Personal Noise Exposure Assessment and Noise Level Prediction Through Worst-Case Scenarios for Korean Firefighters

Abstract

Firefighters experience high noise levels from various sources, such as sirens, alarms, pumps, and emergency vehicles. Unlike industrial workers who experience continuous noise exposure, firefighters are subject to intermittent high-intensity noise, increasing their risk of noise-induced hearing loss (NIHL). Despite global concerns regarding firefighters’ auditory health, research on Korean firefighters remains limited. This study aimed to assess personal noise exposure among Korean firefighters across three primary job roles—fire suppression, rescue, and emergency medical services (EMS)—and to predict worst-case noise exposure scenarios. This study included 115 firefighters from three fire stations (one urban, two suburban). We measured personal noise exposure using dosimeters attached near the ear following the Korean Ministry of Employment and Labor (MOEL) and International Organization for Standardization (ISO) criteria. Measurements included threshold levels of 80 dBA, exchange rates of 5 dB (MOEL) and 3 dB (ISO), and a peak noise criterion of 140 dBC. We categorized firefighters’ activities into routine tasks (shift handovers, equipment checks, training) and emergency responses (fire suppression, rescues, EMS calls). We performed statistical analyses to compare noise levels across job roles, vehicle types, and specific tasks. The worst-case exposure scenarios were estimated using 10th percentile recorded noise levels. The average 8 h time-weighted noise exposure levels varied significantly by job role. Rescue personnel exhibited the highest mean noise exposure (MOEL: 71.4 dBA, ISO: 81.2 dBA; p < 0.05), whereas fire suppression (MOEL: 66.5 dBA, ISO: 74.2 dBA) and EMS personnel (MOEL: 68.6 dBA, ISO: 73.0 dBA) showed no significant difference. Peak noise levels exceeding 140 dBC were most frequently observed in rescue operations (33.3%), followed by fire suppression (30.2%) and EMS (27.2%). Among vehicles, noise exposure was the highest for rescue truck occupants. Additionally, EMS personnel inside ambulances had significantly higher noise levels than drivers (p < 0.05). Certain tasks, including shift handovers, equipment checks, and firefighter training, recorded noise levels exceeding 100 dBA. Worst-case scenario predictions indicated that some work conditions could lead to 8 h average exposures surpassing MOEL (91.4 dBA) and ISO (98.7 dBA) limits. In this study, Korean firefighters exhibited relatively low average noise levels. However, when analyzing specific tasks, exposure was sufficiently high enough to cause hearing loss. Despite NIHL risks, firefighters rarely used hearing protection, particularly during routine tasks. This emphasizes the urgent need for hearing conservation programs, including mandatory hearing protection during high-noise activities, noise exposure education, and the adoption of communication-friendly protective devices. Future research should explore long-term auditory health outcomes and assess the effectiveness of noise control measures.

1. Introduction

For firefighters, hearing is not an option but a necessity. Firefighters’ hearing levels are critical, as they perform complex and varied emergency tasks while communicating via radio during their operations [1]. Firefighters are occupationally classified as a high-risk noise exposure group [2,3,4] and are also exposed to various hazards [5,6,7,8,9,10,11,12,13,14]. Noise-induced hearing loss (NIHL) is permanent, and once hearing is lost, it cannot be recovered [15]. Firefighters experience intermittent high-intensity noise exposure rather than the continuous noise exposure typical of industrial workers [3]. According to the literature, firefighters are exposed to various sources of noise, including sirens, alarms, firefighting pumps, rescue equipment (chainsaws, pneumatic chisels, etc.), ventilation fans, vehicle engines, and radios [1,3,16].

Many studies have shown that firefighters are exposed to varying levels of occupational noise depending on their specific tasks and roles, with average exposure ranging from 65 to 88 dBA and occasional peaks exceeding 140 dBC [1,3,4,17,18,19,20,21,22,23]. While some studies reported levels below 85 dBA [19,20,21], others noted that short-duration, high-intensity noise—such as that from sirens and rescue equipment—frequently exceeded permissible limits and was linked to hearing loss, particularly in the high-frequency range of 3–6 kHz [2,16,22,24,25,26,27,28,29,30,31,32]. Multiple studies have identified a correlation between noise exposure and years of service, with older firefighters showing greater hearing loss, though early-stage auditory damage has also been reported among younger personnel [18,31,32]. Despite such global evidence, limited research has focused on the specific patterns and risks of noise exposure among Korean firefighters, necessitating further investigation.

As of 2023, there were 67,358 firefighters in Korea across 235 local fire departments, with each firefighter responsible for approximately 780 people [33]. Among these, the number of specialized rescue personnel was 5432, and emergency medical service (EMS) personnel numbered 13,896, with both roles increasing annually. Volunteer firefighters numbered 95,208, bringing the total number of firefighters in Korea to 162,566, of which 59% were volunteer firefighters and 41% were career firefighters. According to the National Fire Protection Association [34], the U.S. has 1,100,000 firefighters, with 27% career firefighters and 73% volunteers, indicating a higher proportion of career firefighters in Korea than in the U.S. In 2022, the number of responses (fire, rescue, and EMS) totaled 12,546,469, with EMS calls accounting for the largest proportion (61%). The primary duty of firefighters in fire suppression roles involves extinguishing fires, categorized by locations such as residential buildings, non-residential buildings, vehicles, rail vehicles, hazardous gas manufacturing plants, ships, aircrafts, and wildland fires. Among these, non-residential fires accounted for the highest proportion (37%) in 2022 [33]. The types of rescue incidents are diverse, including fire, traffic accidents, elevator entrapments, confined persons, suspected suicides, location checks, mountain rescues, water rescues, entrapments, collapses, crush injuries, leaks, explosions, terrorism suspicions, aircraft incidents, beehive removals, animal handling, and lock openings. EMS personnel perform the most frequent dispatches, providing emergency medical care and patient transport.

Although official data on Noise-Induced Hearing Loss (NIHL) among Korean firefighters are unavailable, trends among Korean construction workers have shown a continuous increase [35]. Occupational hearing protection is highly important in the United States, highlighted by its inclusion in the 2010 National Institute for Occupational Safety and Health (NIOSH) agenda, which aims to reduce hearing loss among workers [3]. However, data on noise exposure assessments for Korean firefighters remain limited. Kang [19] evaluated noise exposure by task (rescuers, drivers, and commanders), reporting average noise levels of 84.6 dBA for rescuers, 83.3 dBA for vehicle drivers, and 79.5 dBA for commanders. Chung et al. [17] compared hearing test results of Korean factory workers and firefighters. This study highlights the insufficiency of noise exposure data for firefighters. Lee et al. [23] conducted a continuous six-day noise evaluation on five firefighters, reporting an average noise level of 65.3 dBA based on MOEL criteria and a notably high average noise level of 111.9 dBA during dispatches. Kang et al. [36] performed a 24 h noise exposure evaluation with seven firefighters. Studies on task-specific personal noise exposure conducted thus far have reported limitations in generalizing firefighters’ noise levels owing to small sample sizes. Therefore, we assessed personal noise exposure among 115 Korean firefighters by job role (fire suppression, EMS, and rescue) and specific task, and to predict noise exposure levels by constructing worst-case scenarios using task-specific noise levels.

2. Materials and Methods

2.1. Study Subjects

We contacted 235 fire stations with an official letter to recruit participating sites. Three stations agreed to participate in this study. One (Station A) was located in an urban area and two (Stations B and C) were located in suburban areas. Participants at each fire station were firefighters engaged in fire suppression, rescue, and EMS job roles, with administrative employees who primarily worked in offices serving as the control group. A total of 123 firefighters participated in the personal noise exposure assessment; however, 115 firefighters remained after excluding participants due to noise data errors or absence (e.g., leave). The evaluated vehicles included command and pump vehicles for fire suppression roles, rescue vehicles for rescue roles, and ambulances for EMS roles, with both drivers and onboard personnel assessed. As this study involved human subjects, it was conducted after receiving IRB approval (OSHRI-202402-HR-006) from the Occupational Safety and Health Research Institute.

Korean firefighters operate on a three-shift rotation schedule, working 24 h followed by two days off. We conducted measurements consecutively for three days to assess all three shifts, and for personal noise assessments. We attached dosimeters near the ear on the firefighter’s right or left shoulder. We used noise dosimeters included the Casella Model CEL-35x dBadge (Casella, Bedford, UK), TSI Model EG4P-NB dosimeter (TSI, Shoreview, MN, USA), and Svantek Model 104IS (Svantek, Warsaw, Poland). We calibrated the dosimeters before and after the measurements using a sound calibrator generating a 1 kHz pure tone at 114 dB. The sound calibrators were certified by the Korea Laboratory Accreditation Scheme (KOLAS), an officially accredited institution in South Korea.

To classify firefighter tasks, firefighters participating in the noise measurements recorded their daily activities and subjectively reported noise characteristics. Owing to the nature of firefighting work involving frequent emergency situations, it was challenging for participants to remember every detail. Thus, the precise classification of tasks was supported by accessing each firefighter’s recording system to obtain accurate dispatch times, return times, number of dispatches, and brief descriptions of the tasks performed (Figure 1).

2.2. Personal Noise Exposure Assessment

We set the noise dosimeters according to the Korean Ministry of Employment and Labor (MOEL) and ISO criteria. The MOEL criteria included A-frequency weighting, a slow time response, a criterion level of 90 dBA, an exchange rate (ER) of 5 dB, and an 80 dBA threshold. ISO criteria included A-frequency weighting, a slow time response, an 85 dBA criterion level, a 3 dB exchange rate (ER), and an 80 dBA threshold. Additionally, peak noise levels were measured in dBC to determine the frequency and proportion exceeding the recommended peak noise limit of 140 dBC [37]. A- and C-frequency weightings are standardized frequency filters used in noise measurements. A-weighting simulates human hearing sensitivity at moderate levels by reducing low and high frequencies, and is commonly used in environmental and occupational noise assessments. C-weighting provides a flatter response, making it more appropriate for measuring high or peck noise levels. Although firefighters work 24 h shifts, we converted noise levels to an 8 h exposure standard (MOEL: 90 dBA, ISO: 85 dBA) for comparison, calculated using Equation (1) below. We compared the converted noise levels with job roles, vehicle types, and tasks against both MOEL and ISO exposure standards, and the number and proportion of samples exceeding these standards were analyzed.

$${\mathrm{L}}_{\mathrm{e}\mathrm{q},\mathrm{d}}={\mathrm{L}}_{\mathrm{e}\mathrm{q},{\mathrm{T}}_{\mathrm{e}}}+(\mathrm{q})\mathrm{l}\mathrm{o}\mathrm{g}({\displaystyle \frac{{\mathrm{T}}_{\mathrm{e}}}{{\mathrm{T}}_{\mathrm{o}}}})$$

(1)

where L_eq,d (dBA) is the 24 h noise exposure level adjusted to an 8 h standard, L_eq,Te (dBA) is the noise level during the exposure period, T₀ is 8 h, and T_e is the exposure duration. The value ’q’ is calculated as ‘ER/log2’, yielding 16.61 for the MOEL method (ER = 5 dB) and 10 for the ISO method (ER = 3 dB).

Equation (2) was used to compare task-specific noise levels. We classified tasks based on firefighters’ activity logs and the station’s recording system data. Noise values were calculated separately according to the Korean MOEL (L_AVE) and ISO (L_eq) standards. We used the 10th percentile recorded noise values for each task to predict the noise exposure through worst-case scenarios by applying task-specific time weighting.

$${\mathrm{L}}_{\mathrm{e}\mathrm{q}},{\mathrm{a}\mathrm{c}\mathrm{t}}_{\mathrm{i}\mathrm{j}}=(\mathrm{q}){\mathrm{l}\mathrm{o}\mathrm{g}}_{10}{\displaystyle \frac{1}{{\mathrm{n}}_{\mathrm{i}\mathrm{j}}}}{\sum }_{\mathrm{k}=1}^{\mathrm{N}}{10}^{{\displaystyle \frac{{\mathrm{L}}_{{\mathrm{e}\mathrm{q}}_{\mathrm{i}\mathrm{j}\mathrm{k}}}}{(\mathrm{q})}}}$$

(2)

where n_ij represents the duration of performing task j at fire station i, and L_eq, act_ij (dBA) is the noise level generated during task j at station i over time (k). The value ‘q’ is calculated as ‘ER/log2’, yielding 16.61 for the MOEL standard (ER = 5 dB) and 10 for the ISO standard (ER = 3 dB).

2.3. Data Analysis

We performed statistical analyses using the SPSS 29.0 statistical package (IBM Corp, NY, USA) to compare the converted 8 h time-weighted average noise levels (MOEL and ISO) by job role, vehicle type, and task using an analysis of variance (ANOVA). We also conducted Tukey’s post hoc test to identify statistical differences between the groups. To compare L_eq, act_ij among tasks, ANOVA was performed, followed by Tukey’s post hoc test to examine statistical differences between groups. We visualized and analyzed box plots using Sigma Plot 14.0 software (Systat Software Inc., San Jose, CA, USA).

3. Results

The number of firefighters at fire stations A, B, and C were 38, 40, and 37, respectively. By job role, there were 43 firefighters in fire suppression: 8 command vehicle drivers, 8 commanders, 9 pump vehicle drivers, and 18 firefighters. There were 27 firefighters in rescue roles: 9 rescue vehicle drivers and 18 rescue personnel. EMS roles included 22 firefighters, 9 ambulance drivers and 13 EMS personnel, and there were 23 administrative employees (

Table 1. Number of participants included in personal noise assessments across three fire stations.

Job	Vehicle	Task	Station			Subtotal	Total
			A	B	C
Fire Suppression	Command vehicle	Driver	2	3	3	8	16	43
		Commander	3	2	3	8
	Pump vehicle	Driver	3	3	3	9	27
		Firefighter	6	6	6	18
Rescue	Rescue vehicle	Driver	3	3	3	9	27
		Rescue personnel	6	6	6	18
EMS	EMS Ambulance	Driver	3	3	3	9	22
		EMS personnel	4	6	3	13
Administrative *	-	Administrative staff	8	8	7 *	23	23
Subtotal			38	40	37
Total			115

* Control group.

).

The tasks of 115 firefighters were classified using individual activity logs and fire station recording systems. Common tasks included shift handovers, equipment checks, training, and other duties. Each job role included dispatches and training tasks. During the measurement period, fire suppression dispatches included fence fires, air conditioner outdoor-unit fires, indoor gas stove fires, balcony fires, and false alarms, and training involved building collapse fire scenarios, air mattress response drills, high-rise fire tactics, and fire hydrant occupation drills. Rescue tasks included dispatches for traffic accidents, animal capture, lock opening, welfare checks, and wasp nest removal, and involved training on double-ladder operations and rope knot techniques. EMS tasks predominantly involved patient transfers to hospitals or returns after on-site treatment, and training included setting up temporary medical stations during fires and on-site emergency medical tactics. Administrative staff were primarily stationed in offices performing administrative duties (

Table 2. Task description.

Task	Description
Common (excluding administrative)	▪ Shift handover (duty transfer and task briefing) ▪ Equipment checks (vehicle sirens, radios, horns, rescue equipment, firefighting gear inspection) ▪ Education (safety training, drunk driving prevention) ▪ Other duties (physical fitness training, etc.)
Fire Suppression	▪ Dispatches * (fence fires, air conditioner unit fires, indoor stove fires, balcony fires, detector malfunctions, etc.) ▪ Training (building-collapse fire drills, air mattress deployment drills, high-rise firefighting tactics, hydrant occupation drills, etc.)
Rescue	▪ Dispatches * (traffic accidents, animal capture, door unlocking, welfare checks, wasp nest removal, etc.) ▪ Training (ladder manipulation drills, rope knot training, etc.)
EMS	▪ Dispatches * (hospital transfers, return after on-site treatment, etc.) ▪ Training (temporary emergency medical post installation drills during fires, on-site emergency medical tactics training, etc.)
Administrative	▪ Primarily stationed in offices performing administrative tasks (scheduling shifts, procuring equipment, maintaining records, etc.)

* Dispatch descriptions were based on actual activities performed on the measurement day.

).

Eight-hour time-weighted average noise levels were compared across each job role based on the MOEL and ISO criteria. Rescue roles showed significantly higher noise levels (p < 0.05), with average levels of 71.4 dBA (MOEL) and 81.2 dBA (ISO). No statistically significant differences were observed between fire suppression and EMS roles; EMS roles had average noise levels of 68.6 dBA (MOEL) and 73.0 dBA (ISO), and fire suppression roles had average levels of 66.5 dBA (MOEL) and 74.2 dBA (ISO). The proportion exceeding the peak noise criterion of 140 dBC was highest for rescue roles at 33.3% (9 cases), followed by fire suppression (30.2%, 13 cases) and EMS (27.2%, 6 cases). The number of emergency responses was lowest for rescue roles (43 cases) and highest for EMS roles (73 cases). Despite having the lowest frequency of responses, rescue roles had the highest average noise levels and the highest proportion exceeding the 140 dBC peak noise criterion. When comparing the average noise exposure between vehicles, firefighters onboard rescue vehicles exhibited significantly higher noise levels (p < 0.05) (

Table 3. Comparison of adjusted 8 h time-weighted average noise levels, Leq,d (dBA), and peck noise levels (dBC) by type of job, vehicle, and calls (MOEL/ISO).

Job **	Vehicle ***	N	MOEL(Leq,d) *		ISO(Leq,d) *		N > 140 dBC (%)	Calls (Calls by Shift)
			Mean (SD)	95% CI	Mean (SD)	95% CI
Fire suppression B ****	Command vehicle B	16	62.5 (8.4)	58.0, 67.0	74.5 (7.3)	70.6, 78.4	3 (18.8)	18 (2.0)
	Pump vehicle B	27	68.9 (4.0)	67.3, 70.4	76.6 (3.3)	75.3, 77.9	10 (37.1)	51 (5.7)
Rescue A	Rescue vehicle A	27	71.4 (5.6)	69.2, 73.7	81.2 (7.4)	78.3, 84.1	9 (33.3)	43 (4.8)
EMS B	Ambulance B	22	68.6 (6.7)	65.7, 71.6	76.5 (5.8)	73.9, 79.1	6 (27.2)	73 (8.1)
Administrative C	-	23	49.1 (8.9)	45.2, 52.9	63.6 (6.0)	61.0, 66.2	0	-

* p-value < 0.05, ** ANOVA and Tukey’s post hoc analysis (Tukey B) were performed between job groups, *** ANOVA and Tukey’s post hoc analysis (Tukey B) were performed between vehicle groups. **** ^A–C indicate significant differences based on Tukey post hoc test results.

, Figure 2 and Figure 3).

The average noise levels between vehicle drivers and onboard firefighters were compared for each vehicle type. Ambulance onboard personnel exhibited significantly higher average noise levels of 70.6 dBA (MOEL criteria) compared to ambulance drivers, who had an average of 65.8 dBA (p < 0.05). However, no statistically significant differences in average noise levels were found between drivers and onboard firefighters in other job roles. Vehicle drivers had a higher proportion of peak noise levels exceeding 140 dBC than onboard firefighters. According to the MOEL criteria, only 3 cases exceeded 80 dBA; however, 25 cases exceeded 80 dBA according to the ISO criteria. While none of the cases exceeded 85 dBA based on the MOEL criteria, 11 cases exceeded this level according to the ISO criteria, and 4 cases exceeded 90 dBA. The administrative staff did not record any instances exceeding the 140 dBC peak noise criterion (

Table 4. Comparison of mean (max) noise level (dBA) by exchange rate (5 dB ER, 3 dB ER) and peak noise level (dBC) by job title.

Job Title	Vehicle	Categories	N	Mean(Max) (dBA)		N > 80 dBA		N > 85 dBA		N > 90 dBA		N > 140 dBC (%)
				LMOEL *	LISO *	LMOEL	LISO	LMOEL	LISO	LMOEL	LISO
Fire Suppression	Command vehicle	Driver B	8	59.9 (72.0)	72.0 (79.8)	0	0					2 (25.0)
		Commander B	8	65.1 (80.7)	76.5 (88.5)	0	3		2		0	1 (12.5)
	Pump vehicle	Driver A	9	69.5 (73.1)	78.9 (83.1)	0	3		0			8 (88.9)
		Personnel A	18	68.5 (74.2)	75.5 (82.2)	0	2		0			2 (11.1)
Rescue	Rescue vehicle	Driver A	9	81.7 (80.1)	81.8 (98.5)	1	5	0	2		1	6 (66.7)
		Personnel A	18	71.3 (80.6)	80.8 (98.6)	1	9	0	4		2	3 (16.7)
EMS	EMS Ambulance	Driver B	9	65.8 (76.7)	76.9 (88.4)	0	2		2		0	4 (44.4)
		Personnel A	13	70.6 (81.6)	76.2 (91.0)	1	1	0	1		1	2 (15.4)
Administrative	-	Administrative staff C	23	49.1 (66.5)	63.6 (74.9)	0	0					0
Total (%)			115			3 (3)	25 (22)	0	11 (10)	0	4 (3)

* p-value < 0.05; ^A–C indicate significant differences based on Tukey post hoc tests (L_MOEL values).

and Figure 4).

Tasks were classified for 92 firefighters, excluding administrative staff. The tasks were categorized into emergency responses (fire suppression, rescue, and EMS), shift handovers, equipment checks, firefighter training, firefighter education, other duties, and standby at the station. The average durations for each task over the 24 h period were analyzed and compared. Emergency responses had an average duration of 192 min (13.3%), shift handovers and equipment checks had the shortest average durations of 17 min (1.2%) and 56 min (3.9%), respectively, and standby at the station had the longest average duration of 952 min (66.1%). Average noise levels (MOEL criteria) ranged from 51.7 to 69.6 dBA; firefighter training showed the highest maximum value at 94.3 dBA, followed by equipment checks at 93.8 dBA, shift handovers at 92.2 dBA, and emergency responses at 86.5 dBA. Under the ISO criteria, maximum noise levels exceeded 100 dBA during shift handovers (100.5 dBA) and equipment checks (107.6 dBA), whereas firefighter training (96.5 dBA) and emergency responses (94.2 dBA) exceeded 90 dBA. Standby at the station had the highest proportion (46.4%) of instances exceeding 140 dBC when the tasks were analyzed individually. Overall, 66.1% of the instances exceeding 140 dBC occurred during in-station tasks, including standby at the station (

Table 5. Comparison of time, mean, X₉₀ noise level (dBA) by MOEL/ISO, and peak noise level (dBC) by type of task.

		Time (min)		MOEL *		ISO *		N > 140 dBC (%)
Task Type	N	Mean (SD)	% of 24 h	Mean (SD)	X10 *	Mean (SD)	X10
Emergency response B **	86	192 (141)	13.3	66.7 (8.3)	74.6	74.6 (6.4)	80.6	11 (19.6)
Shift handover B	41	17 (8)	1.2	66.7 (12.9)	82.9	75.1 (11.2)	91.0	0
Equipment checks A	80	56 (43)	3.9	69.6 (9.5)	80.7	77.5 (9.0)	88.5	6 (10.7)
Firefighter training B	47	176 (124)	12.2	61.6 (12.0)	75.0	71.6 (8.7)	82.7	8 (14.3)
Firefighter education C	67	165 (92)	11.5	53.1 (13.7)	68.0	65.1 (9.6)	76.3	4 (7.1)
Other duties C	29	84 (34)	5.8	51.7 (14.8)	68.9	64.2 (9.6)	75.3	1 (1.8)
Standby at the station C	92	952 (174)	66.1	52.7 (7.8)	62.1	66.8 (5.9)	74.3	26 (46.4)

* The value was for 10th percentile noise levels. ** ^{A, B, C} indicate significant differences based on Tukey post hoc tests

).

Using the 10th percentile noise levels from Table 5, noise exposure was estimated by creating worst-case scenarios. Scenario 1 was calculated using the task durations and 10th percentile noise values from Table 5. The resulting 8 h time-weighted average noise levels of all scenarios did not exceed the threshold exposure limit value of noise. The resulting 8 h time-weighted average noise levels of scenario 1 were, respectively, 77.9 dBA (MOEL) and 84.7 dBA (ISO). Scenario 2 considered 4 h of firefighter training and 20 h of standby at the station, resulting in 74.4 dBA (MOEL) and 82.1 dBA (ISO). Scenario 3 involved 30 min each of shift handover and equipment checks, 10 h of emergency response, and 14 h of standby at the station, yielding noise levels of 79.1 dBA (MOEL) and 84.9 dBA (ISO). Scenario 4 involved 30 min each for shift handover, equipment checks, emergency response, and other duties, and 22 h of standby at the station, resulting in 79.1 dBA (MOEL) and 84.9 dBA (ISO) (

Table 6. Worst-case scenario for performing firefighters’ tasks during a 24 h shift.

No.	Scenario (h) *	LMOEL,24h	LMOEL,8h	LISO,24h	LISO,8h
1	Shift handover (0.5), Equipment checks (0.5), Firefighter training (3), Education (2), Other duties (1), Standby at the station (14), Emergency response (3)	70.0	77.9	80.0	84.7
2	Firefighter training (4), Standby at station (20)	66.5	74.4	77.3	82.1
3	Shift handover (0.5), Equipment checks (0.5), Standby at station (14), Emergency response (10)	71.5	79.1	80.3	84.9
4	Shift handover (0.5), Equipment checks (0.5), Other duties (0.5), Standby at the station (22), Emergency response (0.5)	66.1	74.0	78.4	83.1

* Worst-case scenarios calculated using 10th percentile noise levels (MOEL criteria) from Table 5 and assuming exposure at 10th percentile levels during task durations.

).

4. Discussion

This study is the first to conduct task-specific personal noise exposure assessments among Korean firefighters and has the largest sample size (115 firefighters) to date. Several previous studies have attempted to quantify noise exposure in firefighting settings by analyzing task-specific noise levels. While the number of participants and task classifications varied, a common approach was to assess noise during typical duties such as emergency responses, equipment checks, and station-based tasks. For example, both Kang [19] and Lee et al. [23] identified emergency responses and equipment-related activities as significant noise sources, whereas Kang further included standby and office work as separate categories. Reischl et al. [18] provided a more nuanced categorization, highlighting operational situations such as Code-3 responses and fire scene noise, as well as in-vehicle and background station noise. Similarly, Neitzel et al. [38] reported that when noise levels were aggregated across tasks and durations, predicted exposures often exceeded occupational limits. Collectively, these studies emphasize that firefighting noise exposure is highly task-dependent and may frequently surpass recommended thresholds, especially when multiple duties are considered cumulatively. Studies by Kang [19] and Neitzel et al. [38] relied on firefighters’ individual activity logs, resulting in limitations in accurately classifying task durations. However, this study effectively utilized the fire station’s official recording system to accurately classify firefighters’ tasks and their durations by obtaining detailed dispatch times, return times, and specific work activities. In addition, we used firefighters’ individual activity logs, enabling more precise task categorization. Consequently, the 24 h tasks performed by firefighters could be accurately classified. Routine firefighter tasks include shift handovers, equipment checks, education, and other duties. Upon arrival, firefighters conduct a shift handover with the previous shift, followed by equipment checks of vehicle sirens, communication devices, and other gear with the current shift. At this time, rescue personnel inspect rescue equipment separately, firefighters in fire suppression roles inspect pump vehicle engines, and EMS personnel inspect medical equipment in ambulances according to job-specific tasks.

In this study, dispatches performed by firefighters during fire suppression included relatively minor incidents such as fence fires, air conditioner outdoor-unit fires, indoor gas stove fires, balcony fires, and dispatches due to false alarms or cases resolved prior to arrival. Kirkham et al. [4] reported that sirens were generally not activated during routine, non-urgent dispatches, nor were they activated when returning after incidents had resolved. In the present study, we could not classify based on siren use. However, if noise levels had been classified by siren usage, noise levels during dispatches with activated sirens would likely have been higher than those observed.

The results of this study showed that the range of 8 h time-weighted average noise levels by job role was 62.5–71.4 dBA according to MOEL criteria and 74.2–81.2 dBA according to ISO criteria. Lee et al. [23] assessed five Korean firefighters over 24 h and reported an average noise level of 65.3 dBA (MOEL criteria) and 76.0 dBA (American Conference of Governmental Industrial Hygienists [ACGIH] criteria), not exceeding exposure limits. However, peak exposures reached as high as 119 dBA during dispatches, with some instances exceeding the 140 dBC peak noise criterion, aligning with the findings of the present study. Kang [19] conducted personal noise exposure assessments among eight Korean firefighters. Although average noise levels ranging from 79.5 to 84.6 dBA did not exceed the ISO exposure limit of 85 dBA, 5 out of 24 samples (21%) exceeded this limit. Rackl and Decker [39] reported exposure to high noise levels due to engine and siren noise (electric and motor-driven types), yet noise levels did not exceed Occupational Safety and Health Administration (OSHA) exposure standards. Root et al. [21] conducted noise exposure assessments on 93 firefighters during training activities, reporting average noise levels between 77 and 81 dBA, not exceeding the ACGIH exposure limits. However, most rescue equipment training and siren noise levels have been reported to be very high. Kirkham et al. [4] assessed noise exposure among 40 firefighters, reporting an average noise level of 80.9 dBA, with vehicle-specific (pump, ladder, quint, ambulance) noise levels ranging from 78.8 to 82.3 dBA, not exceeding ACGIH limits. However, the peak noise levels exceeded 140 dBC in 69% (78 of 113 samples). Tubbs [22] reported noise levels between 60 and 82 dBA, not exceeding OSHA exposure limits; however, noise levels up to 109 dBA were measured during Code-3 operations at one-minute intervals. Kang et al. [35] measured average noise levels of 77 dBA among seven firefighters, and Neitzel et al. [38] reported noise levels between 69.5 and 83.4 dBA for routine in-station tasks. In contrast, Reischl et al. [18] evaluated eight firefighters’ 8 h time-weighted average noise levels, reporting levels ranging from 84.6 to 98.4 dBA based on OSHA criteria, with all but one firefighter (Truck Tillerman) exceeding the 90 dBA exposure limit. Most studies have reported that firefighters’ average noise levels are not excessively high. Although some studies have reported average noise levels exceeding exposure limits, most studies have emphasized that firefighters commonly experience short-duration but high-intensity noise exposure, noting their relationship with hearing loss.

Furthermore, firefighters have been reported to experience high noise levels at fire scenes [3]. During structural fires, firefighters may be exposed to elevated noise levels owing to alarm activations, fire entry and suppression, and overhaul activities; noise levels can be amplified when working in enclosed spaces. Because no significant building fires occurred during this study, the noise levels for fire suppression tasks may have been slightly underestimated. Command vehicles were dispatched 18 times, primarily for minor incidents such as fence fires, air conditioner outdoor-unit fires, indoor gas stove fires, and balcony fires. Moreover, the high temperatures at fire scenes may technically exceed the operational temperature range of commercially available noise dosimeters.

In this study, ambulances had the highest number of dispatches, with 73 calls (8.1 calls per shift), followed by pump vehicles with 51 calls (5.7 calls per shift), rescue vehicles with 43 calls (4.8 calls per shift), and command vehicles with 18 calls (2 calls per shift). Kirkham et al. [4] reported that rescue vehicles had the highest average dispatch frequency at 3.7 calls per shift, followed by pump vehicles (2.3 calls), quint vehicles (1.6 calls), and ladder vehicles (0.7 calls). Noise levels were similar, although rescue vehicles had the highest level at 82.3 dBA; although dispatch frequency was hypothesized to influence noise exposure, this study did not observe statistically significant differences.

Kirkham et al. [4] and Kang [19] reported differences in noise levels according to specific tasks performed (drivers vs. onboard firefighters). We found that onboard EMS firefighters had significantly higher noise levels than drivers (p < 0.05). Other job types showed no significant differences, though drivers were more often experienced peak noise over 140 dBC. According to current Korean regulations, a hearing conservation program is mandated only when noise exposure exceeds 85 dBA or if NIHL occurs in the workplace [40]. Kang [19] reported that only 5 out of 24 data points exceeded 85 dBA, indicating that most noise levels were below this threshold. Based on the MOEL criteria, this research found no cases exceeding 85 dBA; thus, under current regulations, firefighters would not qualify for a mandated hearing conservation program. However, under the ISO criteria, approximately 10% (11 of 115 samples) exceeded 85 dBA, and approximately 3% (4 samples) exceeded 90 dBA. Although the numbers were not high, some samples exceeded the ISO criterion of 85 dBA. We recommend that the MOEL consider expanding the criteria for hearing conservation program implementation to include occupations characterized by intermittent but high-intensity noise exposure, such as firefighters. Hearing conservation programs should include noise exposure assessments and corresponding engineering controls to reduce noise exposure. Furthermore, these programs should incorporate the provision and mandatory use of hearing protection devices (HPDs), along with education and training on the risks and management of noise exposure.

Several studies have introduced engineering measures aimed at noise reduction. Górski [41] reported that installing sirens within a vehicle near the engine compartment rather than on top could reduce the noise exposure for firefighters inside the vehicle. However, the study mentioned potential safety issues for firefighters, as siren sounds might not propagate sufficiently far in emergencies. Conversely, Park and Han [42] reported the development of Korea’s first high-output directional siren, which could prevent accidents involving vehicles and pedestrians during dispatches, while simultaneously reducing noise exposure for firefighters inside vehicles. Saleh et al. [43] installed sound-dampening mats inside vehicles, which effectively reduced noise levels for drivers, whereas Park and Lee [44] reported that installing low-density Polyurethane (PU) foam in ceilings, floors, and doors of fire vehicles moderately reduced noise but provided no substantial noise reduction.

Awareness regarding hearing protection among Korean firefighters is very low. Most Korean firefighters participating in this study did not use hearing protection devices, and only a few used them during equipment checks. The literature also indicates low awareness and usage rates of hearing protection devices among firefighters [1,3]. Nevertheless, the use of hearing protection devices is crucial for preserving firefighters’ hearing. On the other hand, firefighters tend to avoid using hearing protection devices because they impede effective communication among coworkers and are uncomfortable to wear. Because firefighters require clear communication during dispatches, not only via radio but also among colleagues, conventional hearing protection devices alone have limitations. However, with recent technological advancements, communication-capable hearing protection devices have become commercially available [1]. Technologies such as vehicle intercom systems, noise-canceling devices that enable communication despite background noise, and user-friendly custom hearing protection devices are expected to enhance future awareness and use. Therefore, further research on the development of advanced hearing protection devices is necessary to effectively apply these technologies for firefighter hearing protection.

If wearing hearing protection devices during emergency responses is challenging, establishing a culture that encourages firefighters to use hearing protection during noisy in-station tasks, such as equipment checks, is recommended. This is recommended because it is questionable whether firefighters can practically use protective equipment inside vehicles en route to emergency scenes [4]. Table 5 classifies the peak noise levels by task. Unexpectedly, emergency responses accounted for only 19.6% of instances exceeding 140 dBC during the 24 h work period, whereas in-station tasks and standby at the station accounted for 34% and 46.4%, respectively. Standby at the station accounted for the largest proportion (66.1%) of the 24 h period. This implies that firefighters on standby at stations may also be exposed to high noise levels from other teams’ training or equipment checks. This is because most equipment checks and training activities occur within the station premises. Therefore, it is advisable to use hearing protection during in-station activities that generate noise, such as training or equipment checks. This could significantly enhance hearing protection. In this study, equipment checks were conducted for an average of 56 min per 24 h period. During equipment checks, the maximum average noise level was 93.8 dBA under MOEL criteria and exceeded 100 dBA (107.6 dBA) under ISO criteria. Kang [19] reported similar equipment check durations of about 50 min, with higher average noise levels (86.0 dBA) compared to this study, and recommended wearing hearing protection during such equipment checks.

Considering that firefighters experience irregular noise exposures—short in duration but high in intensity—applying a 3 dB exchange rate may be worth considering. Using a 3 dB exchange rate makes the assessment more sensitive to noise exposure. In other words, the allowable exposure duration decreases. For example, at 115 dBA, the allowable exposure duration would be approximately 15 min under the MOEL criteria but only approximately 28 s under the ACGIH criteria. Thus, for occupations such as firefighting with high noise exposure, using a 3 dB exchange rate is suggested to avoid underestimating noise exposures.

Daniell et al. [45] noted that noise level assessments vary based on the applied exchange rate, highlighting the necessity of a 3 dB exchange rate, as applying a 5 dB exchange rate may underestimate actual noise exposure. Neitzel et al. [38] presented similar findings. The study reported that using a 5 dB exchange rate resulted in a noise level of 82.8 dBA, whereas applying a 3 dB exchange rate increased it to 89.7 dBA. Kang [19] evaluated task-specific noise exposure for 24 Korean firefighters and reported that 21% (5 firefighters) exceeded exposure limits. This study applied a 3 dB exchange rate, with an overall average noise level of 84.1 dBA during emergency responses, which is higher than the 74.6 dBA reported for emergency responses in the present study. When using a 5 dB exchange rate in this study, only 3% of firefighters exceeded 80 dBA; however, applying the ISO criteria (3 dB exchange rate) increased this figure to 22%. Although none exceeded the exposure limits according to the MOEL criteria, 13% exceeded the limits under the ISO criteria. Currently, the exchange rate applied in noise assessments in Korea is 5 dB, which is identical to that used by the OSHA in the United States. When establishing future noise reduction plans for irregular noise exposure occupations, such as firefighting, it is recommended to apply a 3 dB exchange rate to better account for short-duration, high-intensity noise exposures.

Comparing station noise levels, Neitzel et al. [38] reported levels of 66.7 and 68.4 dBA; Reischl [18] reported levels of 40 dBA; Tubbs [46] recorded levels of 70 dBA; and Kang [19] found levels of 63.3 dBA. In this study, the average noise levels at the three fire stations were 52.7 dBA (maximum 66.0 dBA), which was comparable to or lower than those in previous studies. Stephenson et al. [47] noted that noise levels below approximately 75 dBA are considered low enough to allow sufficient hearing recovery. However, standby at the station accounted for 26 occurrences exceeding the peak noise level of 140 dBC, representing a higher proportion (46.4%) compared to other tasks, including emergency responses. In this study, peak noise exposure patterns occurred over brief durations (mostly approximately one minute). Thus, these elevated peak levels were likely due to firefighters passing near noise sources or other factors, such as impacts or excessive pressure on the dosimeter. Collectively, these findings suggest that firefighters may be exposed to high noise levels even during standby at stations. Therefore, it is recommended that noisy tasks be clearly identified and that hearing protection devices be used during these tasks.

Although the average noise levels for firefighters in this study did not exceed exposure standards, it is difficult to conclude that firefighters are free from the risk of hearing loss. This is because firefighters may be intermittently exposed to brief but high-intensity noise owing to the frequency of daily emergency responses, siren activations, and rescue equipment operations during each shift. Noise levels in the study [38] were categorized according to specific tasks. Several scenarios based on the noise levels for each task indicated that noise exposure could exceed standards under certain conditions. They assessed noise levels for each task performed by firefighters, and when they created scenarios based on noise levels firefighters could realistically experience during those tasks, many scenarios exceeded the noise exposure limits [38]. However, this study employed task-specific average durations and 10th percentile noise levels to assess worst-case scenario noise exposure. Noise levels of worst-case scenarios did not exceed exposure limits; however, they did exceed 80 dBA (ISO), which is the lower of the exposure action values [48]. Numerous studies have consistently reported correlations between firefighter noise exposure and hearing loss [3,16,18,22,24,25,26,29,30,31,32,49].

5. Conclusions

In this study, Korean firefighters exhibited relatively low average noise levels; however, when classified by specific tasks, their exposure was sufficiently high enough to potentially cause hearing loss. Given the high standards required in occupational health, we recommend that in cases of short-duration but high-level noise exposure, it is necessary to apply a 3 dB exchange rate to ensure a more stringent assessment. Despite their exposure to short-duration high-intensity noise, most firefighters do not use hearing protection devices [17]. It appears necessary to establish a culture among firefighters that encourages the use of hearing protection. Furthermore, according to data on compensated occupational diseases among Korean firefighters from 2010 to 2015, only 8 firefighters (0.4%) out of 2154 total cases were compensated due to hearing loss [50].

Hearing loss due to noise exposure is a preventable risk factor. Successful management of this risk factor can maintain good hearing for extended periods, prevent NIHL, and reduce associated medical expenses [51]. Numerous studies have shown that hearing loss in older adults is significantly associated with increased risks of social isolation and loneliness, which in turn contribute to cognitive decline, depression, and increased healthcare costs [52]. Because NIHL is difficult to diagnose in its early stages, managing noise exposure and raising personal awareness are crucial [32]. Noise exposure is often mistakenly regarded as an acceptable risk factor. However, as previously mentioned, hearing protection is essential. This situation is analogous to when a self-contained breathing apparatus became mandatory in firefighting. A shift in perception is needed to recognize hearing protection devices as essential gear for firefighters [1]. The effectiveness of hearing conservation programs for firefighters has been demonstrated to a certain extent [53]. Therefore, enhancing awareness, developing a culture, and establishing consistent practices are necessary. It is necessary to raise awareness among Korean firefighters regarding the risk of hearing loss, develop practical measures for using hearing protection devices, and establish a suitable hearing conservation program tailored specifically for firefighters.