noise levels in critical control spaces aboard a modernized ...ryan, lt(n) fernandez, lt(n) monette...

Defence Research and Development Canada Scientific Report DRDC-RDDC-2018-R156 June 2018

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Noise levels in critical control spaces aboard a modernized Halifax-class patrol frigate Implications for communication effectiveness

Ann Nakashima Wenbi Wang Jane Cai DRDC – Toronto Research Centre

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Template in use: (2017) SR Advanced Template_EN_4_2018-05-03_v1_WW.dotm © Her Majesty the Queen in Right of Canada (Department of National Defence), 2018 © Sa Majesté la Reine en droit du Canada (Ministère de la Défense nationale), 2018

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IMPORTANT INFORMATIVE STATEMENTS

This document was reviewed for Controlled Goods by Defence Research and Development Canada (DRDC) using the Schedule to the Defence Production Act.

Disclaimer: Her Majesty the Queen in right of Canada, as represented by the Minister of National Defence ("Canada"), makes no representations or warranties, express or implied, of any kind whatsoever, and assumes no liability for the accuracy, reliability, completeness, currency or usefulness of any information, product, process or material included in this document. Nothing in this document should be interpreted as an endorsement for the specific use of any tool, technique or process examined in it. Any reliance on, or use of, any information, product, process or material included in this document is at the sole risk of the person so using it or relying on it. Canada does not assume any liability in respect of any damages or losses arising out of or in connection with the use of, or reliance on, any information, product, process or material included in this document.

Endorsement statement: This publication has been peer-reviewed and published by the Editorial Office of Defence Research and Development Canada, an agency of the Department of National Defence of Canada. Inquiries can be sent to: [email protected].

DRDC-RDDC-2018-R156 i

Abstract

As part of ongoing efforts to investigate human factors issues that affect human performance on current naval platforms, a noise survey and communication study was conducted on the HMCS Montreal. The results will provide guidance on the optimization of layout within critical control space on future naval platforms. The average noise levels in four critical control spaces, the Bridge, operations room, communications control room (CCR) and machinery control room (MCR), exceeded the North Atlantic Treaty Organisation (NATO) Standardisation Agreement (STANAG) 4293 limits. The noise levels were the highest in the CCR, indicating that increased vocal effort is required to communicate over short distances. The questionnaire results indicated that CCR crewmembers had more difficulty with face-to-face communication than crewmembers in other control rooms. Noise levels logged from the communication headsets in the Bridge and operations room were high enough to cause concern for headset noise exposure when the headset was at full volume. The results provide information about noise levels during quiet watch and action stations in four critical control spaces, which will support modeling and simulation efforts for workplace layout optimization.

Significance to defence and security

This is the only known study of noise and communication on a modernized Canadian Patrol Frigate that has included control spaces other than the Bridge and operations room. The human factors issues that were identified in four critical control spaces will help to inform the layout design of future naval platforms.

ii DRDC-RDDC-2018-R156

Résumé

Dans le cadre des efforts continus visant à étudier les facteurs humains qui influent sur la performance humaine sur les plateformes navales actuelles, une étude sur le bruit et les communications a été menée à bord du NCSM Montréal. Les résultats orienteront l’aménagement optimisé des espaces de contrôle critiques des futures plateformes navales. Les niveaux de bruit moyens dans quatre espaces de contrôle critiques (c.-à-d. la passerelle, la salle des opérations, la salle de contrôle des communications [SCC] et la salle de contrôle des machines [MCR]) dépassaient les limites de l’accord de normalisation (STANAG 4293) de l’Organisation du Traité de l’Atlantique Nord (OTAN). Les niveaux de bruit les plus élevés étaient dans la SCC, ce qui indique qu’il faut parler plus fort pour communiquer sur de courtes distances. Les résultats du questionnaire démontrent que les membres d’équipage de la SCC ont plus de difficulté à communiquer en personne que les membres d’équipage des autres salles de contrôle. Les niveaux de bruit enregistrés à partir des casques d’écoute de la passerelle et de la salle des opérations étaient suffisamment élevés pour entraîner des problèmes d’exposition au bruit lorsque le casque d’écoute est à plein volume. Les résultats fournissent également de l’information sur les niveaux de bruit dans quatre espaces de contrôle critiques pendant les heures creuses des postes de surveillance et de combat, ce qui appuiera les efforts de modélisation et de simulation pour l’optimisation de l’aménagement du lieu de travail.

Importance pour la défense et la sécurité

Il s’agit de la seule étude connue sur le bruit et les communications d’une frégate de patrouille canadienne modernisée qui comprend des espaces de contrôle autres que la passerelle et la salle des opérations. Les problèmes liés aux facteurs humains qui ont été cernés dans quatre espaces de contrôle critiques permettront d’orienter l’aménagement des futures plateformes navales.

DRDC-RDDC-2018-R156 iii

Table of contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i Significance to defence and security . . . . . . . . . . . . . . . . . . . . . . . . . i Résumé . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii Importance pour la défense et la sécurité . . . . . . . . . . . . . . . . . . . . . . . ii Table of contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii List of figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv List of tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.3 Noise exposure and speech interference . . . . . . . . . . . . . . . . . . . . 1 1.4 Previous work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Materials and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1 Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3 Data analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1 Overall noise levels, speech interference and noise rating . . . . . . . . . . . . . 8 3.2 Headset noise levels . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.3 Noise levels in other areas . . . . . . . . . . . . . . . . . . . . . . . . 12

4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.1 Background noise levels and speech interference . . . . . . . . . . . . . . . 13 4.2 Communication headset noise . . . . . . . . . . . . . . . . . . . . . . 14 4.3 Hearing conservation . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.4 Voice communication questionnaire . . . . . . . . . . . . . . . . . . . . 15

5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Annex A Voice communication questionnaire . . . . . . . . . . . . . . . . . . . . 20 Annex B Supplementary data . . . . . . . . . . . . . . . . . . . . . . . . . . 28 List of symbols/abbreviations/acronyms/initialisms . . . . . . . . . . . . . . . . . . 34

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List of figures

Figure 1: Noise rating (NR) curves (adapted from STANAG 4293 and Screen Solutions, UK). . . 2

Figure 2: Acoustic test fixture (left) and sound level meter (right) used for noise measurements. . 5

Figure 3: Sea state time history during the trial. . . . . . . . . . . . . . . . . . . . . . 6

Figure 4: Instantaneous noise levels (1 second intervals) in the Ops Room during a period when drills were conducted. The left and right ear levels were measured with an ATF. . . 10

Figure 5: Instantaneous noise levels (1 second intervals) on the Bridge during force protection drills. The left and right ear levels were measured with an ATF. . . . . . . . . . 11

Figure B.1: Bridge noise levels by hour calculated as the average of 10-min LAeq values. . . . 29

Figure B.2: Ops Room noise levels by hour calculated as the average of 10-min LAeq values. . . 30

Figure B.3: CCR noise levels by hour calculated as the average of 10-min LAeq values. . . . . 31

Figure B.4: MCR noise levels by hour calculated as the average of 10-min LAeq values. . . . . 32

Figure B.5: 1/3 octave band spectra averaged over 24 hours in the Bridge, Ops Room, CCR and MCR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

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List of tables

Table 1: Speech Interference Levels (SIL)in dB, adapted from NATO STANAG 4293 Annex C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Table 2: 24-hour noise data in critical control spaces, ranges based on averages of equivalent sound pressure levels (LAeq) taken over consecutive 10-minute intervals. . . . . . . 8

Table 3: Speech interference level (SIL) and noise rating (NR). . . . . . . . . . . . . . . 8

Table 4: Expected voice levels based on SIL. . . . . . . . . . . . . . . . . . . . . . 9

Table 5: Instantaneous headset noise measured in-ear and ambient noise levels in the Ops Room and Bridge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Table 6: Sample daytime readings in various spaces around the ship during quiet watch, sea state 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Table B.1: Maximum noise levels in shipboard spaces (adapted from NATO STANAG 4293). . 28

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Acknowledgements

The authors would like to acknowledge the RCN Crewing and Human factors project sponsor, D Nav P&T, and project stakeholder DNCI, especially Cdr Plaschka. This work would not have been possible without the outstanding support of the commander and crew of HMCS Montreal: Cdr Sherban, CPO1 Ryan, Lt(N) Fernandez, Lt(N) Monette and PO1 O’Brien.

The authors would also like to acknowledge Dr. Renee Chow for her support in initiating the study and her contribution to the design of the voice communication questionnaire. Dr. James Karle is acknowledged for his support of the experimental team during the sea trial.

DRDC-RDDC-2018-R156 1

1 Introduction

1.1 Background

As part of the efforts to support ongoing acquisition projects for the Royal Canadian Navy (RCN), Defence Research and Development Canada (DRDC) is conducting research within the crewing and human factors project. One aspect of the project is to investigate human factors issues as they relate to critical control spaces and human performance on current naval platforms to provide guidance on the layout design of future platforms. DRDC is developing its current modeling capability to evaluate the layout designs of critical control spaces. In layout design, there are four domains of focus in communication analysis: auditory, visual, tactile and distance (Hendy, Berger & Wong, 1989). Until recently, the auditory domain has been based on the input of a single number (noise level) without knowledge of how the noise levels vary on the ship or what the expected speech communication effectiveness would be in that noise.

Effective communication between RCN members in critical control spaces at sea is required for mission success. Communication can occur through the use of radio systems or face-to-face. Constant background noise from machinery and intermittent high-level noise from weapon fire and aircraft flyovers can interfere with voice communication. These non-verbal interferences make it difficult to hear speech, causing energetic masking of communication (Brungart, 2001). Conversations between operators in the room and transmissions from unattended radio channels are distracting sources that cause informational masking of communication. Both background noise and distracting non-attended speech must be considered in the study of voice communication. Headsets that are worn in-ear or over the ears (earmuff style) can attenuate ambient sounds. This could be advantageous for listening to radio transmissions, but at the same time can hinder face-to-face conversations. This report describes noise measurements from the Communication in Critical Control Spaces trial on the HMCS Montreal “X-ship.” It was supported by project 01ab, RCN crewing and human factors.

1.2 Objectives

The objective of the current study was to measure ambient noise levels in four critical control spaces of a modernized Halifax-Class patrol frigate: the Bridge, the operations room (Ops Room), the communications control room (CCR) and the machinery control room (MCR). An acoustic manikin was also used to monitor the noise levels produced at the ear by the communication headsets. The noise data was used to calculate speech interference levels and the expected vocal effort required to communicate in the control spaces. In addition to the noise measurements, questionnaires on communication and workplace satisfaction were administered, and some participants were followed up with interviews. Selected results from the communication questionnaire (Annex A) will be used in the discussion of the noise survey results. Detailed analyses of the questionnaires and interviews will be presented in separate reports.

1.3 Noise exposure and speech interference

Noise levels are expressed in units of decibels, sound pressure level (dB SPL) referenced to the lowest detectable sound in Pascals (20 μPa). While the range of human hearing is about 20 Hz to 20000 Hz, not all frequencies are heard equally. To reflect this, a frequency weighting is often used to de-emphasize low frequency sounds which cannot be heard at low levels and are therefore considered to be less harmful to

2 DRDC-RDDC-2018-R156

hearing. This frequency weighting, called the A-weighting, is about -50 dB at 20 Hz and gradually increases with frequency to reach 0 dB at 1000 Hz. The A-weighting is often applied when noise levels are expressed in terms of human exposure (dBA). The Canadian Standards Association (CSA) recommends that hearing protection be used when the noise level is 85 dBA or higher (CSA Z94.2-14), while the Canada Labour Code daily noise exposure limit is 87 dBA for 8 hours (Canada Occupational Health and Safety Regulations SOR/86-304, Part VII, 2017).

For noise onboard frigates, the North Atlantic Treaty Organisation (NATO) Standardisation Agreement (STANAG) 4293 (1990) provides guidelines for the acoustical environment in NATO surface ships. It stipulates that warning signs shall be posted in areas of the ship where the noise levels exceed 85 dBA and gives a table of recommended maximum noise levels (MNL) in different shipboard spaces. The MNL refers to the noise inside a space resulting from permanently installed equipment. The full listing of MNLs is provided in the Annex B, Table B.1. For most control rooms that are permanently occupied by personnel, the MNL is 60 dBA (line 11 of Table B.1), except for the engine control room and damage control room, which is 70 dBA (line 8 of Table B.1). When the MNL is exceeded, it is necessary to record the noise levels in octave bands from 31.5 to 8000 Hz to determine the Noise Rating (NR). The NR curves provided in Annex B of STANAG 4293 are represented in Figure 1 (adapted from Screen Solutions, UK). The maximum noise rating for control rooms is NR 55 (line 11 of Table B.1). It is noted that although STANAG 4293 references the International Organisation for Standardization (ISO) 1996-1 for the NR curves, they are not part of the current version of ISO 1996-1:2016.

Figure 1: Noise rating (NR) curves (adapted from STANAG 4293 and Screen Solutions, UK).


For auditory communication, the speech interference level (SIL) is calculated from the background noise levels at speech frequencies (500 to 4000 Hz) as

(1)

Where L0.5, L1, L2 and L4 are the sound pressure levels in the 500, 1000, 2000 and 4000 Hz octave bands, respectively. The SIL can then be used to estimate the vocal effort based on the distance between the talker and the listener (Table 1). For example, if the SIL (Eq.1) calculated from the background noise of a room is 58 dBA, Table 1 indicates that a normal voice could be used for a distance of 0.9 m, while raised and very loud voices would be required at distances of 1.8 m and 3.6 m.

The SIL as defined in Eq. 1 and Table 1 is consistent with the current American National Standard Institute/Acoustical Society of America (ANSI/ASA) standard, ANSI/ASA S12.65-2006. The ANSI/ASA standard also includes a figure for SIL that provides an estimate based on the total A-weighted noise level, which can be used if the octave band noise levels are not available for the calculation of SIL (Eq. 1). The voice levels are given as requirements for just-reliable communication, or 70% accuracy on a standardized speech intelligibility test.

Table 1: Speech Interference Levels (SIL)in dB, adapted from NATO STANAG 4293 Annex C.

Distance from listener (m)

Normal voice Raised voice Very loud voice Shouting

0.15 74 80 86 92

0.3 68 74 80 86

0.6 62 68 74 86

0.9 58 64 70 76

1.2 56 62 68 74

1.5 54 60 66 72

1.8 52 58 64 70

3.6 46 52 58 64

While the SIL is a useful tool for estimating communication effectiveness, it should be noted that its application is for face-to-face communication between individuals with normal hearing function in non-reverberant environments. Room acoustics factors, electronic transmission of speech and individual differences (e.g., degree of hearing loss, accent, fatigue, use of visual cues) can affect speech intelligibility in ways that are not predicted by the SIL (ANSI/ASA S12.65, 2006).


1.4 Previous work

It is apparent from the literature that communication and noise in critical control spaces has not been a focus of research. Previous studies have mainly focused on hearing loss among navy personnel. For example, data from the United States Navy Hearing Conservation Program Database from 1995 to 1999 were analyzed for effects of age, sex and military rank on significant threshold shift (STS) rates (Bohnker et al., 2004). Lower STS rates were found for women than for men, as well as for officers than for those enlisted members. The data also showed an increase in STS rates with increasing age. Similarly, Trost (2007) looked at hearing test records of enlisted navy personnel from 1979 to 2004 to identify postings of higher risk for hearing loss. From analyzing nearly 268,000 records, it was concluded that an increased probability of hearing loss was associated with a longer time spent on board surface warships. A potential confounding factor for hearing loss is the combined effect of noise and ototoxic solvent exposure which has been reported previously by military personnel (Abel, 2005).

Although hearing loss has been associated with ship time, few studies have reported noise data collected in situ. One study conducted by Paddan measured the noise levels on a HMS Grimsby (2016) during firing of a heavy machine gun. The measurements were taken at multiple locations on or near the Bridge. The highest peak sound pressure levels measured ranged from 112.8 dBC to 160.7 dBC (the C-weighting does not de-emphasize low-frequency sounds) while the highest sound exposure levels measured ranged from 80.5 dBA to 127.8 dBA. The noise data indicated that the operator of the weapon must wear hearing protection during firing. However, the effects of gunfire on the noise levels in other occupied areas on the ship were not measured. Few studies have reported noise levels in critical control spaces and living areas. A study of various Royal Norweigian Navy vessels found average noise levels of 56.0, 59.1 and 62.9 dBA on frigates in the Bridge, operations room and radio room, respectively (Sunde et al., 2015). For RCN platforms, only one report of a noise survey was found (Crabtree, 1975). Noise measurements were conducted on the HMCS Iroquois. The overall noise levels throughout the Ops Room ranged from 69 to 78 dBA (decibels, A-weighted). The Bridge was the least noisy of all the operational areas at 64 dBA, which was said to be acceptable for face-to-face speech communication up to six feet. The report concluded that the ambient noise levels should not affect operations, as long as noise-attenuating headsets were worn in the noisier areas such as the engine rooms.

Ambient noise levels and distance between collaborators are key factors that affect face-to-face communication, but they do not predict communication effectiveness when headsets are used. Keller et al. (2017) studied communication effectiveness in a simulated naval command and control environment. Response error rates, requests for repeats and failures to respond significantly increased with decreasing signal-to-noise ratios (SNR), which mapped to speech intelligibility (SI) scores from 40 to 100%. Importantly, there was a significant increase in communication errors between SI scores of 60 to 80%, suggesting a critical value for SI in that range. This was consistent with the ANSI/ASA S12.65-2006 criteria of 70% SI for just-reliable communication.

Based on our previous recommendations for requirements for modeling auditory communication (Nakashima et al., 2015), we designed a noise survey and communication study for the RCN Experimental Ship, the HMCS Montreal. To our knowledge, this was the first of this type of data collection on a modernized Halifax-class frigate.


2 Materials and methods

2.1 Apparatus

Ambient noise levels were logged using Larson-Davis Type 1 sound levels meters (models LxT and 831). Communication headset noise levels were logged with a GRAS 45CB acoustic test fixture (ATF) manikin head, connected to a Sinus Soundbook data acquisition system. The ATF and a sound level meter are shown in Figure 2.

Figure 2: Acoustic test fixture (left) and sound level meter (right) used for noise measurements.

2.2 Procedure

The experimental protocol, which included the noise measurements, questionnaires and interviews, was approved by the DRDC Human Research Ethics Committee (HREC) (protocol 2015-038). The study was conducted on the HMCS Montreal during a seven-day sea trial from 12 to 18 February 2017. The weather was particularly stormy during the trial, resulting in challenging sea states as shown in Figure 3. Helicopter landing operations (flying stations) were conducted throughout the trial. Since the timing of the flying stations was dependent on the weather and sea state, it was difficult to account for these factors when setting up the noise measurements.

A sound level meter was used to log noise data in the Bridge, Ops Room, CCR and MCR for one 24-hour period. The start and end times of each 24-hour data collection period are shown with the sea state data in Figure 3. The sound level meter was placed at the Commanding Officer’s (CO) chair on the Bridge, in front of an Ops Room officer (ORO) workstation in Ops Room, near a computer network workstation in the CCR and on a maintainer’s console at the back of the MCR. The Bridge and CCR were measured during rough seas (sea states 3 to 6) relative to when the Ops Room and MCR were measured (sea states 1 to 3). Due to equipment limitations, it was not possible to conduct the measurements concurrently. The sound level meter was programmed to log total (dB SPL and dBA) and 1/3 octave-band noise levels at 1 second


intervals, as well as equivalent A-weighted levels (LAeq) every 10 minutes. The LAeq is the time-averaged, A-weighted sound pressure level over the measurement period (International Electrotechnical Commission, IEC 61672-1, 2013).

The ATF was used to log noise levels from a communication headset (Sennheiser ASG NAVCOM-46) on the Bridge during a flying station for about 2 hours, and in the Ops Room during drills for about 90 minutes. In both cases, the headsets were configured for listening to maximum radio traffic, at maximum volume, and a reference microphone was used to simultaneously log the ambient noise levels. Additional measurements included 30-second samples of noise levels in the officers’ mess, chiefs’ and petty officers’ mess, one non-commissioned members’ mess (sleeping quarters) and selected corridors throughout the ship.

Figure 3: Sea state time history during the trial.

Crewmembers who worked in one or more of the control rooms of interest were asked to complete a 30-question voice communication questionnaire (Annex A). While detailed analyses and discussion of the questionnaire responses will be presented in a separate report, selected results that are relevant to the noise data will be included in the discussion. In particular, responses about the use of non-verbal cues to aid communication, perceived effort to communicate, requirement for repetition, and sources of noise interference will be discussed for each of the four control rooms.


2.3 Data analysis

For each 24-hour data collection period, equivalent A-weighted noise levels (Leq, dBA) and 1/3 octave band spectra were logged with the sound level meter for 10-minute periods. The decibel average of the Leq levels were calculated for each hour and the entire 24-hour period. The 24-hour decibel average was used to calculate the SIL (Equation 1) and the NR (Figure 1) for assessment against the STANAG 4293 limits for control spaces. It should be noted that although the 24-hour decibel-averaged noise level is useful for understanding speech interference, it is not representative of total noise exposure, which is cumulative over time.

When analyzing the headset noise levels, it must be noted that noise measured in-ear is elevated compared to ambient noise measurements due to the transfer function of the ear (i.e., ear canal resonances). In-ear noise levels are not equivalent to noise exposure, which is calculated from the ambient noise level. While a procedure for estimating headset noise exposure from the in-ear levels exists (CSA Z107.56), in the current study the data were only logged during action stations which did not represent the entire duration of a work shift. Therefore, only ranges of noise levels were calculated to provide information about the levels produced during radio transmissions.


3 Results

3.1 Overall noise levels, speech interference and noise rating

The equivalent sound pressure levels, LAeq, over consecutive 10 min intervals were averaged over the 24 hour logging periods. The results are shown in Table 2, along with the ranges of the 10-minute LAeq in each of the four control rooms. While the maximum levels in each of the rooms were similar (76.3 to 77.5 dBA), the noise levels on the Bridge were considerably lower than the other rooms during times of quiet watch (52.0 dBA compared to 65.6–71.2 dBA). It was noted that the CCR had the highest average noise level at 72.1 dBA and also the smallest range. Importantly, the average noise levels in all of the control rooms exceed the STANAG MNL of 60 dBA. Hourly average noise levels are shown in Annex B, Figures B.1 to B.4. While the noise levels on the Bridge met the requirement during some of the 10-minute intervals as shown by the lower end of the range in Table 1, the hourly average levels shown in Figure B.1 are all greater than 60 dBA.

Table 2: 24-hour noise data in critical control spaces, ranges based on averages of equivalent sound pressure levels (LAeq) taken over consecutive 10-minute intervals.

Room 24-hr average (dBA)

Range (LAeq, dBA)

Bridge 62.6 52.0–77.3 Ops 69.8 66.2–78.8 CCR 72.1 71.2–76.3 MCR 71.1 65.6–77.5

To calculate the SIL (Equation 1) and the NR (Table 1), it is necessary to obtain the noise levels in octave bands. The octave band noise levels at speech frequencies (500 to 4000 Hz) are shown in Table 3 with the resulting SIL and NR. The NR requires noise levels at a broader range of frequencies (31.5 to 8000 Hz) which are shown in Annex B, Figure B.5. The CCR had the highest SIL (65.4) and NR (68) of the four control rooms. The NR for all four rooms exceeded the STANAG limit of 55, suggesting that auditory communication would be adversely affected. This is confirmed by the expected voice levels shown in Table 4 for speaker-listener distances of 0.9, 1.8 and 3.6 m. Based on the 24-hour average noise levels, raised voices would be required to communicate at 0.9m in the Ops Room, CCR and MCR. However, it should be noted that when the noise levels are at the highest (76.3 to 78.8 dBA based on the maximum 10-min averages shown in Table 2), shouting voices would be required at 0.9m in all four of the rooms.

Table 3: Speech interference level (SIL) and noise rating (NR).

Room Sound Pressure Level (dB SPL) 500 Hz 1000 Hz 2000 Hz 4000 Hz SIL NR

Bridge 58.8 56.6 55.3 50.9 55.4 58 Ops 67.9 63.8 61.1 55.7 62.1 65 CCR 65.3 68.1 64.5 63.7 65.4 68 MCR 68.5 65.8 63.8 59.2 64.3 66


Table 4: Expected voice levels based on SIL.

Room SIL Expected voice level based on 24-hr average SIL 0.9 m 1.8 m 3.6 m

Bridge 55.4 Normal Raised Raised Ops 62.1 Raised Very Loud Very Loud CCR 65.4 Raised Very Loud Shout MCR 64.3 Raised Very Loud Shout

3.2 Headset noise levels

Headset and ambient noise levels were logged during periods of high activity in the Ops Room (drills) and the Bridge (force protection exercise). The Ops Room instantaneous noise levels (1 second intervals) measured at the ears of the ATF and with an ambient microphone are shown in Figure 4. The equipment was set up to start logging at the time the drills were scheduled, but the data suggest that there was a delay, since a shift to higher noise levels is seen in the second half of the recording. Instantaneous in-ear levels exceeded 100 dB numerous times during the recording, reaching as high as 109.4 dBA. By contrast, ambient noise levels only reached 87.6 dBA.

The headset and ambient noise levels are shown in Figure 5 from the Bridge during force protection drills. In-ear noise levels reached as high as 108.7 dBA and ambient levels as high as 103.7 dBA. Ranges for the instantaneous noise levels during the Ops Room and Bridge drills are shown in Table 5. Note that noise levels measured in-ear are amplified compared to ambient levels due to ear canal resonances.


Figure 4: Instantaneous noise levels (1 second intervals) in the Ops Room during a period when drills

were conducted. The left and right ear levels were measured with an ATF.


Figure 5: Instantaneous noise levels (1 second intervals) on the Bridge during force protection drills.

The left and right ear levels were measured with an ATF.

Table 5: Instantaneous headset noise measured in-ear and ambient noise levels in the Ops Room and Bridge.

Room Duration *Left ear range (dBA)

*Right ear range (dBA)

Ambient range (dBA)

Ops 90 min 66.5–104.9 67.3–109.4 64.2–87.6

Bridge 170 min 66.9–108.7 66.7–107.8 61.9–103.7

*In-ear noise levels are amplified by ear canal resonances.


3.3 Noise levels in other areas

Sample noise readings (30-second LAeq) were recorded in several areas throughout the ship during quiet watch in sea state 5. The levels are shown in Table 6 along with STANAG 4293 limits for the associated space category (see Annex B, Table B.1 for details). All of the areas were within the STANAG limits at the time of measurement.

Table 6: Sample daytime readings in various spaces around the ship during quiet watch, sea state 5.

Location Sound Pressure Level (dBA)

STANAG 4293 limit

Comments

3 deck beside canteen 64.3 75 Treadmill in use, walking speed 3 deck beside canteen 67.7 75 Treadmill in use, running speed

3 deck chiefs’ and POs’ mess 63.3 65 Televisions on, less than 5 people inside

3 deck outside 10 mess 63.4 N/A 2 deck sonar section 61.5 70 2 deck officers mess 57.8 65 Television off, 2 people inside 2 deck outside of sick bay 54.2 60 2 deck inside 2 mess 47.5 60 Quiet, lights out


4 Discussion

4.1 Background noise levels and speech interference

The MNL for shipboard spaces listed in Annex B, Table B.1 refer to the noise produced by permanently installed equipment, and therefore do not include speech noise. It can be assumed that noise levels at the bottom of the ranges shown in Table 2 occurred when there were few occupants in the rooms and minimal talking. However, even the lowest noise levels that were recorded in the Ops Room, CCR and MCR exceeded the STANAG limit of 60 dBA. The ranges of ambient noise levels in the four control rooms were not high enough to cause concern for noise-induced hearing loss (Canada Occupational Health and Safety Regulations SOR/86-304, Part VII, 2017), but they were high enough to cause difficulties for auditory communication. The expected voice levels listed in Table 4 indicate that based on the average noise levels, raised voices are required at a very short distance (0.9m) to communicate in the Ops Rooms, CCR and MCR. Noise levels in the CCR and MCR were not reported in previous studies (Crabtree, 1975 and Sunde et al., 2015).

The CCR was the worst for auditory communication, not only because it had the highest average noise level (72.1 dBA) and NR (68), but because the ambient noise never decreased. While the three other rooms had periods of quieter levels, presumeably due to low activity (Table 2 and Annex B, Figures B.1 to B.4), the noise levels in the CCR were consistent throughout the 24-hour measurement period. It is assumed that the elevated noise levels were due to the computer servers and equipment and were not affected by the relatively high sea states (4 to 6 as shown in Figure 3). Similarly elevated noise levels were not observed in the bridge, which was measured during comparable sea states (although not simultaneously with the CCR). Operators in the CCR would not only have difficulty communicating between adjacent work stations (raised voice required at a small distance of 0.9 m), they are also potentially at risk for noise-induced stress and fatigue. The wearing of linear-attenuation earplugs, such as a musician’s earplug, could potentially reduce the annoyance of the constant server noise without further hindering auditory communication. Isolation of the noisy servers to an enclosed space, away from the work stations, would help to reduce the overall noise levels in the room.

The average noise level in the MCR was only slightly lower than the CCR at 71.1 dBA. However, the range of noise levels was larger (65.6–77.5 dB), indicating that the machinery noise did not dominate the environment during quiet watch. During periods of activity, it was observed that there were a number of auditory alerts that added to the ambient noise, and that there were a number of crewmembers occupying a relatively small space. Since we were unable to find previous work that described noise levels or communication requirements in the MCR (i.e., if communication headsets are used and which operators need to communicate within the room), it is difficult to comment on the impact of the increased noise levels on operator performance. Some of the questionnaire findings from the MCR participants will be discussed in Section 4.3.

The range of noise levels in the Ops Room was similar to those in the MCR. During quiet watch, a walk-through noise assessment with the sound level meter in-hand found levels of about 65 to 68 dBA throughout the room, which is in agreement with the low end of the noise range shown in Table 2 (66.2 dBA). During period of high activity, for example during the drills when the communication headset was monitored, 10-min LAeq levels reached 78.8 dBA and peak (instantaneous) levels reached 87.6 dBA. By contrast, Crabtree (1975) reported that Ops Room noise levels on the HMCS Iroquois


differed by less than 1 dB during quiescent and operational times, although the noise levels were reported to range from 69 to 78 dBA throughout the room. In the current study the sound level meter was kept in the same location for the 24-hour logging period (in front of the ORO workstation). The location was chosen to capture noise from the frequent communications between the ORO and the Ops Room supervisor (ORS), who walks in front of officer workstations. The levels were generally much higher than the 55.1 to 62.1 dBA range reported for Royal Norwegian Navy frigates (Sunde et al., 2015), although the latter readings were from 15-second sample readings rather than 24-hour logs. It was observed in the current study that the room temperature was maintained at a lower level than other rooms on the ship, and that the air conditioning outlets contributed to the baseline ambient noise. If such low air temperatures are not required, a reduction in air conditioning could lower the ambient noise levels. During action stations when communication headsets are frequently used, noise-attenuating headsets could be helpful in reducing interference from unattended speech. In particular, electronic headsets that allow the wearer to control the volume of noise sampled from their surroundings would allow operators to block out ambient noise when they need to concentrate on radio traffic, and increase the ambient volume when they need to attend to face-to-face commands.

The Bridge was the quietest of the four spaces that were measured, with an average noise level of 62.6 dBA. While this is higher than the STANAG limit of 60 dBA, it does not cause concern for auditory communication over short distances (see Table 4). This finding is consistent with the HMCS Iroquois study which the Bridge noise level (64 dBA) was found to be acceptable for communication distance up to six feet (Crabtree, 1975). The lower end of the noise range was similar to that of the Norwegian frigate data (54.4–58.3 dBA; Sunde et al., 2015). Similar to the Ops Room, noise-attenuating headsets with ambient volume control could be useful during action stations when communication between the Bridge and Ops Room are frequent. However, not all crewmembers on the Bridge would be locked into a headset. For example, face-to-face communication between the officer of the watch (OOW) and the helmsman could be difficult during noisy periods due to their separation distance.

4.2 Communication headset noise

Noise levels from communication headsets were logged to provide information about the amount of activity on the radio channels and the noise levels that are produced at the ear. Unfortunately, we were unable to record the radio transmissions due to security reasons and thus were unable to analyze the data to distinguish utterances from various nets or assess the clarity of the transmitted messages. The headsets were configured to receive the maximum number of nets during the data logging periods in the Ops Room and Bridge, and the radio volume was maximized. With this configuration, in-ear noise levels reached as high as 109.4 dBA, and there were multiple occurrences of noise over 100 dBA (Figures 4 and 5). While noise levels measured in-ear are higher than the equivalent ambient levels due to ear canal resonances, they are potentially high enough to cause hearing damage over time. The evaluation of hearing damage risk for an individual crewmember at sea, however, would require a comprehensive monitoring of their noise exposure from headsets and ambient noise throughout the day. Further insight into headset use and communication effectiveness will be obtained from the communication questionnaire.

4.3 Hearing conservation

Although noise-induced hearing loss was not a focus of this study, the literature indicates that it is a common problem among ship crewmembers. Noise exposure, particularly in combination with solvent exposure, can cause hearing damage (Abel, 2005). It is well-known that higher SNR is required for


speech understanding for those with hearing impairment. The expected voice levels shown in Table 4 only apply to those with normal hearing. We did not measure noise levels in the engine rooms and other noisy areas of the ship due to operational limitations. However, it was seen from the communication headset data that operators who frequently use the headsets are potentially exposed to high noise levels.

It was observed during the small arms shoot that shooting personnel and others on the Bridge wings obtained earplugs from inside the Bridge. The shooters were required to listen to commands through the communications headset. If earplugs are worn with the headset, the shooter might have difficulty hearing and understanding commands, especially if they have pre-existing hearing loss. However, the communication headsets do not provide noise protection when used alone, as the earcups sit on the pinnae and do not form an acoustic seal over the ears. The use of noise-attenuating communication headsets is recommended for members during exposure to high-level noise.

4.4 Voice communication questionnaire

Results from the voice communication survey provided some insight about the impact of noise in these control spaces on inter-operator communication effectiveness. While the full results of the communication survey are documented elsewhere, a few highlights of the findings that are relevant to the noise measurement results are presented below.

A total of 64 crew members participated in the communication survey. They all worked in one of the ship’s four control spaces. Based on their responses, one third of them (33%) reported experiencing strain to follow a conversation in their workplace and 45% of them said they sometimes asked others to repeat during face-to-face interaction. The background noise was a general issue in all control spaces and was identified as the top factor that interfered with voice communication. Its impact was reported by 81% and 65% of all participants on either face-to-face or technology-mediated communication, respectively. However, there exist differences in the sources and levels of noise disturbance across control spaces.

Degradation in voice communication was more pronounced in the CCR than other control spaces. For face-to-face interaction, the percentage of CCR participants who reported experiencing strain to understand voice conversations and needing to ask others to repeat was 75%. By contrast, the global averages from all participants were 33% and 45% for these two measures, respectively. When participants were asked about the need to see a collaborator’s face for communication, 56% of CCR participants indicated such a requirement, higher than the global average of 27% from all. Unattended conversation from others was identified by 75% of CCR participants as an interfering factor to their own face-to-face interaction, and the global average was 56%. These results are consistent with the findings from the noise survey. The relatively high background noise level from equipment in the CCR leads to elevated vocal effort in voice conversation, both of which have a negative impact on communication effectiveness. To compensate for the noise interference, operators in the CCR rely more heavily on non-verbal cues like facial expressions during communication.

A unique characterization of the MCR is the frequent occurrence of auditory alerts from system alarms. Of the MCR participants, 58% reported that alarms were used one or more times each hour, compared to the 18% global average from all participants. Despite the frequency of alarms and moderate level of background noise, a modest proportion of MCR participants (25%) reported strain during face-to-face conversation when compared to the CCR (75%).


Results for the Ops Room and Bridge were similar. In addition to face-to-face conversation, technology-mediated communication plays a significant role in these two workplaces. The use of voice networks and headsets helps to control the overall noise levels in the rooms. Although the noise levels in both spaces still exceed the STANAG recommendation, their impact on voice communication effectiveness was less severe than the CCR. For example, 73% and 61% of participants in the Bridge and Ops Room reported no strain to follow face-to-face conversation, in contrast to 25% from the CCR.


5 Conclusion

To our knowledge, this is the first report of noise levels and auditory communication on a modernized CPF. Based on our study of four critical control spaces, we conclude that:

1. The average noise levels measured in the Bridge, Ops Room, CCR and MCR exceeded the STANAG 4293 limits for control spaces. While this could have a negative effect on auditory communication, the levels are not high enough to warrant the use of hearing protection.

2. The average noise levels in the CCR were the highest of the four control spaces, and the corresponding speech interference level suggests that increased vocal effort would be required at short distances. The presence of constant, moderate level noise could hinder crew performance by causing increased levels of stress and fatigue. As a short-term solution, linear-attenuation earplugs could be used to reduce the noise annoyance without hindering communication. In future designs of the CCR, the servers should be enclosed and isolated away from the workstations to minimize noise disturbance.

3. While the ambient noise levels in the Bridge and Ops Room were not excessive during quiet watch, headset use should be further investigated. When configured to listen to multiple radio channels at the maximum volume, the at-ear noise levels were high enough to cause concern for headset noise exposure. Future studies should investigate the extent of headset use and volume to determine whether or not limitations should be placed to minimize the risk of hearing hazard.

4. Results from this study support design and evaluation of critical control spaces on future RCN platforms, particularly the use of modeling and simulation for workplace layout optimization. With information about noise levels during quiet watch and action stations, the auditory links in the model can be more realistically represented.

Importantly, we identified noise and communication issues in the CCR that have not been previously reported. Other studies on CPFs and other warships have focussed on the Bridge and Ops Room, in which minimal concerns regarding communication interference have been reported.


References

Abel, S. M. (2005). Hearing loss in military aviation and other trades: investigation of prevalence and risk factors. Aviat Space Environ Med, 76:1128–35.

American National Standards Institute/Acoustical Society of America, ANSI/ASA S12.65-2006(R2011). For rating noise with respect to speech interference. New York, New York.

Bohnker, B. K., Page, J. C., Rovig, G. W. et al. (2004). Navy hearing conservation program: 1995–1999 retrospective analysis of threshold shifts for age, sex, and officer/enlisted status. Military Medicine 169(1):73–76.

Brungart, D. S. (2001). Informational and energetic masking effects in the perception of two simultaneous talkers. The Journal of the Acoustical Society of America, 109(3):1101–1109.

Canada Occupational Health and Safety Regulations (SOR/86-304), Part VII – Levels of sound. http://laws-lois.justice.gc.ca/eng/regulations/SOR-86-304/index.html, accessed 22 Nov 2017.

Canadian Standards Association Z107.56-13 (2013). Measurement of noise exposure. Mississauga, ON.

Canadian Standards Association Z94.2-14 (2014). Hearing protection devices – Performance, selection, care and use. Mississauga, ON.

Crabtree, R. B. (1975). A noise survey of the HMCS IROQUOIS. DCIEM Technical Report no. 76-X-26.

Hendy, K. C., Berger, J., and Wong, C.C. (1989). Analysis of DDH280 Bridge activity using a computer-aided workspace layout program (LOCATE). DCIEM No. 89-RR-18.

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International Organisation for Standardization, ISO 1996-1:2016. Acoustics – Description, measurement and assessment of environmental noise – Part 1: Basic quantities and assessment procedures.

Keller, M. D., Ziriax, J., Barns, W. et al. (2017). Hearing Research, 349:55–66.

Nakashima, A., Chow, R., and Wang, W.. (2015). Research requirements for modelling of auditory communications in critical control spaces on RCN platforms. Defence Research and Development Canada, Science Report, DRDC-RDDC-2015-R171.

NATO STANAG 4293 (edition 1) 1990. Guidelines for the acoustical environment in NATO surface ships.

Paddan G. (2016). Occupational noise exposure on a Royal Navy warship during weapon fire. Noise and Health 18(84):266–273.


Screen solutions, East Sussex, UK. Noise Rating (NR). http://www.acousticcomfort.co.uk/uploads/Noise%20Ratings.pdf, accessed 1 Dec 2017.

Sunde, E., Irgans-Hanse, K., Moen, B. E., et al. (2014). Noise and exposure of personnel aboard vessels in the Royal Norwegian Navy. Annals of Occupational Hygiene, 59(2):182-199.

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Annex A Voice communication questionnaire

The following survey was completed by crewmembers who worked in one or more of the control rooms included in this study.


Annex B Supplementary data

Table B.1: Maximum noise levels in shipboard spaces (adapted from NATO STANAG 4293).

Space category Maxmium noise (normal cruising)

dBA NR

1. Medical spaces (sick bay) 60 55 2. Berthing areas 60 55 3. Messrooms 65 60 4. Offices, libraries 65 60 5. Galley/pantry, gym, washrooms, stores 75 70 6. Engine/auxiliary machinery rooms 7. permanently occupied by personnel, control stations in room

90 85

7. Engine/auxiliary machinery rooms temporarily occupied by personnel for inspection purposes, control station outside the room

110 105

8. Central engine and damage control rooms 70 65 9. Workshops except electronic workshops 80 75 10. Electronic workshops 70 65 11. *Ship control station (pilot house), fire control room, combat information center and adjoining rooms belonging to CIC and occupied by personnel, sonar control room, electronic counter measure room

60 55

12. Spaces for communication navigation and detection equipment (not permanently occupied by personnel)

70 65

13. Bridge wings 70 65 14. Weather deck stations permanently occupied by personnel

75 70


Figure B.1: Bridge noise levels by hour calculated as the average of 10-min LAeq values.


Figure B.2: Ops Room noise levels by hour calculated as the average of 10-min LAeq values.


Figure B.3: CCR noise levels by hour calculated as the average of 10-min LAeq values.


Figure B.4: MCR noise levels by hour calculated as the average of 10-min LAeq values.


Figure B.5: 1/3 octave band spectra averaged over 24 hours in the Bridge, Ops Room, CCR and MCR.


List of symbols/abbreviations/acronyms/initialisms

ANSI American National Standards Institute

ASA Acoustical Society of America

ATF Acoustic Test Fixture

CCR Communications Control Room

CSA Canadian Standards Association

dB SPL Decibels, Sound Pressure Level

dBA Decibels, A-weighted

dBC Decibels, C-weighted

DRDC Defence Research and Development Canada

HMCS Her Majesty’s Canadian Ship

HREC Human Research Ethics Committee

Hz Hertz, unit of sound frequency

IEC International Electrotechnical Commission

ISO International Organisation for Standardisation

LAeq Time-averaged, A-weighted Sound Pressure Level

MCR Machinery Control Room

MNL Maximum Noise Level

NATO North Atlantic Treaty Organization

NR Noise Rating

OOW Officer of the Watch

Ops Room Operations Room

ORO Operations Room Officer

ORS Operations Room Supervisor

RCN Royal Canadian Navy

SI Speech Intelligibility

SIL Speech Interference Level

SNR Speech-to-Noise Ratio

STS Standard (hearing) Threshold Shift

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1. ORIGINATOR (Name and address of the organization preparing the document. A DRDC Centre sponsoring a contractor's report, or tasking agency, is entered in Section 8.) DRDC – Toronto Research Centre Defence Research and Development Canada 1133 Sheppard Avenue West P.O. Box 2000 Toronto, Ontario M3M 3B9 Canada

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3. TITLE (The document title and sub-title as indicated on the title page.) Noise levels in critical control spaces aboard a modernized Halifax-class patrol frigate: Implications for communication effectiveness

4. AUTHORS (Last name, followed by initials – ranks, titles, etc., not to be used) Nakashima, A.; Wang, W.; Cai, J.

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12. KEYWORDS, DESCRIPTORS or IDENTIFIERS (Use semi-colon as a delimiter.)

noise; communication; hearing

13. ABSTRACT (When available in the document, the French version of the abstract must be included here.)

As part of ongoing efforts to investigate human factors issues that affect human performance on current naval platforms, a noise survey and communication study was conducted on the HMCS Montreal. The results will provide guidance on the optimization of layout within critical control space on future naval platforms. The average noise levels in four critical control spaces, the Bridge, operations room, communications control room (CCR) and machinery control room (MCR), exceeded the North Atlantic Treaty Organisation (NATO) Standardisation Agreement (STANAG) 4293 limits. The noise levels were the highest in the CCR, indicating that increased vocal effort is required to communicate over short distances. The questionnaire results indicated that CCR crewmembers had more difficulty with face-to-face communication than crewmembers in other control rooms. Noise levels logged from the communication headsets in the Bridge and operations room were high enough to cause concern for headset noise exposure when the headset was at full volume. The results provide information about noise levels during quiet watch and action stations in four critical control spaces, which will support modeling and simulation efforts for workplace layout optimization.

Dans le cadre des efforts continus visant à étudier les facteurs humains qui influent sur la performance humaine sur les plateformes navales actuelles, une étude sur le bruit et les communications a été menée à bord du NCSM Montréal. Les résultats orienteront l’aménagement optimisé des espaces de contrôle critiques des futures plateformes navales. Les niveaux de bruit moyens dans quatre espaces de contrôle critiques (c.-à-d. la passerelle, la salle des opérations, la salle de contrôle des communications [SCC] et la salle de contrôle des machines [MCR]) dépassaient les limites de l’accord de normalisation (STANAG 4293) de l’Organisation du Traité de l’Atlantique Nord (OTAN). Les niveaux de bruit les plus élevés étaient dans la SCC, ce qui indique qu’il faut parler plus fort pour communiquer sur de courtes distances. Les résultats du questionnaire démontrent que les membres d’équipage de la SCC ont plus de difficulté à communiquer en personne que les membres d’équipage des autres salles de contrôle. Les niveaux de bruit enregistrés à partir des casques d’écoute de la passerelle et de la salle des opérations étaient suffisamment élevés pour entraîner des problèmes d’exposition au bruit lorsque le casque d’écoute est à plein volume. Les résultats fournissent également de l’information sur les niveaux de bruit dans quatre espaces de contrôle critiques pendant les heures creuses des postes de surveillance et de combat, ce qui appuiera les efforts de modélisation et de simulation pour l’optimisation de l’aménagement du lieu de travail.

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