Exposure Injuries & Diagnosis – What’s New?

Published Categorized as Compensation Café

Workers who are exposed to hazardous substances in the workplace often suffer serious, even fatal, injuries. Then why are exposure injuries such difficult compensation cases and why are so many exposed workers denied compensation?

Some exposures cause well known medical conditions (like asbestos & cancer).  However, other toxic exposures cause symptoms (respiratory distress, nausea, etc.) which elude a firm diagnosis. In the past, a lack of a firm diagnosis was a significant barrier to compensation and as many workers found out, this barrier had systemic roots. There is limited scientific research into toxic exposures and insufficient medical training about exposure injuries.   

Fortunately, in B.C., over the last decade, the legal role of a diagnosis in exposure cases was clarified in a number of court decisions. In 2020, the Board amended policy C4-25.10 RSMC II  to read as follows: 

Confirming the diagnosis of many occupational diseases may be difficult.  This is particularly so for the poisoning by some of the metals and compounds listed in Schedule 1, the symptoms of which may be similar to the symptoms caused by common complaints that produce fatigue, nausea, headache and the like. Evidence that an occupational disease has been diagnosed is relevant and will generally be given significant weight by the Board, but it is not a requirement under section 136(1) of the Act.

The question for the Board is whether it is “at least as likely as not” that the worker has or the deceased worker’s death was caused by, an occupational disease designated or recognized by the Board as an “occupational disease”. 

So what are the “building blocks” for a compensation case from toxic exposures for injuries which are difficult to diagnose?   

To what toxic substance was the worker exposed?

The first question in all exposure case is what toxin/s may be involved?   In some cases, this is obvious;  in many cases, it is not. 

Schedule 1 lists some specific toxins (e.g. lead, mercury, phosphorus), some general groups of toxins (e.g. organic solvents) and some chemical compositions that are toxic (Nitrous fumes or chemicals containing CN group).  There is also an “umbrella” category of “other toxic substances” and additional categories of symptoms or conditions, such as acute upper respiratory inflammation.  This list is only a start.   

The term “toxin” is more specifically identified in the WHIMIS 2015 system in which toxic chemicals are  identified, along with their chemical properties and safe handling and risk profiles.  Under OH & S regulation, the relevant WHIMIS 2015 information must be provided on  Material Safety Data Sheets (MSDS)  (and labels) for every product and process in every workplace.   Using these MSDS sheets, workers can identify what chemicals are involved in a potential exposure and the possible mechanism of exposure (inhalation, ingestion, absorption through skin, etc.) as well as the impact of some workplace conditions, such as temperature, storage, handling and combinations with other chemicals.  

Unfortunately, these MSDS sheets do not identify those toxic chemicals which arrive in the workplace from  external sources.  This can include historical contaminants  (mercury contamination from a previous enterprise), toxins arriving from outside the workplace (such as a nearby construction site), accidental mislabelling or mixing of chemicals or the unregulated release of toxins in a fire or accident. All of these can result in toxic exposures which are more difficult to identify or quantify.

When can an acute Exposure can be treated as a Personal Injury ?

A sudden and acute exposure can be deadly.  In 2017, three workers lost their lives in a catastrophic ammonia release at the Fernie Memorial Arena.  An undetected pinhole had developed in the refrigeration-system which allowed for the intermixing of brine and ammonia.  When the compromised refrigeration equipment was turned on, the workers were suddenly exposed to a lethal concentration of ammonia. Other acute exposures only create acute symptoms. 

It is helpful to know that when acute exposure symptoms (or death) are diagnosed as a recognized OD, they can be addressed as a personal injury that arises from an “Infectious Agent or Disease Exposure” (policy C3-12.30).  This simplifies many aspects of a compensation claim.

For example, an office worker was exposed to tar fumes when her office building was being tarred for a new roof.  On one day, the worker could smell strong tar fumes coming in through her office window. At first, the fumes did not bother her but about four hours into her shift she began to experience symptoms of chest and throat tightness, difficulty breathing, burning eyes, body aches and a headache.   The symptoms resolved after she left work but returned when she went back to work. Her doctor diagnosed her with acute exposure to noxious fumes based on her symptoms, the patterns and It timing of their occurrence and resolution and the material safety data sheets (MSDS) for coal tar pitch. WCAT accepted the worker’s condition as a personal injury under policy 12.30.  

An aggravation of a pre-existing disease by a specific incident can also qualify as a personal injury. 

It is also helpful to know that the top 5 chemicals resulting in acute work injuries have been identified as carbon monoxide, ammonia, chlorine, hydrochloric acid and sulfuric acid.   For all of these toxins, an acute exposure can be addressed as a personal injury with an OD diagnosis. 

What if the worker has symptoms after an exposure but no firm diagnosis?

Of course, many exposure injuries do not result in a firm OD diagnosis and policy #25.10 was amended to state both that a firm diagnosis of an OD is not necessary and that the Board may decide a diagnosis on “as likely as not” basis. The importance of this amendment was felt immediately.  

In one case, an electronic technician was working in a closed garage when he heard an engine revving, filling the garage with diesel exhaust. The worker began coughing severely and experienced difficulty breathing and shortness of breath (dyspnea), a condition which did not improve over time. His claim was denied at the Board and by the Review Division because he had not been diagnosed with an occupational disease. On appeal, a WCAT panel accepted the worker’s claim, citing the new policy #25.10. The panel concluded that since the worker’s symptoms and his exposure to a high level of gasoline fumes satisfied the requirements of Schedule 1, Item 9, his claim for an acute exposure to gasoline fumes should be accepted.

Of course, problems will arise if the Board’s “accepted diagnosis” is incorrect or at odds with the exposure evidence. In a recent case, a bus driver became ill after driving a bus filled with gasoline fumes. The Board treated this as a case of carbon monoxide poisoning and denied his claim.  However, since there was little evidence that the worker was actually exposed to carbon monoxide,  a Review Division Medical Advisor opined that gasoline fumes (rather than carbon monoxide) caused his symptoms. At WCAT, the panel addressed both conditions – carbon monoxide poisoning and inhalation of gas fumes – and dismissed the carbon monoxide claim. 

The panel noted that gasoline contains benzene and may also contain n-hexane, xylene and toluene – all of which are “organic solvents”.  The worker’s condition was then characterized as “poisoning by organic solvents” (Item #1(7)) or alternatively “poisoning by other toxic substances.” (Item #1(13)). Given the worker’s medical symptoms and the RDMA opinion, the panel found that it was “as likely as not” that the worker had one of these recognized ODs  and that since he clearly had an “exposure”, the presumption applied and his claim was accepted.     

The causation test – “causative significance”

Even with a firm OD diagnosis, there is still the issue of causation – did the worker’s occupational exposures cause that disease?  This is particularly difficult where the worker is exposed to multiple chemicals over many years. A successful case often depends on both good exposure evidence and good medical evidence. This is seen in WCAT A2101587 (January 28, 2022) where the panel accepted the worker’s claim for asthma and COPD, after years working in a pulp mill.   

Another approach is called “Cluster Advocacy”, now promoted by the Occupational Disease Reform Alliance of Ontario. Using this approach, advocates will seek compensation for “clusters” of injured workers who have all had the same exposures to the same toxins.  One of their cases involved the workers in “Chemical Valley” in Sarnia Ontario.  Another case involved hundreds of construction workers who were required to work on a renovation project at a paper mill, while the mill continued to operate.  Extensive fumes engulfed the construction workers in a “chemical soup” including carbon monoxide and hydrogen sulphide.  Many workers were affected immediately, going to the hospital, and in the years since, have developed complex health issues.  Until now, few of these cases have been accepted by compensation but the work is ongoing.  This “cluster advocacy” approach was also used by 3 health care unions in B.C., to win acceptance of a group of cancer cases in the British Columbia (Workers’ compensation Appeal Tribunal vs. Fraser Health Authority 2016 SCC 25.  


Toxic exposure cases are important.  Workers with exposure injuries, like other injured workers, need and deserve compensation.  But their exposure cases also highlight the toxic dangers that can lurk in  workplaces and serve as real-life warnings about areas of unsafe work.   

(1) The International Labour Organization (ILO) now estimates that worldwide, 6 people dies from occupational disease (OD) for every person who dies from trauma at work.  The vast majority of OD deaths are caused by toxic occupational exposures. 

(2) In Using Scientific Evidence and Principles to Help determine the Work-Relatedness of Cancer:  Final Report, Occupational Cancer Research Centre (January 9, 2020), it was a key finding that Canadian medical students receive very little basic training in occupational health and that there are very few occupational medicine specialists.  If this is true for occupational cancer, it is even more critical for other types of exposure injuries. 

(3) In 2015, the Federal government amended the Hazardous Products Act,  to incorporate the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)  into its Workplace Hazardous Materials Information System (now WHIMIS 2015).   

(4) Two helpful resources are the National Institute for Occupational Safety & Health (NIOSH) and the Centre for Disease Control and Prevention (CDC) in the U.S.  Both organizations have on-line publications, research and analytics about particular toxins or hazardous substances, products and occupational activities.  

(5) WCAT # A2002164

(6) In decision # A2200562 (Nov 14, 2022), WCAT accepted the worker’s claim for an aggravation of a worker’s pre-existing respiratory condition due to workplace scents on a particular day. 

(7) Centre for Disease Control and Prevention “Top Five Chemicals Resulting in Injuries from acute Chemical Incidents  in Nine States, 1999-2008 (Surveillance Summaries, April 10, 2015/64 (SS02); 39-46) .  NOTE:  These top 5 chemicals involved in acute exposures are different than the top 4 carcinogens identified as being responsible for the greatest occupational cancer burden in Canada – asbestos, diesel engine exhaust, solar radiation and crystalline silica. See Using Scientific Evidence and Principles to Help determine the Work-Relatedness of Cancer:  Final Report, Occupational Cancer Research Centre (January 9, 2020).

(8) WCAT #  A1902600 (June 26, 2020)

(9) Schedule 1 not only does not require a diagnosis for all items, but it also sets what level of exposure is required.  For some items, it is simply “exposure”.  As noted in a BCCA case, the first step is to determine whether this specific exposure level is met and “..it is improper to consider whether the exposure was sufficient to cause the disease.”  That is to be considered only after the presumption is applied.

(10) WCAT A2201773 (February 27,2023)

(11) https://ofl.ca/advocacy-groups-odra 

Originally published on the Worker Education website by former WELLS Director Janet Patterson.