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Noise and hearing conservation
Korean Journal of Audiology 2011;15(2):62-66.
A Study on the Possibility of Occupational Noise-Induced Hearing Loss in Firefighters.
Min Gi Kim, Sung Jun Park, Kwan Lee, Dong Wook Lee, Kyoo Sang Kim, Hyun Sul Lim
1Department of Preventive Medicine, Dongguk University College of Medicine, Occupational Safety and Health Research Institute, Gyeongju, Korea. kwaniya@dongguk.ac.kr
2Department of Family Medicine, Dongguk University College of Medicine, Occupational Safety and Health Research Institute, Gyeongju, Korea.
3Occupational Safety and Health Agency, Research Institute, Korea Occupational Safety and Health Agency, Incheon, Korea.
Abstract
BACKGROUND AND OBJECTIVES
Firefighters face serious risks to their health and safety in the performance of their duties. In addition to the diverse occupational hazards well-known to the public, firefighters are also occasionally exposed to high levels of noise, such as sirens, horns, and electronic alerting signals.
MATERIALS AND METHODS
We first measured the noise emitted by two fire trucks and one ambulance. Next, we enrolled 171 firefighters (164 males, seven females). We designated the employees of a private school as controls for the firefighter group. After selecting workers, including audiometric testing at 1,000 and 4,000 Hz, the groups were age- and gender-matched. Both groups were included separately for the right and left ears at pure-tone test frequencies at 1,000 and 4,000 Hz. We chose the better ear thresholds and analyzed the differences in hearing levels at each frequency and each age group between the firefighters and controls.
RESULTS
The sound pressure levels of the siren in and out of an ambulance, the first fire truck, and the second fire truck were 99.3 dB (A) and 108.9 dB (A), 92.3 dB (A) and 108.3, and 78.8 dB (A) and 99.0 dB (A), respectively. At 4,000 Hz, the hearing threshold was significantly increased by work period (p<0.01). Each hearing threshold level was significantly higher than controls (p<0.01).
CONCLUSIONS
Many of the noise sources produce sounds exceeding 90 dB (A), and some firefighters may be exposed for brief periods to levels that exceed 105-110 dB (A). The hearing threshold level in firefighters is higher than the general population and noise-induced hearing loss in firefighters is possible. In the future, consistent, effective, and long-standing implementation of hearing conservation programs are needed, and special health examinations for hearing levels in firefighters must be conducted.
Keywords: Firefighter;Hearing loss;Occupational noise

Address for correspondence : Kwan Lee, MD, Department of Preventive Medicine, Dongguk University College of Medicine, 87 Dongdae-ro, Gyeongju 780-350, Korea
Tel : +82-54-770-8291, Fax : +82-54-770-8290, E-mail : kwaniya@dongguk.ac.kr

Introduction


Firefighting is a very dangerous profession, which includes health threats due to inhalation of heat-generated by-products, ash, mental stress, and the ergonomic consequences of inappropriate posture. Firefighting has been linked to the increased risks of respiratory and cardiovascular diseases, reproductive system disorders, musculoskeletal diseases, physical injury, and cancer.1) Furthermore, firefighters can be exposed to loud noise. A survey of 230 firefighters in the United States reported that over 90% replied that the good hearing is essential to the firefighter's business.2)
Noise, which is considered to be unwanted sound, has emerged as a serious health problem in industrialized societies.3,4) Occupational hearing loss in the workplace typically involves sensorineural hearing loss in both ears, which is caused by exposure to high frequency sound, and which shows the characteristics of a dose-response relationship. However, occupational hearing loss is variously affected by the character of the noise; sound pressure level noise exposure period, time, or environment; and personal susceptibility.5)
Firefighters are routinely exposed noises such as sirens, horns, alarms, fire engine sounds, and traffic. This noise mostly exceeds 90 dB (A) and can attain harmful short-term levels of 105-110 dB (A).2) Studies on the consequences of noise exposure in firefighters have been conducted,2,6,7,8,9,10,11,12) but not in Korea. The present study was undertaken to address this shortcoming, with the aim of providing data that will be useful in promoting the health of Korean firefighters. 

Materials and Methods

Subjects
The subjects of this study were 171 firefighters at a local fire station, Gyeongsangbuk-do. The controls were not firefighters (university personnel) who were matched in terms of gender and age (±5 years). 

Methods 

Measurement of noise exposure
Workplace noise measurement was conducted based on Korea Ministry of Labor regulations. The personal and environmental exposure measurements were done simultaneously, including personal exposure measurements taken inside of two fire trucks and one ambulance. Personal measurements were recorded using a Noise Dosimeter Q100 device (Quest Technologies, Oconomowoc, WI, USA) worn by each subject on the collar within 30 cm of the auricle. Measurements involved a time weighted average (TWA). The measuring equipment setup consisted of an exchange rate of 5 dB (A), threshold level of 80 dB (A), and criterion level of 90 dB (A). The measurements in the vehicle interiors were taken with the window open, reflecting the real-life condition. The vehicle measurement sites on the interior, exterior, and roof of the ambulance and the interior and exterior of the fire trucks were selected to expose the firefighters directly to the source of the noise. Three sound level frequency measurements were acquired using a Sound Level Meter 2900 (Quest Technologies) and cumulative noise exposure was measured using a Noise Dosimeter Q100 (Quest Technologies). The measured values were averaged arithmetically. The external measurements were performed 1 m from the front side of vehicle, with the microphone being fixed in place with a 10 cm separation between it and the roof of the vehicle. 

Hearing test
The threshold of air conduction as hearing loss was measured at a frequency of 1,000 Hz and 4,000 Hz for the firefighter and control groups. The hearing test was conducted in an audiometry booth by a nurse certified in hearing quality control by the Korea Occupational Safety and Health Agency using a model GSI 16 audiometer (Grason-Stadler, Eden Prairie, MN, USA). After summing the threshold of both ears at 1,000 Hz and 4,000 Hz, the superior ear was identified. When both ears were equal, the good ear was selected based on the response at 4,000 Hz.2) Through this, the hearing threshold of the selected ear was done with the hearing threshold of the subject. 

Statistical analyses
At frequencies of 1,000 Hz and 4,000 Hz, the difference of the hearing threshold by the working period was analyzed using one-way analysis of variance. The difference of the hearing threshold between firefighters and controls by age for both frequencies was analyzed by the paired t-test. A p value<0.05 was determined as significant. 

Results

General characteristics
The 171 firefighters comprised 164 males (95.9%) and seven females (4.1%). Seventy-six firefighters (44.4%) were 31- 39-years-of-age and 55 (32.2%) were 41-49-years-of-age. Seventy-nine of the firefighters (42.2%) had <5 years of experience, and 43 people (25.1%) had ≥5 years or <10 years of experience. In the control group, 80 people (46.8%) and 53 people (31.0%) were 31-39-years-of-age 41-49-years-of-age, respectively (Table 1).

Sound pressure levels of vehicles
The sound pressure level measurements from the interior and exterior of the ambulance were 99.3 dB (A) and 108.9 dB (A), respectively. The sound pressure level in the interior and exterior, and roof, of one fire truck was 92.3 dB (A), 108.3 dB (A), and 100.0 dB (A), respectively. The measurements in the same respective order from the second fire truck were 78.8 dB (A), 99.0 dB (A), and 107.3 dB (A)(Table 2).

Comparison of hearing threshold between firefighters and controls
The hearing threshold of firefighters at frequencies of 1,000 Hz and 4,000 Hz displayed a temporal increase. This temporal increase was more significantly pronounced at 4,000 Hz (p<0.01)(Table 3). The hearing threshold between firefighters and controls by age group was not different at ages 41-49 years and <30-years-of-age, but was significantly higher in controls aged 31-39 years and >50-years-of-age (Table 4).

Discussion

The siren of the fire truck needs to be greatly amplified to alert personnel and passersby to the presence and movement of the vehicle. The associated sound pressure level can be 120 dB (A) or more.4) Firefighters have complained of hearing loss they attributed to the siren noise, to the extent that a group of firefighters in the United States lodged a lawsuit with the siren manufacture company seeking compensation.13) In Korean, the regulations pertaining to motor vehicle safety standards mandate that the sound pressure level of siren must exceed 90 dB (A) but not surpass 120 dB (A) at a point 30 m in front of the vehicle.14) 
In this study, the sound pressure level of the ambulance and fire trucks was 78.8-99.3 dB (A), lower than the range of 103.4-114.5 dB (A) recorded in U.S studies of firefighters.7,8,9,10,11,12) However, it is possible that the type of vehicle (i.e., ambulance or fire truck) and firefighter's location in/on the vehicle affects an individual's noise exposure differently. Consistent with this view, the present measurements differed between the fire trucks. The soundproofing nature of vehicles can affect noise exposure, as can the location of the siren (i.e., driver's side or passenger side). There was little difference in external noise levels, including the roofs of the fire trucks, suggesting that the exterior noise is not as subject to variation. However, exposure to 120-150 dB (A) is possible if it is assumed that the siren is mostly positioned within 1 m of firefighters when they dispatched to the field.14) It is likely that a firefighter typically will not exceed the 8-h TWA noise intensity of 90 dB (A), since the transit time from station to the incident site is usually <30 min. However, when Korean motor vehicle safety standards are considered, firefighters likely exceed the noise standards pertaining to exposure to noise levels exceeding 115 dB (A) generated 15 min in one day.8,15) Generally, firefighters' noise exposure is more intense and for a shorter time than individuals in manufacturing environments.4)
In the U.S., the National Institute for Occupational Safety and Health (NIOSH) has conducted several large-scale studies of noise exposure of firefighters.9,10,11,16,17) These studies was conducted in New York State,16) New York City,17) Memphis,9) Pittsburgh,10) and Hamilton.11) In these studies, the total noise exposure level of the firefighters exceeded 120 dB (A) instantaneously during short-term periods such as the scramble to prepare for fire station departure, but did not exceed the 8-h thresholds of 90 dB (A) mandated by the Occupational Safety and Health Administration (OSHA) and 85 dB (A) mandated by NIOSH. Yet, even though the noise exposure levels of most fire fighters did not exceed the OSHA or NIOSH standards, hearing loss occurs. It may be that it is not the intensity or duration of sound exposure, but rather the frequency of the noise that is influential in hearing loss. In this respect, noise-related hearing loss is an occupational hazard of fire fighting. 
According to data of the A Los Angeles-based study conducted by the National Emergency Management Agency compared the hearing loss in 750 firefighters with age-matched individuals from the general population. The incidence rate of hearing loss in firefighters was very high, and a correlation with the exposure to siren noise was revealed.8) Also, the incidence rate of hearing loss about 192 firefighters in Houston, Texas was very high.7) According to a 1991 NIOSH study, 170 of 333 firefighters (51.1%) showed hearing loss in one or both ears.9) A 1995 NIOSH study documented a hearing loss rate of about 90% in firefighters due to exposure to excessive noise. In the latter study, hearing loss progressively increased with increasing frequency of noise between 3,000 Hz and 6,000 Hz, and over time.11) A study involving 340 firefighters in the state of Massachusetts and matched individuals from the general population documented lower hearing thresholds in the firefighters between 3,000 Hz and 6,000 Hz, but higher hearing threshold in older firefighters compared to controls.18) However, the significance of the latter observations is unclear, since the older individuals were also more apt to experience exposure to other detrimental and confounding sources of noise, including lawnmowers, music (particularly heavy metal), and noise incurred in the course of a second job. But, when firefighters who had participated in a long-term hearing conservation program were compared with the general population, there was no difference of hearing threshold in 3,000 Hz and 6,000 Hz.18) These collective results supported the idea that hearing loss in firefighters can occur due to noise encountered during their fire fighting duties.2)
Noise-induced hearing loss is frequently observed in the general population, and is especially common in older individuals and the elderly. Therefore, in this study, we used gender- and age-matched office workers as the control.2) However, because military service career and health history of the subject were aspects of the C1 grade received by firefighters during periodic occupational health examinations, the change of the hearing threshold in this study cannot help but be limited. Therefore, in order to resolve these problems, we adopted the hearing threshold of the good ear.
Presently, the firefighters were exposed to short-term noise that exceeded 90 dB (A), and the hearing threshold in 1,000 Hz as well as 4,000 Hz was significantly different by working period. Also, hearing threshold increased with age compared with the control group. These observations echo those from previous studies, and suggest that noise-induced hearing loss occurs in Korean firefighters in the course of the active firefighting duty. The influences of other facets of the job, including emergency rescue, warrants further study. 
The present results highlight the importance of hearing loss education for incoming firefighters. As well, all firefighters should be provided with noise-muffling ear ware. Noise protection equipment must be easy to wear, effective, and, because of its probable flammability, easy to remove at the fire scene. Also, since communication at a fire scene often involves the use of an earpiece and microphone, the noise abatement equipment needs to be removed for safety reasons. Wearing noise muffling equipment should be mandatory.6) OSHA has operated a hearing conservation program for firefighters, which has proven to be effective. Also, the American National Fire Protection Association (NFPA) has legislated and operates standards and regulations for the safety and health of firefighters.20) NFPA 1500 legislated a standard for a firefighter occupational safety and health program of the firefighters was legislated, and NFPA 1582 established an integrated medical program for firefighters. However, measurement for the noise and medical examination in Korea is still not legally required. Since 2006, the Korean National Emergency Management Agency has conducted special noise-related medical examinations. With time, the accumulating data should prove to be a valuable resource in studies of noise-induced hearing loss in Korean firefighters. 
In addition to such studies, a hearing conservation program and the modification of the rules on motor vehicle safety standards may be prudent steps. The present study represents the beginning of this process. Our data calls attention to the important issue of health problems related to firefighting duty in the firefighters, specifically noise-induced hearing loss. 
A limitation of this study was the inability to measure the sound pressure level for each frequency in the vehicles. And, we were unable to measure noises such as the background noises at the fire site (e.g., water hoses). Further studies should incorporate measurement of background noise. In addition, although the technology of noise reduction is greatly improved, there are no data about the noise exposure for Korean firefighters. In the case of foreign data, it is difficult to reflect the current level, as the data was often collected decades ago. 


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  13. Roylance FD. Firefighters sue siren manufacturer over hearing loss. [cited 2010 August 27]. Available from: URL:http://www.4hearin-gloss.com/archives/2005/12/firefighters_su.html.

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