Following the explosion of a chemical plant in France, a study was conducted to analyse the relationship between hearing thresholds and distance from the explosion based on post- and pre-blast audiometric data, and to describe the functional symptoms and visits for hearing problems.
Audiometric tests with standard procedure of 511 workers of a company located near the explosion were proposed and conducted by the occupational medicine department after the explosion. Past occupational noise exposure, past medical history of ear problems, distance from the explosion, functional symptoms and visits for hearing problems following explosion and results of past audiometric tests if available were collected. Workers were classified as “exposed” or “less exposed” according to the distance from the explosion. Mean decibel threshold shifts for each ear were analysed by frequency with Student’s t test and by multiple linear regression taking into account confounding factors.
Of a total of 425 (83%) of the firm’s workers who participated in the study, 49% had received an audiometric test before the explosion. Hearing shift between pre- and post-explosion audiograms was significantly greater for the “exposed” group than for the “less exposed” one at 2,000 and 4,000 Hz (P < 0.05, P < 0.001, respectively) and borderline at 6,000 Hz (P = 0.09) for the right ear and at 2,000 (P < 0.01), 6,000 and 8,000 Hz (P < 0.05) for the left ear. Among those of the “exposed” workers who reported any functional symptom following the explosion, 45% did not visit an ENT specialist despite these signs.
The study demonstrated statistically significant hearing shift from 2,000 to 6,000 Hz in relation with distance from the explosion and showed that even when functional symptoms were present, people did not necessarily seek medical advice. Screening for hearing loss should be recommended for people most exposed to excess acoustic pressure, in order to offer them prevention advice.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.