Noise as an explanatory factor in work-related fatality reports.

Noise exposure in the workplace is a common reality in Québec, Canada as it is elsewhere. However, the extent to which noise acts as a causal or contributive factor in industrial work-related accidents has not been studied thoroughly despite its plausibility. This article aims to describe the importance or potential importance, during investigations looking into the specific causes of each work-related fatal accident, of noise as an explanatory factor. The written information contained in the accident reports pertaining to contextual and technical elements were used. The study used multiple case qualitative content analysis. This descriptive study was based on the content analysis of the 788 reports from the Commission de la santé et de la sécurité du travail du Québec [Workers' Compensation Board (WCB)] investigating the fatal work-related accidents between 1990 and 2005. The study was descriptive (number and percentages). Noise was explicitly stated as one of the explanatory factors for the fatal outcome in 2.2% (17/788) of the fatal accidents, particularly when the work involved vehicular movement or the need to communicate between workers. Noise was not typically considered a unique cause in the accident, notably because the investigators considered that the accident would have probably occurred due to other risk factors (for example, disregard of safety rules, shortcomings in work methods, and inadequate training). Noise is an important risk factor when communication is involved in work. Since noise is ubiquitous and may also interfere with vigilance and other risk factors for accidents, it may be a much more important contributing factor to accidents than is currently recognized.

Introduction

“The recognition of noise as a serious health hazard as opposed to a nuisance is a recent development and the health effects of hazardous noise exposure are now considered to be an increasingly important public health problem.”[1] Noise exposure in the workplace is a common reality in Québec (province of Canada) and worldwide. In the USA, it is estimated that 22 million workers (17%) are exposed to hazardous noise.[2] In Québec, two recent surveys[34] have estimated that 7% and 10%, respectively, of Québec's workers reported being currently exposed “often or always” to loud workplace noise “such that it is difficult to maintain a conversation a few feet away, even when shouting.” In addition, among them at least 4,300 workers are exposed to daily noise levels of 100 dBA or more in over 500 workplaces.[5]

Occupational noise and accidents

Occupational noise exposure has been linked to numerous adverse health effects.[6] The assumption of a causal or contributive impact of occupational noise on the occurrence of occupational accidents has been addressed in several studies.[7891011121314] Recent publications except one[15] suggest an exposure-response relationship between noise exposure or hearing impairment and accident risk.[141617181920] According to three explanatory models[212223] and empirical data, there is a biological plausibility for a causal relationship between noise exposure and occupational accident risk.[22242526] These published models have been integrated in a new model [Figure 1]. Ambient noise interference with communication appears as a main plausible pathway.[2127282930] The effect of hearing protection devices (HPDs) on communication interference is inconclusive.[3132333435363738] Other plausible pathways include habituation and reduced vigilance.[30394041] Nevertheless, the extent to which noise does act as a causal or contributive factor in fatal workplace accidents remains unclear and is subject to debate.

Figure 1

Potential effects of occupational noise on the risk of injuries based on interaction between the worker and his/her workplace [Institut national de santé publique du Québec (INSPQ), adapted from Hétu 1993, Wilkins 1981 and Le Cocq 2010]

Through a review of work-related fatality reports, this study sought to: 1. describe the characteristics and circumstances of fatal accidents occurring in noisy workplaces, 2. determine the number of instances when noise was identified as one of the potential causes and retained as such, 3. determine the number of instances when noise could have been identified as one of the potential causes, and 4. examine the methods used in reports to analyze the noise factor during accident investigations. Though not presented in this paper, the fifth aim was to determine the worth of fatality reports as a potential surveillance data source.

Methods

Similar to a multiple case studies design, this population-based descriptive study is based on a thorough analysis of the content found in the 788 fatal accident reports completed by various inspectors from the Commission de la santé et de la sécurité du travail du Québec [Workers’ Compensation Board (WCB)] during the 1990-2005 period. For the investigation of the causes of a fatal injury, the WCB assigns two inspectors to each case. As a more standardized inquiry process was adopted in 2000, the reports were divided into the following two blocks: Main block covering accident reports issued between 2000 and 2005 (n = 284) and a complementary block assessing those in the 1990-1999 period (n = 504).

In brief, the assigned inspectors are responsible for gathering all interesting and relevant facts from various sources (witnesses, simulations, etc.), classifying the information into essential and secondary items, identifying the potential causes to be further analyzed, and reaching a plausible conclusion as to the causes of the fatal event. In this study, assessment of the noise factor was based on the written information found in the publicly available reports regarding the essential contextual and technical elements used to assess the noise-accident relationship.

The underlying framework for analyzing each accident report is presented with the results in Figure 2. Accidents were deemed to have occurred in a noisy environment wherever it was clearly indicated that at least one source of noise was operating within the victim's work area at the time of the accident irrespective of the noise level. To be classified “noise mentioned explicitly,” a report had to contain at least one key word relating to the following categories: Masking noise, warning signal, hearing loss, or HPDs. When mentioned explicitly, noise was classified as treated “directly” when analyzed as a potential cause per se, “indirectly” when analyzed within another potential cause, and “in a general manner” when merely mentioned in the description of the fatal event. Lastly, reports in which noise was identified as an explanatory factor of the fatal event by the inspectors were classified as “noise retained as a cause.”

Figure 2

Noise as an explanatory factor in the Québec WCB fatal accidents reports in the 1990-2005 period (n = 788)

When noise was mentioned explicitly, an in-depth content analysis was first carried out separately by at least two expert authors (audiologists or acoustic engineers) to examine the methods used by the inspectors to analyze the noise factor. Thereafter, during a meeting to discuss individual reports, a consensus was reached by all the authors regarding the inspectors’ choice of noise measurements and whether their analyses and conclusions were appropriate. The number of reports to be analyzed in depth was determined by reaching saturation in the information of interest relative to the study's objectives. All the reports not thoroughly analyzed were reviewed summarily by one of the authors to check for any new relevant information.

A comprehensive analysis of accident reports from the main block in which noise was not mentioned explicitly was also carried out to determine if noise could have been considered as a potential cause. To reach such a conclusion, the accident must have occurred in a noisy environment and involved a victim being “struck by a vehicle” since noise is more likely to interfere with communication in this context.

While reports from the main block were scrutinized for information relative to all four objectives, those from the complementary block were analyzed only when noise was mentioned explicitly (objectives 2 and 4).

Results

From the 788 work-related accident reports covering the 1990-2005 period, noise was mentioned explicitly in 67 (32 + 35/788 = 8.5%) reports [Figure 2]. Among those, noise was treated “directly” in 21 (2.7%) reports, “indirectly” in 15 (1.9%) reports, and “in a general manner” in 31 (3.9%) reports. Moreover, inspectors concluded that noise was one of the causes in the fatal event in 17 (2.2%) out of 21 reports in which noise was analyzed directly.

From the 67 reports in which noise was mentioned explicitly, 50 were analyzed comprehensively, including 28 out of 32 from the main block and 22 out of 35 from the complementary block. The analysis revealed the following four noise assessment methods used by the inspectors:

Qualitative assessment [21 (42%)], 19 of which also included quantitative measures;

Event simulations [13 (26%)], two of which were with expert consultants;

Quantitative measures only [six (12%)]; and

General description only [10 (20%)].

From the available information and despite poor data in some cases (i.e., incomplete noise assessments and technical flaws), the authors concluded that the inspectors had reached adequate conclusions in 24 (48%) cases. However, a more thorough investigation of the fatal event could have yielded a different conclusion relative to the noise factor in three cases (6%). Finally, 23 (46%) reports contained insufficient information for the authors to assess the validity of the inspectors’ conclusions.

During the 2000-2005 period (main block of reports), 161 fatal accidents took place in noisy work environments characterized by various noise sources (trucks, concrete saws, wood saws, conveyor belts, etc.) (Figure 2, “Noisy environment?”). Although in most cases (122/161), the noise source was directly involved in the accidental event, noise per se was retained as a cause in 4.3% (7/161) of cases. Construction (31/161) and forestry (28/161) workers accounted for 36.6% of the victims. The mechanism of injury was “struck by a vehicle” in 47 (29.2%) cases, hit/crushed by an object in 38 (23.6%) cases, or wedged/dragged in 34 (21.1%) cases. The remaining 42 (26.1%) victims fell or were injured by some other mechanism.

Over the same period (2000-2005), noise was not explicitly mentioned in 129 reports investigating fatal accidents in noisy work environments including 29 (22.5%) accidents involving a worker being “struck by a vehicle.” Following a comprehensive content analysis of these 29 reports, the authors concluded that noise could have been considered in five (3.9%) reports because of sufficient circumstantial evidence of possible interference of ambient noise in the communication between workers or in the perception of warning signals. However, the available written information did not make it possible to conclude if noise was actually a cause or not.

In all other reports involving a worker being struck by a vehicle (24/29), the authors agreed with the inspectors’ findings that noise did not need to be considered as other identified causes were sufficiently obvious to explain the event irrespective of the noise levels.

Discussion

Noise was explicitly stated as one of the explanatory factors in 2.2% (17/788) of the fatal accident reports. Although qualitative methods are more typically designed to explain phenomena than to explore causal relationships, the goal of the inspectors’ inquiries was to gather all relevant information in order to reach conclusions with regard to the causes of a fatal event. The content analysis of 788 reports spanning a 16-year period argues strongly in favor of, although it cannot prove, a causal relationship between noise and fatal accidents in the 17 cases identified by the inspectors. Given the methodological limitations (i.e., access to written reports but not to inspectors’ notes, limited data in some reports, and review of fatal accident reports only) and inspectors’ constraints during investigations, this result (2.2%) most likely underestimates the proportion of workplace accidents explained at least partly by noise.

Interference with communication likely explains the causal relationship between noise and accidents. In all the 17 cases in which inspectors identified noise as a cause (15 involving a worker being struck by a moving vehicle), one aspect of communication was impaired. Indeed, the content analysis revealed that the warning device either failed or could not be heard over the ambient noise.

Interestingly, noise was identified as a cause in 11 cases during the 1990-1999 period, a time when inspectors were not, to the authors’ knowledge, specifically trained to carry out noise assessments and during which the causal relationship between noise and accidents was not yet well known or established. As inspectors gathered information from witnesses and other sources to understand the circumstances surrounding a fatal accident, the hypothesis of noise acting as an essential factor in cases where communication was at stake likely emerged intuitively. So did the interference with communication as a noise-related cause of accidents. In one case, the use of HPDs at the time the accident occurred was considered to have interfered with the recognition of the backup alarm and warning shouts. These observations reinforce the authors’ interpretation of these results.

Noise is typically not identified as the sole cause while explaining fatal events. Indeed, multiple causes were identified in most accident reports. For the 21 cases in which noise was analyzed directly as a potential cause, shortcomings in work methods and work organization were also identified in all but four reports (data not shown). Lack of adequate training, poor visibility, and faulty or absent safety measures were among the other identified modifiable causes, providing useful insight into the occurrence of fatal accidents within noisy work settings. Such factors could be considered potential confounders, along with other known factors such as age in epidemiological studies investigating the relationship between noise and workplace accidents.

Other known adverse effects of noise may also contribute to fatal accidents including reduced vigilance, precision, and visual span.[21] Since inspectors only include essential elements in their analysis to conclude on potential causes, noise is not identified as a cause in situations where these adverse effects come into play. This may partly explain why the impact of noise, measured in terms of relative risk or attributable fraction reported in some epidemiological studies,[8111619] is greater than the findings that the current study suggests.

In the current study, only fatal accident reports were reviewed. However, some epidemiological studies report an association between noise and nonfatal accidents.[81113141619] Given a causal relationship between noise and accidents, noise would likely contribute to a significantly greater number of accidents than these findings suggest if nonfatal injuries were also included.

Author consensus was achieved relative to the inspectors’ choice of noise measurements, analyses, and conclusions. Such a judgment was based solely on the information available in the written reports. Access to the full range of information gathered by the inspectors (including notes, simulations, and interviews) might have yielded a different judgment.

Inferences were often necessary to determine if the fatal accident had occurred in a noisy environment since most reports did not contain noise measurement data. Noise may affect communication at various levels as its effect consists of a complex interaction between different factors according to Hétu's[21] and Wilkins’[22] models. Nevertheless, a conservative approach was used in this study to define a noisy environment in order to minimize overestimation.

A rather conservative approach was also used by the authors in deciding that noise could have been mentioned in cases when it was not explicitly stated by the inspectors. This may partly explain the rather low percentage of such reports (3.9%) in the 2000-2005 subset. However, the authors judged that noise was considered as a potential cause by the inspectors in the vast majority of events in which it should have been.

The findings of this study suggest that noise should be systematically considered as a potential cause in all investigations of work-related accidents where vehicular movement or communication between workers is involved. As noise may also interfere with vigilance and other risk factors for accidents, it may be a much more important contributing factor to accidents than previously thought and than what is suggested by the findings of the current study. Given the omnipresence of noise and its plausible effects on worker safety, it should be a key component in the prevention of occupational accidents. In addition to reducing the risk of hearing loss, published results suggest that reducing workplace noise can yield beneficial effects on communication, worker comfort, and potentially, vigilance.[11124142434445464748] Further studies, particularly those exploring the contexts of impaired communication such as warning sound perception and interaction between noise and other risk factors for accidents, are needed to better understand the ways in which noise may cause or contribute to accidents as well as increase the effectiveness of accident prevention efforts.

Financial support and sponsorship

Public Health Department of Chaudière-Appalaches.

Conflicts of interest

There are no conflicts of interest.