View/Download PDF
Buy Reprints
PDF

Translate this page into:

Original Article (Field Study)
61 (
2
); 48-56

Noise Survey at Naval Air Stations: A Novice Approach to an Old Problem

Sr Advisor (Aerospace Medicine), IAM, IAF
Classified Specialist (Aerospace Medicine), HoD, Dept of High Altitude Physiology and Hyperbaric Medicine, IAM, IAF
Sr Advisor (ENT) and Head, Dept of ENT, INHS Asvini

Abstract

Introduction:

Naval personnel who are working in various air stations, ships and aircraft carrier are regularly being exposed to high level of aircraft noise. Studies have indicated that noise induced hearing loss affects 25 to 80% of crew depending on their length of exposure to aircraft noise. Presently, the aircrew, ground crew and other support staff who constitutes the major risk group are not effectively monitored for primordial prevention from the deleterious effects of noise. Lack of health awareness, improper use of Hearing Protection Devices (HPDs), inadequate health monitoring system has made the issue more critical. In this study a novice attempt was made to carry out the noise survey in the naval air stations by employing Sound Level Meter (SLM).

Methods:

One fighter squadron, one transport squadron and two helicopter squadrons were selected for the noise survey. Sound Level Meter (Model-Pulsar 33) was used for collecting the noise data. A protocol was followed to determine the noise load at various occupational posts during various phases of air operations by measuring the “Equivalent Noise Level (Leq)”. Parameter LAt, which was representative of Equivalent Noise Level (Leq) was recorded at different occupational posts during the flying. A total of 93 occupational posts in 03 different air stations were surveyed for assessing the noise level and use of HPDs by the duty personnel at these posts. These occupational posts were categorized as per the level of noise and its safety standard recommended by NIOSH.

Results:

Of 93 occupational posts there were 48 (51.6 %) posts, which were found to be Noise Hazardous Posts where the noise level ≥ 85 dBA. At these 48 posts there were 11(22.9 %) posts where duty personnel were not using any kind of HPDs and 13 (27 %) posts where duty personnel were not using the appropriate HPDs. This study indicated that the compliance rate of adopting effective hearing protection was approximately 50%. The compliance rate of adopting effective noise protection methods were 8.3 % (aircraft dispersals), 33.3 % (hanger and open areas/verandah of squadrons), 50 % (squadron offices), 66.6 % (neighbouring squadrons, Ground Traffic Controller’s posts and Take-off end of runway) and 100 % (bird shooter’s location and ATC dispersals). Double Protection which is an effective means of protecting the worker at the aircraft dispersals or any other location where the noise level is ≥100 dBA is poorly adhered (01 against the requirement at 15 posts) to the noise safety.

Conclusions:

This survey indicates that there exists a need for using “Double Protection” by all duty personnel employed in the dispersals during air operations involving various naval aircrafts.

Keywords

Noise Induced Hearing Loss (NIHL)
Noise Mapping
Sound Level Meter (SLM)
Hearing Protection Devices (HPDs)
Double Protection

Introduction

Naval personnel who are working in various air stations, ships and aircraft carrier are regularly being exposed to high level of aircraft noise. Studies have indicated that noise induced hearing loss affects 25 to 80% of crew depending on their length of exposure to aircraft noise [1,2,3]. Noise Induced Hearing Loss (NIHL) is an almost entirely preventable disability. Identification of hazardous noise areas in the air stations; stratifying the occupational categories of service personnel and monitoring their hearing acuity by conducting regular audiometric testing; providing them the training on the benefits of hearing protection; enforcing the use of personal protective equipment; administrative measures such as shorter work shifts in noise hazardous environments; and engineering controls are the key areas that need deliberation as a hearing conservation program for the naval personnel involved in flying duties.

Presently, the aircrew, ground crew and other support staff who constitutes the major risk group are not effectively monitored for primordial prevention from the deleterious effects of noise. Lack of health awareness, improper use of Hearing Protection Devices (HPDs), inadequate health monitoring system has made the issue more critical. As a result, there has been an increasing concern about the safety and health aspects of excessive exposure to noise in routine air operations. This study was undertaken to carry out a noise survey of various occupational posts in naval air stations with the aim of determining the amount (in dB) of protection required to limit the risk of noise induced hearing loss among naval personnel exposed to aircraft noise in these stations.

Material and Methods

Selection of Air Station

The naval aircraft inventory consists of fighter jets, transport / Maritime Reconnaissance (MR) aircraft and helicopters. Two fighter squadrons, Two transport squadrons and two helicopter squadrons were selected for the noise survey. Approval of Administrative authority of Navy was obtained prior to conduct of the study. The aviation medicine specialists along with a medical staff of the respective air stations were associated in the study to collect the noise data.

Equipment employed

A Sound Level Meter (Model-Pulsar 33) was used for collecting the noise data. The equipment used was in compliance with the international standards i.e. IEC 60651, IEC 60804 and IEC 61672 and their European counterparts EN 60651 and EN 60804. This model also complied with American standards ANSI S1.4 and ANSI S1.43. Following calibration and settings were carried out prior to its use: -

  1. Calibration. MODEL 33 was calibrated before beginning a measurement by using a calibrator (MODEL100B) and its sensitivity was adjusted to 94dB. For all measurements, the MODEL 33 was set to read 93.7dB and it was ensured that, if the value of the reading differed more than + 0.3 dB from the calculated value, the sound level meter sensitivity needed adjusting.

  2. Setting. Before beginning a measurement in sound level meter mode, three functions (F1, F2 and F3) and integration time (T) were configured to frequency weighting (A, C or D), time weighting (F, S or I) and the T integration time was configured by selecting ‘time’ units in seconds, minutes and hours. Noise data in the air stations was collected in a typical configuration of F1 for LAF (A weighted sound level-fast), F2 for LAt (time average sound level) and F3 for LCpeak (C weighted peak) sound level.

Procedure

  1. Preliminary Preparations. The preliminary preparation includes:-

    1. Visit of the flying squadron and its neighbouring work places for interaction with aircrew, ground crew and other personnel exposed to aircraft noise while on duty.

    2. Identifying noise hazard air operations and the locations where the crew are positioned during such operations.

    3. Discussion of the study protocol with administrative authorities for necessary clearance.

    4. Establishing a line of communication with the captain of the aircraft in order to obtain a noise data synchronized with engine parameter.

  2. Noise data (Equivalent Continuous Noise) recording Protocol. In order to get the noise load in a particular air operation, noise data (LAF, LAt and LAE) at various work places in and around the aircraft squadron was recorded during the entire period of the air operations.

  3. Data Collection. In order to determine the level of noise exposure of duty personnel at their respective occupational posts during flying, a 15 minutes noise sample was recorded. This sample noise which was representative of a noise profile of an air operation and was considered for determination of “Equivalent Noise Level (Leq)”[4]. The parameter LAt, which was the representative parameter of equivalent noise was recorded over 15 minutes by using Pulsar 33 (SLM).

  4. Data Analysis. Software “Pulsar Acoustic Toolbox” was installed in a PC/Laptop computer and the data from the memory of MODEL 33 was transferred by using RS-232 communication port. Later the data was analysed by using “Microsoft Excel” and a free version of Statistical Package.

Results

The level of noise at various occupational posts during flying was determined from a the 15 minute-recording of noise parameter (LAt) by using Pulsar 33 (SLM). The values for different aircraft at different air bases are tabulated in Table 1 & 2. In order to obtain the information about Hearing Protection Devices (HPDs) being used at various occupational posts during flying, a questionnaire-based survey was conducted on duty people in the air stations. The result of the survey as per the occupational posts in the squadrons and stations are tabulated in Table 3 & 4 respectively. The International (NIOSH) recommendation for occupational noise exposure is 85 decibels, A-weighted, as an 8-hr time-weighted average (TWA) (85 dBA) [4]. Exposure at and above this level are considered hazardous. The occupational posts which recorded the noise ≥ 85 dBA was listed in the Table 5.

Table 1.: Aircraft Noise level (LAt in dBA) at various Occupational Posts in the Naval Air Stations
Sl No Occupational Posts Occupational Categories of DutyPersonnel LAt over 15 min (in dBA) during Air Ops
Fighter Base Transport Base Helicopter Base
F1 F2 T1 T2 H1 H2
1 Dispersal (near Aircraft / within 15 m) Main Line Party 114.3 104.3 107.6 106.9 107.5 105.4
2 Dispersal (> 15 m) Stand/by Line Party 111.2 108.1 106.3 106.0 105.0 105.1
3 Hanger Ground Crew 104.1 97.9 87.6 90.3 89.0 96.0
4 Verandah Aircrew Ground crew 99.7 94.8 88.2 85.6 86.1 88.3
5 Squadron Office (Non-AC) Aircrew Ground crew 93.2 90.2 83.3 83 84.9 86.2
6 Squadron Office (AC) Aircrew Ground crew 84.3 82.3 80.6 80.2 80.2 86.2
7 Squadron Office (SoundProof) Aircrew Ground crew 82.3 Not Available

Fighter Aircraft Squadrons (F1, F2), Transport Aircraft Squadrons (T1, T2)

Helicopter Aircraft Squadrons (H1, H2)

Table 2.: Aircraft Noise level (LAt in dBA) at various Occupational Posts in the Naval Air Stations
Sl No Occupational Posts Occupational Categories of Duty Personnel LAt over 15 min (in dBA) during Air Ops
Fighter Base Transport Base Helicopter Base
F1 F2 T1 T2 86.6 85.9
1 ATC Dispersal(50 meter) Crash & Salvage 89.5 89.3 82.3 84.8 85.3 86
2 GTC Post (50 meter) Ground Traffic Controller 91 87.8 82.7 87.2 86.3 85
3 Runway-Take-Off End Ground Crew 91.2 87.3 79.6 86.3 Em Em
4 Runway-Glide Path End Ground Crew 79.3 75.6 75.5 73.8 NA
5 Runway- Bird Shooter Aircrew Ground crew 95.5 88 86.3 84.3 NA
6 Neighboring SquadronOffice Aircrew Ground crew 101.7(310Sqn) 88.3(552Sqn) 80 (‘O’Schl) 81.7(321Sqn) 82.9(321Sqn) 86.1(336Sqn)
7 ATC Office Complex Aircrew Ground crew 78.3 73.9 73.2 78.2 79 80.6
8 Station Briefing Room Aircrew Ground crew 72.5 70.6 70.5 71.1 73.4 71.9
9 MET Office Complex Met Staff 79.5 74.5 75.1 82.1 80.9 81.5
10 Station Admin Offices Officers & Sailors 73.7 71.5 72.5 81.3 80.7 80.1
Table 3.: Type of Hearing Protection used by Duty Personnel at various Occupational Posts in the Naval Air Stations
Sl No Occupational Posts Occupational Categories of Duty Personnel LAt over 15 min (in dBA) during Air Ops
Fighter Base Transport Base Helicopter Base
F1 F2 T1 T2 H1 H2
1 Dispersal (near Aircraft / within 15 m) Main Line Party Dp Em Em Em Em Em
2 Dispersal (> 15 m) Stand/by Line Party Em Em Em Em Em Em
3 Hanger Ground Crew Em Ep N Ep Ep Em
4 Verandah Aircrew Ground crew Em Ep N Ep Ep N
5 Squadron Office (Non-AC) Aircrew Ground crew N N N N N N
6 Squadron Office (SoundProof) Aircrew Ground crew N N N N N N
7 Station Briefing Room Aircrew Ground crew N Not Available
Em : Ear MuffEp : Ear PlugDp : Double Protection (both Ear Plug & Ear Muff)N : Not using any kind of Hearing Protector

Em : Ear Muff Ep : Ear Plug Dp : Double Protection (both Ear Plug & Ear Muff)

N : Not using any kind of Hearing Protector

Table 4.: Type of Hearing Protection used by Duty Personnel at various Occupational Posts in the Naval Air Stations
Sl No Occupational Posts Occupational Categories of Duty Personnel LAt over 15 min (in dBA) during Air Ops
Fighter Base Transport Base Helicopter Base
F1 F2 T1 T2 H1 H2
1 ATC Dispersal(50 meter) Crash & Salvage Em Em Em Em Em Em
2 GTC Post (50 meter) Ground Traffic Controller N N Ep Ep Em Em
3 Runway-Take-Off End Crew Ground N N Ep Ep Em Em
4 Runway-Glide Path End Ground Crew N N Ep Ep --
5 Runway- Bird Shooter Aircrew Ground crew Em Em Ep Ep
6 Neighboring SquadronOffice Aircrew Ground crew Ep (310Sqn) N (552Sqn) N (‘O’Schl) Ep (321Sqn) Ep (321Sqn) Ep (336Sqn)
7 ATC Office Complex Aircrew Ground crew N N N N N N
8 Station Briefing Room Aircrew Ground crew N N N N N N
9 MET Office Complex Met Staff N N N N N N
10 Station Admin Offices Officers & Sailors N N N N N N
Em : Ear MuffEp : Ear PlugDp : Double Protection (both Ear Plug & Ear Muff)N : Not using any kind of Hearing Protector

Em : Ear Muff Ep : Ear Plug Dp : Double Protection (both Ear Plug & Ear Muff)

N : Not using any kind of Hearing Protector

Table 5.: Noise Hazardous Occupational Posts in Naval Air Stations
Sl No Occupational Posts LAt over 15 min (in dBA) during Air Ops
Fighter Base Transport Base Helicopter Base
F1 F2 T1 T2 H1 H2
1 Dispersal (within 15 m) 114.3 104.3 107.6 106.9 107.5 105.4
2 Dispersal (15 -50 m) 111.2 108.1 106.3 106.0 105.0 105.1
3 Hanger 104.1 97.9 87.6 90.3 89.0 96.0
4 Verandah 99.7 94.8 88.2 85.6 86.1 88.3
5 Squadron Offices 93.2 90.2 83.3 83 84.9 86.2
6 Neighboring Squadrons 101.7 88.3 80 81.7 82.9 86.1
7 Runway (Bird Shooter) 95.5 88 86.3 84.3 85
8 Runway (T/O End) 91.2 87.3 79.6 86.3 86.3 85
9 GTC Post (within 50 m) 91 87.8 82.7 87.2 85.3 86
10 ATC Dispersal 89.5 89.3 82.3 84.8 86.6 85.9

A total of 93 occupational posts in 03 different air stations were surveyed for assessing the noise level and use of HPDs by the duty personnel at these posts. These occupational posts were categorized as per the level of noise and its safety standard recommended by NIOSH. Of 93 occupational posts, 48 (51.6 %) posts were found to be Noise Hazardous Posts having the noise level ≥ 85 dBA. The types of hearing protection devices used by the personnel while working in these occupational posts are listed in Table 6. Of these 48 posts, there were 11(22.9 %) posts where duty personnel not using any kind of HPDs and 13 (27 %) posts where duty personnel were not using the appropriate HPDs. This study indicated that the compliance rate of adopting effective hearing protection is only 50 %. The compliance rate of adopting effective noise protection methods were 8.3 % (aircraft dispersals), 33.3 % (hanger and open areas/verandah of squadrons), 50 % (squadron offices), 66.6 % (neighboring squadrons, Ground Traffic Controller’s posts and Take-off end of runway) and 100 % (bird shooter’s location and ATC dispersals). Double Protection which is an effective means of protecting the worker at the aircraft dispersals or any other location where the noise level is ≥100 dBA is poorly adhered (01 against the requirement at 15 posts) to the noise safety.

Table 6.: Use of various HPDs during Air Ops at Aviation Occupational Posts
Sl No Occupational Posts LAt over 15 min (in dBA) during Air Ops
Fighter Base Transport Base Helicopter Base
F1 F2 T1 T2 H1 H2
1 Dispersal (within 15 m) DP DP DP DP DP DP
Present Practice Dp Em Em Em Em Em
2 Dispersal (15 -50 m) DP DP DP DP DP DP
Present Practice Em Em Em Em Em Em
3 Hanger DP Ep/Em Ep/Em Ep/Em Ep/Em Ep/Em
Present Practice Em Ep N Ep Ep Em
4 Verandah Ep/Em Ep/Em Ep/Em Ep/Em Ep/Em Ep/Em
Present Practice Em Ep N Ep Ep N
5 Squadron Offices Ep/Em Ep/Em Opt Opt Opt Ep/Em
Present Practice N N N N N N
6 Neighboring Squadrons Dp Ep/Em Opt Opt Opt Ep/Em
Present Practice Ep N N Ep Ep Ep
7 Runway (Bird Shooter) Ep/Em Ep/Em Ep/Em Opt Not Employed
Present Practice Em Em Ep Ep N N
8 Runway (T/O End) Ep/Em Ep/Em Opt Ep/Em Ep/Em Ep/Em
Present Practice N N Ep Ep Em Em
9 GTC Post (within 50 m) Ep/Em Ep/Em Opt Ep/Em Ep/Em Ep/Em
Present Practice N N Ep Ep Em Em
10 ATC Dispersal Ep/Em Ep/Em Opt Opt Ep/Em Ep/Em
Present Practice Em Em Em Em Em Em

Discussion

The danger to hearing can be avoided by the use of appropriate type of Hearing Protection Devices (HPDs) [5, 6, 7]. HPDs presently being used by personnel working in the air stations are essentially of two types: (a) Ear Muffs and (b) Ear Plugs. National Institute of Occupational Safety and Health (NIOSH) recommends that worker shall wear hearing protectors when engaged in work that exposes them to noise that equals or exceeds 85 dBA in “8-hr TWA (LEX)” scale. Worker whose LEX (daily energy averaged sound exposure) exceed 100 dBA should wear double hearing protection (i.e. they should wear earplugs and earmuffs simultaneously) [8]. This standard can be used as a prevention strategy for protection against Occupational Hearing Loss in naval aviation. The purpose of recording the noise level (LAt) at different occupational posts during flying is to stratify the exposed personnel into different risk groups depending on their level of noise exposure.

This would help to select an appropriate HPDs for the risk groups so that they are neither under-protected nor over-protected. This study identified the occupational posts which recorded ≥ 85 dBA of noise.

A total of 93 occupational posts in 03 different air stations were surveyed for assessing the noise level and use of HPDs by the duty personnel at these posts. These occupational posts were categorized as per the level of noise and its safety standard recommended by NIOSH. As per the noise data collected from various air squadrons the occupational posts can be categorized as :-

  1. Mandatory Hearing Protection Posts, which further subdivided into:-

    Double Protection (DP) Posts

    Earplug/Earmuff(Ep/Em) Posts

  2. Optional Hearing Protection (Opt) Posts.

Of 93 occupational posts, 48 (51.6 %) posts were found to be Noise Hazardous Posts where the noise level ≥ 85 dBA. The personnel working in these posts had a mandatory requirement to use appropriate HPDs. However, the questionnaire survey conducted on duty people working at these posts to obtain the information about HPDs had shown non-complementary results. Out of these 48 posts there are 11(22.9 %) posts where duty personnel not using any kind of HPDs and 13 (27 %) posts where duty personnel were not using the appropriate HPDs. This study indicated that the compliance rate of adopting effective hearing protection is approximately 50%. The compliance rates of adopting effective noise protection were 8.3 % (aircraft dispersals), 33.3 % (hanger and open areas/verandah of squadrons), 50 % (squadron offices), 66.6 % (neighbouring squadrons, Ground Traffic Controller’s posts and Take-off end of runway) and 100 % (bird shooter’s location and ATC dispersals). Double Protection which is an effective means of protecting the worker at the aircraft dispersals or any other location where the noise level is ≥100 dBA is poorly adhered (01 against the requirement at 15 posts) to the noise safety.

The hearing conservation program practically followed in naval aviation is arguably aircrew oriented. The ground crew and other support staff who constitutes the major risk group are not effectively monitored for primordial prevention from the deleterious effects of noise. Studies have indicated that noise induced hearing loss affects 25 to 80% of ground crew depending on their length of exposure to aircraft noise [1, 9]. Lack of health awareness, improper use of HPDs, inadequate health monitoring system has made the issue more critical [10, 11]. As a result, there has been an increasing concern about the safety and health aspects of excessive exposure to noise in daily operations. 8-hour TWA (also known as LEX) using personal dosimeter is the parameter based on which the NIHL risk group can be identified. Presently, 85 dBA is considered as the safe noise exposure limit for an 8-hour time-weighted average (TWA); and for every 3 dB increase in noise level, the safe exposure time limit is cut in half. Noise dosimeter is a preferred method for worker who move around or who perform different tasks in an environment of varying noise level. However, for personnel remaining essentially stationary, recording of continuous noise levels using a sound level meter (SLM) having time integrated function is a preferred tool [12, 13]. SLM if facilitated with Octave and One-Third Octave function has the added advantage of frequency analysis. Studies have concluded that the tool which is suitable to identify the noise hazardous zone in air field/airbases is SLM and preferred parameters are LAS, LACpeak, Leq [14]. Similarly using its time integrated function the average noise level of the entire duration of exposure can be recorded. The parameter which is indicative of Leq is LAt. If the duration of exposure is known, LEX can be extrapolated by using a ‘Leq to LEX’ Normogram.

However, for noise mapping of the flying station was In this study, sound level meter was employed as a practical tool for noise mapping of various air stations. The level of noise was determined at various occupational posts by recording the Equivalent Noise Level (Leq) in a 15 min sample noise and then by using the Normogram (Leq to LEX) 8 hour TWA was obtained. By comparing the 8 hour TWA (LEX) values with existing standard (NIOSH), occupational posts could be categorized into Ear Plug/Muff (Ep/Em) post for LEX 85 to 100dBA, Double Protection (DP) post for LEX > 100dBA and Double Protection with crew rotation (DPcr) post for LEX > 115 dBA. After determining the amount of hearing protection required in a particular post, medical advice was given to use appropriate HPD in single or combination. A similar study in IAF, where analysis of on-ground and in-flight sound levels produced by Chetak and Pratap helicopters was carried out by the investigators to quantify the need for appropriate hearing protection devices [15]. This study was an attempt to carry out the noise mapping of the flying station especially various occupational posts in the technical areas by employing a SLM. There are sophisticated methods and procedures for carrying out the noise mapping of the flying stations [16,17]. However, by adhering to the good practice guides a simple device like SLM can be very effective for noise mapping [18].

Conclusions

Followings are the conclusions of this study:-

  1. 51.6 % posts were found to be Noise Hazardous posts where the noise level was more than the acceptable standard i.e. ≥ 85 dBA of LEX.

  2. There were as many as 11(22.9 %) posts where duty personnel were not using any kind of HPDs and 13 (27 %) posts where duty personnel were using the HPDs not providing adequate protection.

  3. The compliance rate of adopting effective noise protection methods were 8.3 % (aircraft dispersals), 33.3 % (hanger and open areas/verandah of squadrons), 50 % (squadron offices), 66.6 % (neighboring squadrons, Ground Traffic Controller’s posts and Take-off end of runway) and 100 % (bird shooter’s location and ATC dispersals).

  4. Double Protection which is an effective means of protecting the worker at the aircraft dispersals or any other location where the noise level is ≥100 dBA was poorly adopted (only in one post against the requirement of 15 posts).

Recommendations

Following are the recommendations:-

  1. Sound level meters should be employed as a practical tool for noise mapping of air stations.’

  2. Personnel at risk should be identified by determining the noise exposure by recording Equivalent Noise Level (Leq) in a 15 min sample noise for a particular air operation using sound level meter and interpolating LEX (8 hour TWA) by using the Leq to LEX normograph.

  3. Depending upon the level of noise in a specific occupational post, these posts can be categorized into into Ear Plug/Muff (Ep/Em) post for LEX 85 to 100dBA, Double Protection (DP) post for LEX > 100dBA and Double Protection with crew rotation (DPcr) post for LEX > 115 dBA.

References

  1. , , , . Assessment of noise environment at 28 Wing AF. Dept Project-1AMTC/23/4/89
    [Google Scholar]
  2. , . Prevalence of noise induced hearing loss in Indian Air force personnel. MJAFI. 2009;65:247-51.
    [Google Scholar]
  3. Work-Related Hearing Loss (Brochure) published by National Institute for Occupational Safety and Health Washington, DC: National Institute for Occupational Safety and Health; .
    [Google Scholar]
  4. , and . A controlled investigation of in-field attenuation performance of selected insert, earmuff, and canal cap hearing protectors. Human Factors. 1991;33:693-714.
    [Google Scholar]
  5. . State of the art: testing methods and passive hearing protectors In: , , , , , eds. Noise induced hearing loss basic mechanisms prevention and control. London: Noise Research Network Publications; . p. 187-195.
    [Google Scholar]
  6. . Methods of measuring the attenuation of hearing protection devices. J Acoust Soc Am. 1986;79:1655-87.
    [Google Scholar]
  7. , & . Double hearing protection and speech intelligibility-room for improvement. Aviat Space Environ Med. 2001;72:400-404.
    [Google Scholar]
  8. . Noise and its implication with the IAF. Journal of Aero Med Soc of India. 1973;13(1):1-11.
    [Google Scholar]
  9. . Study of noise and communication problems on the flight deck crew of an aircraft carrier: Evaluate preventive measures in use and suggest solutions. Field Project IAM, IAF 53-64.
    [Google Scholar]
  10. . Study of personal noise dosimetry on personnel exposed to aviation noise in Navy. AFMRC Project (INM, INHS Asvini). Project report No. 3731/2007
    [Google Scholar]
  11. . MIL-S8806B. . Washington,DC: US Department of Defence; [internet] 1997 Feb 12. [cited 2014 Jan 12. Availablefrom: quicksearch.dla.mil/Analyse/ImageRedirector.aspx?token=31591.36905
    [Google Scholar]
  12. , , and . Leq, SEL- What, Why & When. 8. [Internet]. [cited 2014 jan 12] Available at www.bksv.com/doc/B00051.pdf
    [Google Scholar]
  13. , . The identification and development of good practice in the field of noise mapping and the determination of associated information on the exposure of people to noise environment. EPG 1/2/4l Wolfel, Final Report. Project number p506/01
    [Google Scholar]
  14. , , . Analysis of on-ground and in-flight sound levels produced by Chetak and Pratap helicopters. Ind J of Aerospace Med. 2002;46(1):51-61.
    [Google Scholar]
  15. . Position Paper: Good Practice Guide for Strategic Noise Mapping and Production of Associated Data on Noise Exposure, Version 1 .
    [Google Scholar]
  16. . position paper: good practice guide for strategic noise mapping and production of associated data on noise exposure, version 2 .
    [Google Scholar]
  17. , . Limits and Advantages of Good Practice Guide to Noise Mapping. Paris, France: Presented at Forum Acusticum;
    [Google Scholar]
Show Sections