min to reduce to this level, and participants

wearing a cooling vest would take 58 min. A remarkable 6.82 % improvement

was observed with the use of a cooling vest in terms of reducing the PSI down

to a comfortable level.

[19] “1” was used as a baseline instead of “0” because there is a diminishing marginal returns on recovery, the participant may not be able to return to “0” PSI in a short instance (Chan et al, 2012).



Figure 4.4.6 Scattered plots and linear curves of average PSI - with vs. without cooling


PSIw/o= 7.123 – 0.098 D + ε (Adj R2=0.941, p<0.001) (3.11)

PSIw=6.938 – 0.102 D + ε (Adj R2=0.895, p<0.001) (3.12)

where PSIw/o refers to average physiological strain index without cooling vest,

PSIw refers to average physiological strain index with cooling vest, D is

duration (min), ε is the error term.

5. Recommendations

Results of twelve field studies indicated that most workers in four industries

preferred Vest B because it had better thermal comfort, usability, fabric hand

(feel), and tactile comfort than Vest A. These four underlying factors could

affect workers’ preference for a cooling vest. Rating of perceived exertion after

work with Vest A was somewhat harder than that with Vest B; although the

physiological responses of Vest A and Vest B had no significant differences.

Similarly, no significant differences of perceived cooling effective time were

observed between these two cooling vests.

Vest B was therefore recommended for further testing inside a climatic

chamber which was approved by OSHC. Twelve treadmill running tests were

conducted to quantitatively evaluate the cooling capacity of the selected

cooling vest inside a climatic chamber. The environmental condition of the

climatic chamber was set and kept constant at 33 °C and 75 % relative

humidity. During exercise, it was observed that rates of increase of average



Tc/HR/PSI with cooling vest were slower than those without. Projecting these

physiological responses to maximal levels, the time required to reach the

maximal levels are longer when wearing cooling vest. Cooling vest also

enhances thermoregulatory recovery. During recovery, it was observed that

rates of reduction of average Tc/HR/PSI with cooling vest were faster than

those without. This implies that reductions in these physiological responses to

comfortable levels are faster when wearing cooling vest. Additionally, the time

required for Tc, HR and PSI to return to comfortable levels are shorter with the

cooling vest. The cooling vest under scrutiny was found to be able to slow

down the rates of increase of Tc/HR/PSI during working period (6.69%),

but accelerate their rates of reduction during recovery (6.82%); hence its

effectiveness was demonstrated.

However, the selected cooling vest (Vest B) is not without limitations. The dark

colour will absorb heat from the sun, thus attracting more radiant heat load

onto outdoor workers. Some workers commented that the ice pads inserted

into Vest B have little cooling effect because of small size and limited coverage

on the body surface area. Moreover, the fan could draw hot air from the

surrounding environment. Vest B also requires constant replacement of gel

pads and batteries. A cooling vest with a lower total mass and greater cooling

capacity will be more acceptable (Webster et al., 2005). Some suggestions

have been made to the design of the cooling vest. For example, horticultural

and cleaning workers proposed that the fabric should be more durable and

anti-scratch, while kitchen and catering workers proposed that it should be

stain-resistant and fire-resistant to suit their job nature. Construction workers

and airport apron workers proposed that reflective strip should be a built-in

feature of the cooling vest to save them from wearing an extra reflective vest.

Furthermore, freezing of gel pads needs additional refrigerators and extra

space for preparation and storage. Maintenance and cleaning of cooling vests

also need further consideration. Therefore, a comprehensive implementation

plan should be in place before introducing the personal cooling equipment to

various industries at large.



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7. Appendices

Appendix A

Figure 1a: Heat Stress

Monitor

QUESTemp° 36™

Figure 1b: Ear Temperature

Monitor

OMRON® , MC-509N

Figure 1c: Blood Pressure

Monitor

Boso-medistar S™

Table 1. Rating of Perceived Exertion Scale



Table 2. A Blank Questionnaire (Brown: Vest A; Black: Vest B)



Appendix B

Figure 2a. CorTemp®

thermometer sensor and

CorTemp® data recorder

Figure 2b. Polar Wearlink®

Belt A

Figure 2c. Polar® T34

Transmitter

Belt B

Figure 2g. CorTrack™ II

software

Figure 2h. Climatic chamber

Figure 2d. h/p/cosmos®

treadmill

Figure 2e. h/p/cosmos

para control®

Figure 2f. h/p/cosmos

para graphic®

study on the effectiveness of personal cooling equipment

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