3.2.5. Degree of hearing loss in each ear in the study groups before and after intervention
Table 3.34. Degree of hearing loss by ear in the study groups
SGTL
Intervention group (n = 100) | Control group (n = 100) | p (1,2) | |||||||
Before CT | After CT (1) | Before CT | After CT (2) | ||||||
n | % | n | % | n | % | n | % | ||
Right ear | |||||||||
Normal | 100 | 100 | 98 | 98 | 100 | 100 | 81 | 81 | 0.0001 |
Light | 0 | 0 | 2 | 2 | 0 | 0 | 17 | 17 | 0.0001 |
Fit | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 2 | |
Heavy | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
left ear | |||||||||
Normal | 100 | 100 | 97 | 97 | 100 | 100 | 78 | 78 | 0.0001 |
Light | 0 | 0 | 3 | 3 | 0 | 0 | 20 | 20 | 0.0004 |
Fit | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 2 | |
Heavy | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
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The level of hearing loss in each ear after intervention between the two groups was significantly different at mild (21 - 40dB) and moderate (41 - 60dB).
3.2.6. Tympanometry before and after intervention
Table 3.35 . Tympanometry before and after intervention
Tympanometry
Right ear (n = 100) | left ear (n = 100) | ||||||||
d1 | d2 | d1 | d2 | p | |||||
Before | After | Before | after | Before | After | Before | after | ||
A | 96 | 96 | 98 | 97 | 95 | 96 | 97 | 97 | >0.05 |
Ad | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | >0.05 |
As | 2 | 2 | 1 | 0 | 2 | 2 | 1 | 0 | >0.05 |
B | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | >0.05 |
C | 1 | 1 | 1 | 0 | 1 | 1 | 2 | 0 | >0.05 |
Tympanometry before and after intervention did not change, the majority were type A showing normal middle ear morphology and function.
On the other hand, the audiogram in cases of hearing loss is sensorineural deafness, due to the impact on inner ear function.
3.2.7. Hearing loss levels in groups before and after intervention
Table 3.36 . Hearing loss levels in the two study groups before and after intervention
Hearing Intervention group Control group RR
(n = 100) (n = 100) (1,2)
Before CT
After CT (1)
Before CT
After CT (2)
95% CI
n | % | n | % | n | % | n | % | ||
Normal | 100 | 100 | 96 | 96 | 100 | 100 | 74 | 74 | |
SGTL1 side | 0 | 0 | 3 | 3 | 0 | 0 | 11 | 11 | |
SGTL 2 sides | 0 | 0 | 1 | 1 | 0 | 0 | 15 | 15 | |
Total SGTL | 0 | 0 | 4 | 4 | 0 | 0 | 26 | 26 | 0.15 |
(0.06- |
0.42)
There was a significant difference between the two groups after intervention in the number of SGTL. The rate of SGTL in the control group was 26% and in the intervention group was 4% with a difference of p < 0.001.
- SGTL rate after intervention of the intervention group: 0.04
- SGTL rate after intervention of the control group: 0.26
- Relative risk RR= 0.04
0.26
x 100%= 15.38%
The relative risk of hearing loss was 15.38% (RR 95%CI: 0.06-0.42), or an 84.62% reduction in hearing loss in the intervention group compared with the control group.
CHAPTER 4: DISCUSSION
Noise-induced hearing loss has been known for several hundred years and remains a worldwide problem. The WHO estimates that 16% of adults have hearing problems due to occupational noise exposure. [80]
Exposure to harmful noise in industry, the military and some other jobs can cause some adverse health problems for those exposed, but we can take proactive measures to prevent it.
4.1. Current status of noise, hearing loss and related factors in armored forces in 2017
4.1.1. Noise status
The main source of noise comes from the vehicle's engine, the closer to the tank or the vehicle's surroundings, especially near the engine's exhaust pipe, the higher the noise intensity.
The overall noise intensity measured on the armored vehicle training ground was 76.08±25.66 dB. With the measurement locations and times (a total of 105 noise intensity measurement points), 4/7 locations and 60.95% of measurement points had an intensity exceeding the allowable threshold (>85dB). This result shows that the training environment of the research group is mostly affected by harmful noise. Especially in the positions inside the vehicle, when the vehicle accelerates, when firing artillery shells, 100% of measurement points have sound intensity exceeding the safety threshold. In which, the sitting position in the vehicle when the vehicle is running is the highest, the measured sound level is 111 dB, followed by the position in the vehicle when the vehicle is running on the spot with the highest sound level measured at 102 dB, the position where the vehicle is running on the spot and firing live ammunition at a distance of 200m, the recorded sound intensity all exceeds the threshold of the measuring device (>120dB). The farther away from the vehicle engine, the lower the noise level. Therefore, working in an environment close to armored vehicles with loud noise will have a significant impact on health in general and hearing in particular. We have conducted measurements
The ability to reduce noise levels of helmets from 20-25dB depends on the quality of the helmet and the correct fastening of the strap. Thus, with the highest measured sound level when the vehicle is running at 111dB, if the crew members wear helmets that ensure quality and wear helmets according to regulations, the noise level will be reduced below the harmful level (<85dB). On the contrary, those who do not comply with the regulations on wearing hearing protection helmets when standing in the vehicle will be directly exposed to harmful noise. When conducting research on the subjects of the Armored Corps, including: commanding officers, instructors, crew members, repair staff. There are subjects who, when instructing students, often do not wear protective helmets because it is difficult to communicate. On the other hand, in certain cases, they need to listen to the sound of the vehicle engine to make a preliminary judgment on the condition of the vehicle to help repair damaged parts. In these cases, they are the subjects directly exposed to harmful noise as mentioned above.
Regarding the noise of tanks and armored vehicles, there are very few research documents on the noise of these vehicles. Ho Xuan An (2003) measured the noise of 3 types of vehicles (T54, PT76, K63) and showed that all 3 types had a wide spectrum of noise, in 8 main frequency bands according to the measurement locations, all exceeding the allowable threshold from 8-30 dB, especially when the vehicle was running and the doors were closed. At frequencies of 4000Hz and 2000Hz, both had high intensities exceeding the allowable threshold [5]. Author Ho Xuan An did not give the ratio of noise locations exceeding TCCP, however, the author also concluded: depending on the location, the measured noise intensity ranged from 90-115 dB with the ratio of low frequency noise being higher than high frequency [5]. Compared with author Ho Xuan An, our results had a wider noise intensity range from 45dB to above the measurement level of the machine (>120dB). This can be explained by the fact that the noise measurement location in our study was at many locations and times that author Ho Xuan An had not done, for example, the location 200m away when the car was running and standing still, the car was running and standing still while firing live ammunition... In our study, the location 200m away from the car was within the safe threshold with
hearing. Therefore, in this position, it may not be necessary to wear a hat or earplugs to prevent the harmful effects of noise. On the contrary, at the measuring position 200m from the vehicle engine when the live ammunition was fired, the measured sound intensity all exceeded the threshold of the measuring device. This is a warning that even though standing at a fairly long distance, hearing protection is still necessary.
Nguyen Thanh Quan (2011) [12] "Research on the impact of noise on hearing of employees working in a noisy environment at Noi Bai airport", the number of noise samples exceeding TCCP according to the general noise intensity at the research facility is 77/98 (78.6%). The average general noise intensity of the study is 88.4 ± 6.3dB. The author studied the impact of noise in many areas with specific characteristics such as the passenger service area, 100% of the samples are below TCCP because this area is partially soundproofed by a glass wall system from other areas and far from the take-off and landing area. The average general noise intensity of the locations with noise exceeding TCCP is 90.6 ± 4.8dB. The parking area has the highest average of 93.2 ± 4.7dB, the luggage area 87.8 ± 1.7dB, the factory area 86.9
± 3.2dB. In our study, the number of noise samples exceeding TCCP and the average overall noise intensity of 60.95% and 76.08 ± 25.66 are lower than those of author Nguyen Thanh Quan. This may explain the nature and location of the author's research on noise from civil aircraft and at airports, so the nature will be different from that of tank engines and training grounds. However, in the study, author Nguyen Thanh Quan divided the areas according to the characteristics of aviation, so the safe distance from harmful noise has not been mentioned. Once again, it is possible to determine the location at 200m away, the noise from tanks is no longer harmful to hearing.
Nguyen Hoang Luyen (2017) [9] when studying the working environment conditions of submarine sailors, found that when the ship in port did not operate diesel engines, most of the noise intensity measurements met the TCVSLD standards (99%). However,
However, when the ship operates at port and operates a level 4/5 diesel engine, 100% of the samples measured in the engine compartment do not meet the labor standards, the measured noise intensity is 106.6dB. Thus, although different in means, the common characteristic is that the noise in "closed" spaces is at a dangerous level for the hearing of soldiers. Nguyen Van Chuyen (2017) [13] when studying the working and living conditions of naval sailors on Gepard-class escort ships also determined that the engine room is the place with the greatest noise pollution, the ship runs on a generator with a noise of 121.7dB, when the ship operates on a voyage, the noise intensity is 132.4dB at an ear-sore level.
With foreign military studies: information on noise sources and noise levels in military environments is diverse. Sound intensity varies depending on the distance from the sound source and how the sound is generated. Important noise characteristics include not only the peak sound pressure level but also the pulse shape and frequency. On aircraft carriers, flight operations generate a lot of noise [121]. Below deck on aircraft carriers, noise levels of 106 dB were measured during aircraft launches. Exposure to high noise levels has been reported for positions such as flight controllers and air traffic control technicians and cryptographers in the Navy and Air Force [23],[61],[64],[81]. Additionally, military personnel may be potentially exposed to noise from noisy equipment and activities in industrial environments, such as the operation of heavy equipment [113]. Examples of noise levels related to military equipment and weapons clearly show that there are many noise sources in the military environment that exceed the permissible standards. Our study has results close to some studies by authors such as Sunde (2015) investigating noise pollution on Norwegian naval ships, finding the overall noise intensity to be 89.9 ± 4.9dB [100].
In general, the noise emitted by tanks is at a level that is harmful to hearing because the collected data mostly exceeds the TCCP, especially in the area around the vehicle and when the vehicle accelerates and fires live ammunition. The general noise intensity and noise range are consistent with the publications of domestic and foreign studies. Through the research results, the distance of 200m when the vehicle is running is safe for hearing, however, it should be noted that when firing live ammunition, a hearing protection plan is needed. The actual noise data provides further evidence of the relationship between hearing loss and harmful noise exposure in armored personnel.
Limitations of the research results: the noise intensity at the time of live ammunition firing has not been measured because it exceeds the measurement threshold of the machine (> 120dB). The noise of tanks in the repair area has not been measured because the actual conditions were only measured on the training ground. There is no noise data for other representative vehicles of the Armored Corps: PT76, BMP, BTR, M113, T72. The reliability of the data is affected by the noise collected only from the T54 tank. However, this is the most commonly used vehicle of the Armored Corps today.
4.1.2. Current status of hearing loss
4.1.2.1. General characteristics of the research group
The average age of the research group: 38.67 ± 5.8, the lowest age: 21 and the highest: 52. The average age of the research group: 18.94 ± 5.6, the lowest age: 2 years and the highest is 35 years. Most of the soldiers have a relatively long time of service in the military, with many positions such as teaching staff in departments and offices, directly training students on the training ground, participating in repairing tanks and armored vehicles... Hearing loss in old age is also called presbycusis. However, it is difficult to distinguish presbycusis from general deafness because there are many other causes such as prolonged exposure to harmful noise. Most elderly people combine both presbycusis and noise-related deafness. Each year,