There are few published international studies on the effects of ship noise on seafarers’ hearing (9).
We should remember that if a person is exposed to noise greater than 80 dB(A) for 8 hours per day or more, this can harm the inner ear, bilaterally and more or less symmetrically, and this damage will worsen as the period of exposure lengthens and will affect higher frequencies, primarily 4000 Hz. This is permanent endocochlear perception hearing loss in the context of chronic auditory fatigue.
On board merchant ships, as we have seen, engineers are exposed to the most noise, with equivalent average levels generally being above 85 dB(A). An audiometry study carried out in 1983 (10) concluded that there was a small region of hearing loss at 4000 Hz in merchant ship engineers, which was most noticeable in those over 40. Seafarers involved in other occupations were not affected.
Fig 1: audiometric curves of Marine engineers by ages (Median values,
combined results from both ears).
At similar ages, onboard engineers had noticeably less hearing loss than did subjects who worked in noise levels of 95 dB or 100 dB 8 hours per day.
In a more recent study, Parker (11) found hearing loss in 26.8% of engineers, compared with 16% of deck crew members and 9.9% of supervisors (these differences were statistically significant).
The moderate levels of hearing loss observed in engineers may be explained by the fact that their exposure to engine noise is tempered by soundproofing of the control cabins in merchant ship engine rooms, which means that exposure to significant noise is confined to routine patrols and maintenance tasks, and the fact that they wear ear protection when carrying out such tasks. If the noise is constant or only slightly fluctuating, this can also moderate its effects. If work is distributed throughout the year in the form of 2-3 months of work followed by a holiday of the same length, this is a significant factor responsible for the moderate nature of this hypoacusis.
Nevertheless, in a recent study (2008), Kaerlev et al. (12) found that, compared to other seafarers, the engine room personnel have a relative risk ratio of 2.39 for hearing loss among Danish seafarers.
The situation on board fishing boats, however, is very different. As we have already noted, Andro and Dorva (l7) have shown that seafarers on board high-sea fishing vessels are subjected to constant noise levels 24 hours a day. If we take a “median” vessel, we see that seafarers are exposed to 84-86 dB when working on deck, 76 dB when on gangway watch and 82 dB when resting in the crew quarters. In parallel with this audiometric study, a similar study was carried out on 113 fishermen on board the same type of vessel
Fig 2: Comparison of audiometric curves between Marine engineers and workers exposed to 95dB (by ages)
(13). The results showed that there was noise-related hearing loss with a window of hearing loss at 4000 Hz, which worsened with age and length of service. The hearing deficits were compared with the French standard NF S 31-013 which contains estimations from international epidemiological data concerning hearing in workers over 40 years old who had been exposed to quasi-stable levels of industrial noise, at 90, 95 and 100 dB, for 20 years. Hearing deficit for fishermen (aged 40, 23 years of exposure) lay between levels of deficit for standardised subjects exposed to 90 dB and those exposed to 95 dB in terms of high frequencies, and were still greater for low frequencies.
A continuous noise level of 85 dB 24 hours a day, as experienced by fishermen, is calculated as equivalent to a continuous noise level of 90 dB over 8 hours. In other words, a seafarer who experiences 85 dB 24 hours a day has hearing loss equivalent to that of a worker exposed to 90-95 dB of factory noise 8 hours a day. These results clearly show that high-sea fishing is an occupation that carries a risk of hearing loss due to noise.
Fig 3: Comparison of audiometric curves between fishermen, industrial workers
exposed to 90 dB (8h per day) and witnesses.
This risk has explicitly been recognised in the report by the European Parliament on safety and accidents in sea fishing, dated 12 March 2001: “Incessant noise creates an aggressive climate on board and means that fishermen sleep little and badly, making it difficult for them to obtain the rest they need... A separate topic concerns fishing-related diseases, which are prevalent among fishermen. Furthermore, this risk is explicitly recognised in the European Parliament report dated 12 March 2001 concerning safety and accidents in sea fishing, which notes that incessant noise creates an aggressive climate on board and means that fishermen sleep little and badly, making it difficult for them to obtain the rest they need, and they can also be affected by hearing loss.
The results of the study by F Trecan (14) involving 18,000 audiography tests on French seafarers confirm the findings of the previous studies. This study confirms that fishermen are at greater risk than commercial seafarers. In maritime transport, seafarers on board oil tankers and cargo ships are observed to be at the greatest risk. Kaerlev (12) finds also an increased risk for fishermen.
The problem with noise on fishing vessels is one of individual protection; as we have seen, in current standard practice, vessels do not have specific soundproofing. Individual protection could be effective (15), but the fisherman would have to wear it 24 hours a day, which is not practicable, although it could potentially be possible to wear custom-made earplugs constantly. For all vessels, the only valid improvement would be soundproofing of quarters when the vessel is built.