An epidemiological study was developed to take into account specific employee habits while measuring the possible prevalence of hearing problems arising from earlier occupational exposure. During 30 years of war, Angolans were exposed to high levels of noise, a factor exacerbated by the offshore environment many workers now share. A population of nonexposed staff, largely administrative, was compared with a population of offshore workers. The results did not show any significant difference in hearing capabilities.
Introduction
Noise-induced hearing loss (NIHL) is the most prevalent irreversible industrial disease, and noise is the most prevalent compensable occupational hazard. In developing countries, occupational noise and urban environmental noise are increasing risk factors for hearing impairment, which may lead to increased incidence of accidents at work.
Unlike most other occupational injuries, NIHL occurs without any visible exterior evidence or trauma and is perceived too late. While irreversible, it is fully preventable with proper job design, training, and protection measures. The estimated cost of noise to developed countries ranges from 0.2 to 2% of gross domestic product. However, there is a lack of accurate epidemiological studies on prevalence, risk factors, and costs of NIHL, particularly in developing countries.
In an audiogram, the decrease in the hearing threshold is detected at an early stage, allowing preventive measures to be taken. Changes in audiometric tracings are common and usually bilateral. Changes in the hearing threshold involve an initial notch at high frequencies of 3,000, 4,000, and 6,000 Hz, which, over 10 to 15 years of exposure, reach a maximum of 75 dB. Thereafter, medium and low frequencies are gradually affected up to a maximum of 40 dB.
Noise-Exposure Risks in Angola
Social and Environmental Exposure. During the civil war that ended in 2002, people were exposed to high noise peaks from gunfire, explosions, and tank battles. Throughout this period, no medical assessments or epidemiological data were available. There is no public law on noise pollution, and, in Luanda, nightclubs play loud music throughout the night from Thursday until Monday. Common transport buses have powerful sound systems, exposing drivers, riders, bystanders, and other commuters in numerous traffic jams to noise peaks. Traffic in Luanda during the week is heavily congested, and there is a constant cacophony of car horns and car alarms. Industry workers are exposed to noise during offshore drilling and production operations, onshore logistics operations, and air travel. Currently, there is no national labor legislation enforcing noise limits.
Total E&P Angola (TEPA) Rule. Table 1 provides limits based on European Directive 2003/10/EC concerning noise. In zones where the normal single-ear protection of the worker cannot reduce the noise below the occupational exposure limit (OEL) of 87 dB(A), double hearing protection is made mandatory by display of the safety sign in Fig. 1.
Hearing-Conservation Program
TEPA’s program consists of the following actions: an epidemiological study, noise and vibration studies on offshore facilities, direct and individual monitoring campaigns with noise mapping, noise-awareness campaigns, and mandatory audiometry during an offshore medical exam.
Epidemiological Study. The cross-sectional study was conducted from August to October 2010 in Luanda. Subjects included Angolan offshore workers and a comparative group comprising administrative employees from offices in Luanda. Statistical software was used. A confidence interval of 95% with a beta error of 20% was accepted, with a 16% prevalence of hearing loss in the nonexposed group and a 2:1 exposed/nonexposed ratio in the proportion of 91:46. Simple random sampling was used for the offshore group, and paired samples matched by age were used for the administrative group. The study involved 164 employees (113 offshore, 51 administrative). Twenty-seven workers were eventually excluded from the statistical analysis. The analysis phase considered 92 (44%) out of 209 Angolan offshore workers and 45 (6%) out of 736 Angolan administrative workers, all male.
For the audiological assessment, a minimum of 14 hours of auditory rest was recommended before the audiometric test in order to reduce the possibility of a temporary drop in hearing threshold. Participants responded to an individual questionnaire about their family and personal history of hearing disease, lifestyle, and exposure to noise (both nonoccupational and occupational), and aired any hearing complaints. A bilateral inspection was conducted of the outer ear, the external auditory meatus, and the tympanic membrane. Hearing tests were followed directly by a screening for hearing abnormalities by a practitioner in general and family medicine. The audiograms were then interpreted by a specialist in occupational medicine.
Data were processed using statistical software. For continuous variables, results were expressed as means, standard deviation, medians, and interquartile ranges. Categorical variables were expressed as frequencies and percentages.
Sociodemographic Characteristics. The population consisted of very young adults, 82% having worked at the company for less than 10 years; nearly half were younger than 30, and 82% were younger than 40. Nearly half the offshore population had been working at the company for less than 4 years, while half the administrative group had been working there for 2 years or less, indicating a statistically significant difference. Fig. 2 represents the distribution of the offshore group by activity, according to homogeneous exposure groups defined by the company.
Audiological Assessment. Table 2 shows the results of the clinical questionnaire, which discusses the medical history and symptoms of hearing disease. In the occupational section of the questionnaire, there were no significant differences between groups in their responses on the use of firearms, military service, motorcycle riding, time spent in noisy environments outside the working environment, and previous hearing tests. The history of prior or current work performed in a noisy environment and the use of or recommendation to use ear protectors was significantly higher in the offshore group.
Comparison of Hearing Thresholds. With respect to the left ear, all mean values in both groups were less than 15 dB and the mean audiometric curves were similar at all frequencies, except at 500 and 8,000 Hz. At all frequencies except 500 Hz, the mean thresholds of the offshore group were slightly higher than those of the administrative group; at 500 Hz, the hearing threshold was significantly lower in the administrative group.
In the offshore group, the mean threshold extremes ranged from a minimum of 6.63 dB at 1,000 Hz to a maximum of 13.75 dB at 8,000 Hz. In the administrative group, the mean threshold extremes ranged from 5.89 dB at 1,000 Hz to 11.11 dB at 6,000 Hz. When we compare the mean curves of both ears in the two groups, we can see that the shape of the mean hearing thresholds matches the previous audiometric curves. When comparing both groups, we notice a significant difference in the median threshold analysis of both ears at frequencies of 500 Hz (p=0.002) and 8,000 Hz (p=0.023).
Results of the Study
The offshore group is young (median=30 years) and has been exposed to occupational noise for a short period of time at the company (median=4 years). The shape of its audiometric curve does not suggest noise-induced hearing loss and, at almost every frequency, is similar to that of the administrative group. In the left ear, a comparison of hearing thresholds (median) between offshore and administrative groups showed no statistically significant differences at frequencies of 1,000 to 8,000 Hz. The audiometric curves were almost flat and identical to each other. In the right ear, results were similar. These findings do not meet the criteria for noise-induced hearing loss (threshold >25 dB) and may be monitored in subsequent studies. With at least one hearing threshold above 25 dB, changes were found in 14% of the offshore group’s audiogram results and in 13% of the administrative-group results, though the difference between the two was insignificant.
Noise and Vibration Studies on Offshore Facilities. An internationally recognized company made noise and vibration studies onboard company floating production, storage, and offloading vessels (FPSOs). The studies resulted in color mappings of all decks in which the noisiest installations were distinguished. These zones on deck were clearly marked with ear-protection safety signs and floor painting. High noise levels are mainly present at pumps, valves, and pipes with turbulent fluid flow; at hydrocyclones and separators; and at compressors, turbines, and generators. Engineering controls to damp down noise and vibration were implemented as a result of the recommendations made in the report.
Direct and Individual Monitoring Campaigns With Noise Mapping. The company Industrial Hygiene Department organizes annual noise-monitoring campaigns consisting of direct monitoring with a Class 2 noisemeter of the produced noise in decks, offices, and living quarters. The measurements are then extrapolated onto noise maps by use of specific-color balls in relation to the common personal protective equipment used onboard. Work in high-noise areas for a prolonged period of time requires a special work permit defining the permissible exposure time. Apart from the direct measurements, 10 volunteers from different similar-exposure groups are individually monitored during 5 consecutive days using noise badges registering the noise above 70 dB(A). It is mathematically possible that a worker does not exceed the OEL calculated over the entire shift, but does go beyond the OEL during a part of the shift. For every 3 dB that the OEL plus attenuation from the ear protection is exceeded, the exposure time must be halved. Abseilers, mechanics, and electricians are the main job categories exposed to high noise.
Noise-Awareness Campaigns. During the monitoring campaigns and also during presentations to offshore and office workers, noise-awareness campaigns are organized in French, English, and Portuguese. The purpose is to familiarize the workers with the company’s hearing-conservation program and to ensure that they protect themselves from noise both in the occupational environment and in their time off. Workers are also trained in use of a variety of ear-protection equipment.
Mandatory Audiometry During Offshore Medical Exam. Audiometric testing is an important part of hearing-preservation programs. It allows early identification of employees with increasing hearing deficits and prevention of future NIHL. All offshore workers are obligated to undergo an audiometry during their annual medical exam. Each worker has an individual Health Risk Assessment File that identifies major hazards to the examining doctor. Exposure to high noise levels is stated as one of these risks. At the time of hiring, new employees are also required to undergo an audiometry exam. The data of the audiometry and the results from the noise-risk assessments are stored in a specific databank for 50 years.
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 157292, “Integrated Noise Protection Program—From Noise Measurements to Epidemiology,” by Tania Batalha, Nico De Sadeleer, and Stephan Plisson-Saune, Total E&P Angola, prepared for the 2012 SPE/APPEA International Conference on Health, Safety, and Environment in Oil and Gas Exploration and Production, Perth, Australia, 11–13 September. The paper has not been peer reviewed.