tlvs for heat stress

Mike Slater

Threshold Limit Values ® (TLVs) for heat stress are included in the American Conference of Governmental Industrial Hygienists (ACGIH) TLV booklet

TLVs® are guidelines designed for use by occupational hygienists in making decisions regarding safe levels of exposure to various chemical substances and physical agents found in the workplace.

This flowchart summarises how to apply the TLV’s. However. It’s quite complex. We’ll go through

it step by step

Screening Detailed Analysis

Heat Strain Monitoring

General approach

Screening Detailed Analysis

Heat Strain Monitoring

General approach

STOP Heat Stress expected?

NO

YES

SCREENING

Clothing adjustment factors

available?

YES

NO

Screening

TLV Clothing Corrections

Clothing Type WBGT Correction

Work clothes (long sleeve and pants) 0

Cloth (woven material) coveralls 0

Double layer woven clothing 3

SMS polypropylene coveralls 0.5

Polyolefin overalls 1

Limited use vapour-barrier overalls 11

Clothing adjustment factors

available?

YES

NO

Screening

If no clothing adjustment factors are available, go straight to heat strain (physiological) monitoring

Clothing adjustment factors

available?

YES

NO

Screening

This may be necessary, for example, where chemical protective suits are being worn

TLV Clothing Corrections

Clothing Type WBGT Correction

Work clothes (long sleeve and pants) 0

Cloth (woven material) coveralls 0

Double layer woven clothing 3

SMS polypropylene coveralls 0.5

Polyolefin overalls 1

Limited use vapour-barrier overalls 11

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

YES

YES

NO

NO

Screening

Work out the WBGT from the results of environmental measurements and apply the clothing corrections

WBGT Index

No direct exposure to sunlight WBGT = 0.7 tnwb + 0.3 tg

With direct exposure to sunlight WBGT = 0.7 tnwb + 0.2 tg + 0.1 ta

Compare the corrected WBGT with the Action Limit Values

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

To use this table you have to know • the time spent working and resting • the metabolic rate

Metabolic rate categories

Category Metabolic Rate (W)

Examples

Rest 115 Sitting

Light 180 Sitting or standing Light hand / arm work

Moderate 300 Walking Moderate lifting

Heavy 415 Heavy materials handling

Very Heavy 520 Pick and shovel work

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

So, for a job involving moderate work where 75% of the time is spent working and 25% resting

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

If the adjusted WBGT is below this value the Action Limit is not exceeded

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

YES

YES

Low Risk

NO

NO

Screening

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

YES

YES

Low Risk Continue work

Monitor

NO

NO

Screening

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

Are screening criteria for TLV

exceeded?

YES

YES

YES

Low Risk Continue work

Monitor

NO

NO

NO

Screening

If the Action Limit is exceeded then the WBGT value is compared with the TLV criteria

ACGIH TLVs – Screening TLV

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 31.0 28.0 - -

50% to 75% 31.0 29.0 27.5 -

25% to 50% 32.0 30.0 29.0 28.0

0 to 25% 32.5 31.5 30.5 30.0

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

Are screening criteria for TLV

exceeded?

YES

YES

YES

Low Risk Continue work

Monitor

Implement general controls

NO

NO

NO

Screening

General controls

Information, instruction & training

Regular drinks of water

Self regulation

Health screening and surveillance Encourage reporting symptoms

Encourage healthy lifestyles

Monitoring

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

Are screening criteria for TLV

exceeded?

YES

YES

YES

Low Risk Continue work

Monitor

Implement general controls

Continue work Maintain controls

Monitor

NO

NO

NO

Screening

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

Are screening criteria for TLV

exceeded?

YES

YES

YES

Low Risk Continue work

Monitor

Implement general controls

Continue work Maintain controls

Monitor

NO

NO

NO

Screening

Are data available for detailed

analysis?

YES

NO

Detailed analysis

If the TLV is exceeded, consider carrying out a more detailed analysis using a more sophisticated method, such as the Predicted Heat Strain (PHS) index

Are data available for detailed

analysis?

Action Limit exceeded?

YES

YES

NO

NO

Detailed analysis

The Action Limit referred to here is that associated with the index being used NOT the ACGIH Action Limit

Are data available for detailed

analysis?

Action Limit exceeded?

YES

YES

NO

NO

Detailed analysis

Are data available for detailed

analysis?

Action Limit exceeded?

YES

YES

Low Risk

NO

NO

Detailed analysis

Are data available for detailed

analysis?

Action Limit exceeded?

YES

YES

Low Risk Continue work

Monitor

NO

NO

Detailed analysis

Are data available for detailed

analysis?

Action Limit exceeded?

TLV exceeded?

YES

YES

YES

Low Risk Continue work

Monitor

NO

NO

NO

Detailed analysis

The TLV referred to here is the limit value associated with the index being used NOT the ACGIH Screening TLVs

Are data available for detailed

analysis?

Action Limit exceeded?

TLV exceeded?

YES

YES

YES

Low Risk Continue work

Monitor

NO

NO

NO

Detailed analysis

Are data available for detailed

analysis?

Action Limit exceeded?

TLV exceeded?

YES

YES

YES

Low Risk Continue work

Monitor

Implement general controls

NO

NO

NO

Detailed analysis

Are data available for detailed

analysis?

Action Limit exceeded?

TLV exceeded?

YES

YES

YES

Low Risk Continue work

Monitor

Implement general controls

Continue work Maintain controls

Monitor

NO

NO

NO

Detailed analysis

TLV exceeded?

YES

Implement general controls

Continue work Maintain controls

Monitor

NO

Heat strain monitoring

What if the TLV is exceeded?

TLV exceeded?

YES

Implement general controls

Continue work Maintain controls

Monitor

NO

Heat strain monitoring

Perform heat strain (physiological)

monitoring

Physiological assessment

Core Temperature Heart rate

Personal Monitor

Miner’s Core Temperature & Heart Rate

Source: OHTA.

TLV exceeded?

Excessive heat strain based on

monitoring?

YES

YES

Implement general controls

Continue work Maintain controls

Monitor

NO

NO

Heat strain monitoring

Perform heat strain (physiological)

monitoring

Guidelines for limiting Heat Strain

Factor Work should be discontinued if:

Heart rate (beats per minute) Greater than 180 minus age in years

Core temperature Greater than 38.5 0C (acclimatised) Greater than 38.0 0C (unacclimatised)

Recovery heart rate (beats per minute)

120 (at one minute after peak work)

Other Symptoms of sudden and severe fatigue, nausea, dizziness or lightheadedness

TLV exceeded?

Excessive heat strain based on

monitoring?

YES

YES

Implement general controls

Continue work Maintain controls

Monitor

NO

NO

Heat strain monitoring

Perform heat strain (physiological)

monitoring

TLV exceeded?

Excessive heat strain based on

monitoring?

YES

YES

Implement general controls

Continue work Maintain controls

Monitor

NO

NO

Heat strain monitoring

Perform heat strain (physiological)

monitoring

Implement Job-specific controls

Job-specific controls

Engineering controls

Administrative controls

Personal protective equipment

TLV exceeded?

Excessive heat strain based on

monitoring?

YES

YES

Implement general controls

Continue work Maintain controls

Monitor

NO

NO

Heat strain monitoring

Perform heat strain (physiological)

monitoring

Implement Job-specific controls

TLV exceeded?

Excessive heat strain based on

monitoring?

YES

YES

Implement general controls

Continue work Maintain controls

Monitor

NO

NO

Heat strain monitoring

Perform heat strain (physiological)

monitoring

Implement Job-specific controls

At workstation Ta = 24 0C

Tw = 22 0C

Tg = 28 0C

V = 0.4 m/s

Work involves monitoring process Minimal manual effort required Standard overalls worn

WBGT Index

No direct exposure to sunlight WBGT = 0.7 tnwb + 0.3 tg

With direct exposure to sunlight WBGT = 0.7 tnwb + 0.2 tg + 0.1 ta

At workstation Ta = 24 0C

Tw = 22 0C

Tg = 28 0C

V = 0.4 m/s

WBGT = 23.8 0C

Clothing adjustment factors

available?

YES

NO

Screening

TLV Clothing Corrections

Clothing Type WBGT Correction

Work clothes (long sleeve and pants) 0

Cloth (woven material) coveralls 0

Double layer woven clothing 3

SMS polypropylene coveralls 0.5

Polyolefin overalls 1

Limited use vapour-barrier overalls 11

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

YES

YES

NO

NO

Screening

Metabolic rate categories

Category Metabolic Rate (W)

Rest 115

Light 180

Moderate 300

Heavy 415

Very Heavy 520

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

WBGT = 23.8 0C

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

YES

YES

Low Risk

NO

NO

Screening

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

YES

YES

Low Risk Continue work

Monitor

NO

NO

Screening

Boiler Cleaning

Air

temp.

(0C)

Wet

bulb

temp.

(0C)

Globe

temp.

(0C)

Air

velocity

(m/s)

Start of work 34 19 51 0.2

After 5 hours 32.5 18.5 51.5 0.2

Heavy manual effort required Standard overalls worn

Air

temp.

(0C)

Wet

bulb

temp.

(0C)

Globe

temp.

(0C)

Air

velocity

(m/s)

Start of work 34 19 51 0.2

After 5 hours 32.5 18.5 51.5 0.2

WBGT = 28.6 0C

Boiler Cleaning

Clothing adjustment factors

available?

YES

NO

Screening

TLV Clothing Corrections

Clothing Type WBGT Correction

Work clothes (long sleeve and pants) 0

Cloth (woven material) coveralls 0

Double layer woven clothing 3

SMS polypropylene coveralls 0.5

Polyolefin overalls 1

Limited use vapour-barrier overalls 11

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

YES

YES

NO

NO

Screening

Metabolic rate categories

Category Metabolic Rate (W)

Rest 115

Light 180

Moderate 300

Heavy 415

Very Heavy 520

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

WBGT = 28.6 0C So Action Limit is exceeded

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

Are screening criteria for TLV

exceeded?

YES

YES

YES

NO

NO

Screening

ACGIH TLVs – Screening TLV

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 31.0 28.0 - -

50% to 75% 31.0 29.0 27.5 -

25% to 50% 32.0 30.0 29.0 28.0

0 to 25% 32.5 31.5 30.5 30.0

ACGIH TLVs – Screening TLV

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 31.0 28.0 - -

50% to 75% 31.0 29.0 27.5 -

25% to 50% 32.0 30.0 29.0 28.0

0 to 25% 32.5 31.5 30.5 30.0

WBGT = 28.6 0C So TLV is NOT exceeded provided work is restricted to 50% of shift

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

Are screening criteria for TLV

exceeded?

YES

YES

YES

Low Risk Continue work

Monitor

Implement general controls

NO

NO

NO

Screening

Reduce risk

Allow boiler to cool down before starting work

Working methods

Mechanical aids

Self pacing

Manage exposure time

Implement work:rest regime

Work restricted to 25% to 50% of work cycle

Provide information, instruction and training

Risks

Good working practice

Symptoms to look out for

Provide water

Drink at regular intervals

Health surveillance

Pre-placement medical screening

Regular health checks

Encourage reporting of symptoms

Encourage healthy lifestyle

Diet

Exercise

Moderate alcohol consumption

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

Are screening criteria for TLV

exceeded?

YES

YES

YES

Low Risk Continue work

Monitor

Implement general controls

Continue work Maintain controls

Monitor

NO

NO

NO

Screening

Furnace Repair

Air

temp.

(0C)

Wet bulb

temp.

(0C)

Globe

temp.

(0C)

Air

velocity

(m/s)

98 45 150 1

Heavy manual effort required Thick, woollen clothing worn

Furnace Repair

Air

temp.

(0C)

Wet bulb

temp.

(0C)

Globe

temp.

(0C)

Air

velocity

(m/s)

98 45 150 1

WBGT = 76.5 0C

TLV Clothing Corrections

Clothing Type WBGT Correction

Work clothes (long sleeve and pants) 0

Cloth (woven material) coveralls 0

Double layer woven clothing 3

SMS polypropylene coveralls 0.5

Polyolefin overalls 1

Limited use vapour-barrier overalls 11

TLV Clothing Corrections

Clothing Type WBGT Correction

Work clothes (long sleeve and pants) 0

Cloth (woven material) coveralls 0

Double layer woven clothing 3

SMS polypropylene coveralls 0.5

Polyolefin overalls 1

Limited use vapour-barrier overalls 11

Furnace Repair

Air

temp.

(0C)

Wet bulb

temp.

(0C)

Globe

temp.

(0C)

Air

velocity

(m/s)

98 45 150 1

Corrected WBGT = 79.5 0C

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

YES

YES

NO

NO

Screening

Metabolic rate categories

Category Metabolic Rate (W)

Rest 115

Light 180

Moderate 300

Heavy 415

Very Heavy 520

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

ACGIH TLVs – Action Limit

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 28.0 25.0 - -

50% to 75% 28.5 26.0 24.0 -

25% to 50% 29.5 27.0 25.5 24.5

0 to 25% 30.0 29.0 28.0 27.0

Corrected WBGT = 79.5 0C So Action Limit is exceeded

Clothing adjustment factors

available?

Are screening criteria for Action Limit exceeded?

Are screening criteria for TLV

exceeded?

YES

YES

YES

NO

NO

Screening

ACGIH TLVs – Screening TLV

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 31.0 28.0 - -

50% to 75% 31.0 29.0 27.5 -

25% to 50% 32.0 30.0 29.0 28.0

0 to 25% 32.5 31.5 30.5 30.0

ACGIH TLVs – Screening TLV

Allocation of work in work cycle

Workload

Light Moderate Heavy V ery heavy

75% to 100% 31.0 28.0 - -

50% to 75% 31.0 29.0 27.5 -

25% to 50% 32.0 30.0 29.0 28.0

0 to 25% 32.5 31.5 30.5 30.0

Corrected WBGT = 79.5 0C Corrected WBGT = 79.5 0C So TLV is exceeded

Are data available for detailed

analysis?

YES

NO

Are screening criteria for TLV

exceeded?

YES

Detailed analysis Perform heat strain

(physiological) monitoring

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mike@diamondenv.co.uk

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Twitter: @diamondenv

Mike Slater

Mike Slater, Diamond Environmental Ltd. (mike@diamondenv.co.uk)

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