The Appeal CommissionThe Workers Compensation Act of Manitoba

Applicable Legislation and Policy

The Appeal Commission and this panel are bound by the Act, regulations and policies of the WCB’s Board of Directors.

The employer is appealing the acceptance of the worker’s claim for a lung condition which has been diagnosed as a form of lung cancer. Subsections 1(1), 4(1) and 4(4) of the Act are applicable.

Subsection 1(1) of the Act defines accident to include an occupational disease and defines occupational disease as:

"occupational disease" means a disease arising out of and in the course of employment and resulting from causes and conditions

(a) peculiar to or characteristic of a particular trade or occupation; or

(b) peculiar to the particular employment;

but does not include

(c) an ordinary disease of life; and …

Subsection 4(1) of the Act provides that where a worker suffers personal injury in a workplace accident, compensation is payable.

Subsection 4(4) of the Act deals with cause of an occupational disease and provides:

Cause of occupational disease

4(4) Where an injury consists of an occupational disease that is, in the opinion of the board, due in part to the employment of the worker and in part to a cause or causes other than the employment, the board may determine that the injury is the result of an accident arising out of and in the course of employment only where, in its opinion, the employment is the dominant cause of the occupational disease.

To assist with the adjudication of claims involving disease, the WCB’s Board of Directors made WCB Policy 44.20, Disease/General. It provides guidance on determining the dominant cause of a disease where there is more than one cause.

Employer’s Position

The employer was represented by legal counsel and a staff person. The employer’s health and safety superintendent (“superintendent”) and a technical assistant also attended the hearing.

In support of the employer’s position, legal counsel asked that a video and pictures of the mine site be admitted into evidence at the hearing to show the panel the work areas in the mine. The material had not been provided within the time period allowed by regulation but was admitted with the worker’s agreement.

The superintendent and other staff commented on the contents of the video. The worker also commented on the video. The superintendent noted that the video was taken in October 2007. Legal counsel acknowledged that the conditions in the video are not identical to the conditions that the worker worked in, but would be helpful in assisting the panel in visualizing the work environment of the mine.

Legal counsel addressed the reason for the employer’s appeal. He submitted that the MRP that was convened on this claim erred in weighing the evidence of the WCB medical consultant and the occupational health physician. He stated that the MRP had a mistaken belief that once a smoker stops smoking, with the passage of time, it eventually becomes a non-factor as a risk in contracting lung cancer. Legal counsel submitted that the dominant cause of the worker’s lung cancer was in fact his prior smoking history and not the workplace.

An epidemiologist was called by the employer as a witness at the hearing to provide evidence on the probable cause of the worker’s lung cancer. In support of his oral evidence, the epidemiologist also provided a written report and opinion prior to the hearing.

The epidemiologist identified the facts that he considered in preparing his report and reaching his conclusion regarding the dominant cause of the worker’s lung cancer. The work history and facts he considered included:

· the worker smoked one pack of cigarettes daily for approximately 13 years from 1964 to 1976/77.

· the worker worked as a mechanic from 1967 to 1979 for other employers in environments where he was exposed to asbestos.

· the worker worked for the accident employer from 1981 to 1993 as a diesel mechanic and as a supervisor (underground), where he was exposed to diesel exhaust, asbestos and mine dust.

· the worker worked in a zinc plant for the accident employer from 1993 to 2002 where he was exposed to second hand tobacco smoke from co-workers and other chemicals.

· the worker was diagnosed with lung cancer in 2002.

The epidemiologist provided a general explanation regarding the field of epidemiology, the use of studies of large populations in the assessment of occupational diseases, and the standards generally used in determining cause and effect. He indicated that the purpose of the epidemiologic studies is to compare disease rates between populations with and without particular exposures or risk factors, and to compare the relative risk between those compensable groups. He provided considerable information on what qualifies (from an epidemiologist’s perspective) as a “significant” relative risk, taking into account as well a 95% confidence interval, to exclude results due to chance. He cited a major text (Monson, R.R., Occupational Epidemiology, 2^nd Edition) which defined relative risks as follows: 1.0-1.2 None, 1.2-1.5 Weak, 1.5-3.0 Moderate and 3.0-10.0 Strong.

He referred to a number of epidemiological studies. He compared the relative risk of exposure to various substances considered to be present in the workplace to the relative risk of smokers and former smokers. He found the relative risk (expressed as a ratio) for former smokers was statistically significant compared to the relative risk of any other exposure. He concluded that based on a comprehensive review of these epidemiologic studies pertinent to the worker’s occupation and lifestyle exposures:

· the worker’s lung cancer was not caused by his potential exposures to brake dust, diesel exhaust or mine dust (including silica) while he was employed by the employer.

· the worker’s lung cancer was not caused by his potential exposure to second-hand smoke (environmental tobacco smoke or passive smoking) either at home or at work

· the dominant cause of the worker’s lung cancer was the worker’s prior history of cigarette smoking.

The epidemiologist provided a report subsequent to the oral hearing, in response to the report of the occupational health physician dated June 12, 2008. The epidemiologist confirmed that in considering “dominant cause” he used the WCB’s administrative guidelines which provided that for workplace exposures to be the dominant cause it is necessary that the combined effects of occupational causes exceed the combined effects of non-occupational causes. The epidemiologist disagreed with the opinion of the occupational health physician which he interpreted as erroneously concluding that the worker’s history of cigarette smoking actually reduced the worker’s lung cancer risk by 58%. He said that the occupational health physician had misused and misinterpreted the results of a study dealing with the effects of smoking and that his conclusion is simply wrong. He asserted that the risk ratio for “former smokers” over “never smokers” would be 3.3 which is statistically significant and exceeds all other possible identified risks.

Worker’s Position

The worker was represented by a worker advisor who made a presentation on behalf of the worker. The worker answered questions regarding his claim.

The worker’s representative noted that an occupational health physician and MRP concluded that the worker’s condition was caused by exposure in the workplace. According to the MRP, this included exposure to diesel exhaust and mining dust with various toxic components over many years. He noted that the MRP found that the worker’s remote history of cigarette smoking or that of his wife’s smoking played little or no role in causation of his cancer. He also noted that the MRP’s recommendation was unanimous. The representative submitted that in accordance with WCB policy 44.40.10, the worker has medical evidence of disability arising from his work.

The worker’s representative noted that the worker has an extensive history of working in confined spaces underground while employed as a mechanic repairing heavy duty diesel equipment. He advised that the worker’s duties included welding which on average in a given week would be five hours. He stated there was no ventilation to draw away the fumes from the welder. The representative also advised that the worker was exposed to second hand smoke in the workplace.

The worker’s representative asked the worker about his employment duties and the work conditions. The worker confirmed that fumes were present in the workplace and that co-workers smoked in the workplace. He also described the ventilation system in the mine during the period that he worked underground.

The worker’s representative commented that it was unfortunate the epidemiologist called as a witness by the employer did not have an opportunity to look at the worker’s job description. He referred to literature dealing with the composition of welding fumes and the effects of diesel fumes in support of the position that the worker’s lung cancer was caused by exposure to these fumes.

The worker advised that he lives about ten miles from the mine and has not smoked in 26 years. He also advised that his wife does not smoke and that smoking is not permitted in their home. He said he is not subjected to pollutants away from work.

After the adjournment of the oral hearing, the worker was provided with an opportunity to make a final written submission. The worker’s submission included a copy of an additional medical report from the occupational health physician dated June 12, 2008. The physician disagreed with the conclusion of the epidemiologist. The physician noted that scientific literature supports an association between occupational exposure to diesel exhaust and lung cancer. He concluded that the exposure to diesel exhaust would be the most significant factor in relation to the development of the worker’s lung cancer.

In reference to a study relied upon by the epidemiologist the occupational health physician wrote that:

“I feel that using the general population comparison would be better to understand your risk as this group is closer to the comparison groups in the occupational studies. Hrubec and McLaughlin’s work (3) provided an SMR of 42 for lung cancer mortality for people who had smoked 10-20 cigarettes per year who had stopped smoking for 20-29 years, suggesting that the risk in this group has 42% of the risk of the general population. Since people who have your smoking history have roughly 40% the risk of developing lung cancer compared to the general population and workers who had exposure to diesel exhaust have between 1.33 to 1.47 of the risk of developing lung cancer, the risk from diesel exhaust exposure would be more than double your baseline risk of lung cancer. This argues that diesel exposure would be the dominant cause of your lung cancer.”

Analysis

The employer is appealing the acceptance of the worker’s claim. For the employer’s appeal to be successful, the panel must find on a balance of probabilities that the worker’s lung condition is not a personal injury by accident arising out of and in the course of employment, or in other words, is not causally related to his employment. In this case the worker’s lung condition is a disease and not the result of a specific incident. Further the etiology of the disease is known to be multi factorial, or, in other words, may be caused by both workplace and non-workplace exposures.

In addressing this issue, the panel must determine whether the worker’s lung condition is an occupational disease and whether the worker’s employment (workplace exposure) is the dominant cause of the lung condition. WCB Policy 44.20 provides that in determining the dominant cause, the panel, must consider whether the combined effect of the employment causes exceeds the combined effect of the non-employment causes. Only where the employment causes exceed non-employment causes is the claim acceptable as an accident arising out of and in the course of employment.

The panel acknowledges that lung conditions, such as the worker’s lung cancer, can be caused by occupational exposures and can be occupational diseases. Accordingly, the panel has considered the worker’s lung condition under subsection 4(4) of the Act and concluded, on a balance of probabilities and considering the record as whole, that the dominant cause of the worker’s lung condition was the worker’s prior history of smoking and not the worker’s employment. The panel finds that the worker’s lung condition does not meet the definition of accident and his claim is therefore not acceptable.

Findings of Fact

The major facts underlying this case include:

· the worker smoked approximately one pack of cigarettes per day from 1964 to 1976/77.

· he resided with his wife who also smoked approximately one pack per day for 8 to 9 years until she stopped approximately 3 years after he did.

· he worked for approximately 3 years as a truck driver and a mechanic where he may have been exposed to asbestos from brake repairs.

· he commenced working for the employer in 1980-1981 and worked underground until approximately 1993 and then worked in a zinc plant until approximately 2002.

· the worker was subjected to second hand smoke while in the employ of the accident employer but this exposure was not continuous and primarily took place in a nearby lunchroom.

· the worker was subjected to diesel fumes, mine dust and other contaminants while employed with the employer.

· the worker’s duties included small amounts of welding.

Scientific Evidence

There is no direct evidence on the file dealing with the relationship between the worker’s lung cancer and his workplace. Cases such as this, involving disease, rarely have the benefit of clear scientific evidence that can demonstrate a direct biological linkage between a specific exposure and the later development or onset of the disease.

Instead, in the case of occupational disease, a review of epidemiological studies – the study of large populations – are used to determine if certain diseases are more prevalent for certain types of workers, and thus the basis for the acceptance of the disease in a particular claim, as an “accident” under the Act. In this process, large scale studies are done of workers in certain types of industrial or workplace settings to assess whether certain medical conditions are more likely to occur at those workplaces than in the general population. These studies look for statistically significant increases in the morbidity/mortality of workers in certain workplaces or occupations for certain diseases, in comparison to a control group which is usually drawn from the general population. The studies then employ comparisons of relative risk expressed as “standardized mortality ratios” and “odds ratios”. A large risk ratio means a strong association which is more likely to be causal.

In cases such as this one, where a particular type of cancer is claimed to be related to an occupational exposure, specialists (and ultimately, the panel) will assess the epidemiological studies to determine if there is a causal relationship between the particular cancer and the workplace. As noted in the evidence provided by the epidemiologist witness (and accepted by the panel as consistent with the general standards used in epidemiology and in the consideration of occupational diseases), the studies must deal with comparable populations (those exposed and not exposed), and must ultimately demonstrate a statistically significant relative risk, for there to be a causal relationship between the disease and the workplace.

Where there is a sufficient body of scientific evidence to establish a causal relationship between a particular disease and sufficient exposures in certain occupations, it is open to the WCB or this panel to determine, on a balance of probabilities, that there is a “preponderance of scientific evidence” - in other words, a balance of probabilities - to establish that the worker’s cancer was caused by his workplace.

The parties relied at the hearing upon scientific evidence, assessed and interpreted by medical experts, to support their positions. The worker relies upon the opinion of the occupational health physician outlined in reports dated December 19, 2003 and June 12, 2008, the opinion of the MRP and certain literature dealing with exposure to fumes. The occupational health physician opined that the worker’s lung cancer was likely caused by the worker’s exposure to diesel exhaust. The employer relies upon the opinion of the WCB internal medicine consultant and the epidemiologist who found that the worker’s lung cancer was likely caused by the worker’s prior smoking history.

The Dominant Cause

The panel has considered the above opinions and other information on the claim file and has concluded, on a balance of probabilities, that the dominant cause of the worker’s lung cancer is his prior cigarette smoking. In reaching this decision, the panel places significant weight upon the opinion of the WCB internal medicine consultant and the epidemiologist.

The WCB internal medicine consultant offered the opinion that the primary cause of the worker’s lung cancer was related to cigarette smoking and disagreed that diesel exhaust had proven to be carcinogenic in humans.

The epidemiologist provided a lengthy opinion dated October 8, 2007 oral evidence at the hearing, and a response to the occupational health physician dated July 31, 2008.

In the October 2007 report, the epidemiologist considered the relative risk of exposure to several substances. Specifically, he considered the worker’s potential exposures, studies of mechanics exposed to asbestos fibres generated from brakes, studies of mechanical maintenance workers exposed to diesel exhaust, studies of mine dust containing silica, and studies of active and passive cigarette smoking. He stated that:

“In conclusion, based upon my own research as well as a critical review and analysis of pertinent studies by other investigators, there is no epidemiological evidence indicating that vehicle mechanics exposed to asbestos fibers from brake repairs, or diesel mechanics exposed to diesel exhaust are at any increased risk of lung cancer. Furthermore, [the worker’s] indirect exposure to mine dust containing silica was not the dominant cause of lung cancer. Similarly, there is no epidemiologic evidence indicating that exposure to environmental tobacco smoke at work is a significant causal factor for lung cancer. Therefore, [the worker’s] lung cancer could not have been the result of his employment as a diesel mechanic. On the other hand, there is overwhelming evidence that [the worker’s] own smoking history was a significant and strong causal factor of his lung cancer. Therefore, I conclude that [the worker’s] own smoking history was the “dominant cause” of his lung cancer.”