Page 1  
Decision No.: 2022-0288  
Appeals Commission for Alberta Workers’ Compensation  
Docket No.: AC0139-20-54  
Decision No.: 2022-0288  
Introduction  
[1]  
This appeal considers whether the worker has an acceptable Workers’  
Compensation Board (WCB) claim for systemic mastocytosis, a rare condition  
involving the pathological build-up of certain blood cells, called mast cells, in the  
body.  
Background  
[2]  
[3]  
[4]  
The worker is an engineer, with an occupational history of benzene and toluene  
exposure.  
He was diagnosed with systemic mastocytosis in March 2017. This condition  
subsequently progressed in severity from smoldering to aggressive.  
The worker filed a WCB claim in October 2018. The WCB case manager denied  
his claim on January 23, 2019, and again on January 6, 2020 on the basis that  
the worker’s occupational exposures did not cause or materially contribute to his  
condition.  
[5]  
[6]  
The WCB’s Dispute Resolution and Decision Review Body (DRDRB) confirmed  
the case manager’s decision on April 1, 2020.  
The worker now appeals to the Appeals Commission.  
Summary of Decision  
[7]  
[8]  
[9]  
We find that the worker has an acceptable WCB claim for his systemic  
mastocytosis.  
The evidence shows the worker was exposed to benzene and toluene during his  
employment.  
We find it appropriate in the circumstances to apply the ‘but for’ test for causation  
to determine whether these occupational exposures caused the worker’s  
condition. As the worker’s claim does not involve poisoning from benzene and  
toluene, the causal presumptions in the legislation do not apply. Further, the  
material contribution test is inapplicable as there are no epidemiological studies  
addressing this rare condition.  
Classification: Protected A  
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Decision No.: 2022-0288  
[10]  
[11]  
Accordingly, we considered whether the evidence, on a balance of probabilities,  
shows that but for the worker’s occupational exposures the worker would not  
developed mastocytosis.  
We conclude that this test has been met. The medical evidence established a  
causal connection that is more than speculative, and is based upon the medical  
knowledge of the worker’s two treating specialists. While there is no research  
related to the worker’s rare condition specifically, we accept the medical  
professionals’ opinions that the established causal association between benzene  
exposure and other blood disorders is applicable by analogy. This supports a  
causal connection between the worker’s occupational exposures and his  
condition. Further, the medical evidence before us indicates that occupational  
exposures are the most likely cause of the worker’s mastocytosis; no other  
probable cause is identified.  
Issue  
[12]  
Does the worker have an acceptable claim for systemic mastocytosis?  
Analysis  
Legislation and Policy  
[13]  
[14]  
Excerpts of the relevant legislation and policies are in the appendices.  
We are bound by the Workers’ Compensation Act, RSA 2000, c W-15 (WCA)  
and the WCB policies when making our decision (section 13.2(6)(b)).  
[15]  
The WCA states that compensation is payable to a worker who suffers personal  
injury caused by an “accident” (section 24(1)(a)). An “accident” is an unexpected  
mishap that arises out of and occurs in the course of employment (WCA, section  
1(1)(a)). An accident arises out of employment when it is caused by an  
employment hazard. It occurs in the course of employment when it happens at a  
time and place consistent with the obligations and expectations of employment.  
[16]  
[17]  
In order to be compensable, an injury must have been caused by the accident.  
A number of factors are included in the causation analysis, including the worker’s  
medical diagnosis, work factors and personal factors (Policy 02-01 Part II,  
Application 7).  
The legal test for causation is the “but for” test, meaning that, but for the work  
exposures, the injury would not have occurred (Policy 02-01, Part II, Application  
7). Work does not have to be the only factor, or even the primary factor, but  
must have been a necessary cause of the injury.  
Classification: Protected A  
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Decision No.: 2022-0288  
[18]  
Causation is a factual analysis, based upon the evidence and accepted medical  
knowledge, not on a speculative connection. It is proven on a balance of  
probabilities, or more likely than not (Policy 02-01 Part II, Application 7).  
[19]  
[20]  
There are some circumstances in which a different standard of causation may  
apply.  
For instance, certain occupational diseases that occur in certain industries are  
deemed to have been caused by working in that industry (see WCA, 24(6),  
Workers’ Compensation Regulation, AR 325/2002 (the Regulation), section 20  
and Schedule B). For example, this presumption applies to workers in industries  
where there is significant occupational exposure to organic solvents (including  
benzene and toluene) who have experienced poisoning (see Schedule B,  
Column 1, 1(g)).  
[21]  
Another example is where a disease (such as cancer) has multiple risk factors  
and it is impossible to determine the actual cause (Policy 02-01, Part II,  
Application 7). In these circumstances, since exact causation cannot be  
determined, WCB will consider whether work factors materially contributed to the  
risk that the individual would develop the disease. This is determined through  
epidemiological evidence regarding the relative risk that the occupational  
exposure was the cause of the particular disease (Policy 02-01 Part II,  
Application 7). WCB policy states that a relative risk of 2.0 or higher will satisfy  
the material contribution test.  
Key Submissions  
[22]  
[23]  
The worker’s representative submits that the worker has an acceptable WCB  
claim. His occupational exposure to known carcinogens, including benzene, is  
well known and the evidence supports a causal link between this exposure and  
his condition.  
The representative first argues that the worker’s systemic mastocytosis is an  
occupational disease within the meaning of the WCA and the Regulation. There  
is no evidence rebutting the presumption that the worker’s condition was caused  
by work.  
[24]  
[25]  
In the alternative, the representative submits that the evidence establishes the  
worker’s condition was work-related.  
The representative acknowledges that there is no available epidemiological  
evidence available regarding the risk of developing systemic mastocytosis from  
occupational exposure to benzene or toluene.  
Classification: Protected A  
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Decision No.: 2022-0288  
[26]  
[27]  
[28]  
Given this, she submits that the causation test to apply is the standard “but for”  
test. She argues that opinions from the worker’s two specialists – his  
hematologist and occupational medicine specialist - satisfy this test, establishing  
the causal connection between the worker’s condition and his occupational  
exposure to benzene and toluene.  
We are urged to place the greatest weight upon the worker’s treating  
occupational medicine specialist. This physician spent hours assessing the  
worker, and noted that, while there is no epidemiological data, benzene exposure  
does cause similar blood conditions and there is no other clearly identifiable  
etiology of the worker’s systemic mastocytosis.  
The representative argues that the panel should place less weight upon the  
conclusions of the WCB medical consultant, also an occupational medicine  
specialist. She states that the medical consultant’s research establishes that  
there is no epidemiological evidence regarding the worker’s condition. However,  
she disputes the medical consultant’s conclusion that the lack of research on this  
rare condition renders it “highly unlikely” that the condition was caused by the  
worker’s exposures.  
[29]  
At the hearing, the worker explained that his condition is very rare, with only two  
people in his home province with the condition. He understood that this was the  
reason that no epidemiological studies are available. He explained that his  
condition is currently managed with treatment, and that stem cell transplants  
have been considered.  
Questions to be Answered  
[30]  
In order to decide this appeal, we must answer the following questions:  
[30.1]  
Is the worker’s systemic mastocytosis an occupational disease within the  
meaning of the WCA and the Regulation, such that is presumed to have  
been caused by work?  
[30.2]  
If not, does the evidence before us show that the worker’s systemic  
mastocytosis was caused by work?  
Findings and Reasons  
1. Is the worker’s systemic mastocytosis an occupational disease to which the  
presumptions apply?  
[31]  
We acknowledge that the worker’s claim is founded in his occupational exposure  
to benzene and toluene, however the presumptions in the WCA and the  
Regulation do not apply.  
Classification: Protected A  
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Decision No.: 2022-0288  
[32]  
[33]  
[34]  
[35]  
The evidence before us shows that the worker experienced occupational  
exposure to benzene and toluene during his career. The WCB medical  
consultant described these as “high-level benzene exposures”. His occupational  
medicine specialist described them as “substantial”.  
The worker reported performing quality control and being in contact with those  
fluids at times without wearing breathing equipment. He also reported occasional  
hydrocarbon splashes onto his unprotected skin while working with samples,  
described as once per week for about a year.  
The evidence does not, however, indicate that the worker suffered poisoning  
from these substances, which is required by Schedule B of the Regulations for  
the presumptions in the WCA to apply. Rather, the worker’s claim is for a  
different condition: systemic mastocytosis.  
As the statutory presumptions do not apply to the worker’s claim, we now turn to  
consider whether the evidence supports a causal connection between the  
worker’s occupational exposures and his systemic mastocytosis.  
2. Was the worker’s systemic mastocytosis caused by work?  
[36]  
[37]  
To answer this question we must first consider the appropriate test for causation.  
The WCB medical consultant has provided a detailed explanation of  
mastocytosis in his January 16, 2019 opinion.  
[38]  
Mastocytosis is a myeloproliferative disorder, involving the excessive  
accumulation of mast cells (a type of blood cell) in one or more tissues. There  
are two classes; cutaneous mastocytosis, which is limited to the skin, and  
systemic mastocytosis, which occurs in multiple organs. Mast cells are involved  
in the body’s immune response, and normally function by releasing chemicals to  
generate inflammatory responses. These chemicals (called mast cell-mediators)  
include histamine, prostaglandins and cytokines. Signs and symptoms  
associated with mastocytosis are similar to allergic and anaphylactic reactions.  
[39]  
[40]  
It is unclear to us whether the worker’s condition is cancerous; the WCB case  
manager refers to it as blood cancer, yet the worker’s treating specialists and the  
WCB medical consultant do not. In any event, mastocytosis involves a similar  
pathological accumulation of cells in the body.  
According to policy, the “material contribution” test is applied to diseases (such  
as cancers) in which it is impossible to determine the actual cause (Policy 02-01  
Part II). That is, WCB considers the available epidemiological evidence  
regarding the relative risk that work factors would have caused the disease.  
Classification: Protected A  
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Decision No.: 2022-0288  
[41]  
[42]  
There is no available epidemiological evidence regarding risk factors contributing  
to the development of mastocytosis. This is acknowledged by the worker’s  
hematologist, his occupational medicine specialist, and the WCB medical  
consultant (also an occupational medicine specialist).  
We understand from the evidence that the lack of epidemiological data is  
because mastocytosis is a rare disorder. At the hearing, the worker explained  
that less than a handful of people have the condition in his province. The  
medical opinions in evidence confirm this:  
[42.1]  
In his January 16, 2019 opinion, the WCB medical consultant explains that  
mastocytosis is rare and the exact incidence is unknown. The report  
shows that the medical consultant performed extensive searches through  
multiple databases and textbooks and concluded that there is no literature  
associating mastocytosis to:  
Work (on a causation or aggravation basis),  
The construction and petroleum industries,  
Hydrocarbon and petrochemical exposure,  
Benzene and toluene exposure (separate or as a mixture).  
[42.2]  
In his December 14, 2018 opinion, the worker’s occupational medicine  
specialist describes his search for similar publications. He notes that  
there “. . . is no dependable body of literature describing the risk of  
mastocytosis . . . that would allow me estimate the likelihood of  
occupational causation more precisely.”  
[42.3]  
The worker’s hematologist’s August 7, 2019 opinion also acknowledges  
the paucity of data on the subject, noting she was not aware of any  
epidemiological data looking at benzene and toluene exposure and the  
development of systemic mastocytosis.  
[43]  
In the absence of epidemiological data, we find it appropriate to apply the general  
“but for” test of causation to the worker’s claim. That is, we must consider  
whether the evidence shows, on a balance of probabilities, that but for the  
worker’s occupational exposures, the worker would not have developed systemic  
mastocytosis.  
[44]  
We acknowledge that the medical opinions in evidence are unable to definitively  
conclude that the worker’s condition was caused by work, given the nature of the  
disease and the lack of epidemiological data. However, we also note that the  
Classification: Protected A  
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Decision No.: 2022-0288  
standards of medical causation and legal causation differ (see British Columbia  
(Workers’ Compensation Appeal Tribunal) v Fraser Health Authority, 2016 SCC  
25). This difference was explained in Alberta (Workers’ Compensation Board) v  
Alberta (Appeals Commission for Alberta Workers’ Compensation), 2010 ABQB  
368 at paragraph 87:  
“. . . At law, causation need not be determined with precision, but meet  
the appropriate burden of proof. Policy 01-03, Part 1 provides that a  
worker need only prove their claim on a balance of probabilities, and if the  
evidence for and against a decision is equally balanced, the issue will be  
resolved in the worker’s favour. On the other hand, scientific analysis of  
causation seeks a far higher degree of certainty to establish causation.”  
[45]  
We conclude that causation has been made out in the circumstances:  
[45.1]  
The worker experienced significant occupational exposures to benzene  
and toluene.  
[45.2]  
The absence of medical literature associating systemic mastocytosis with  
occupational exposures is explained by the condition’s rarity. Accordingly,  
we do not find that the lack of research means there is no causal  
association.  
[45.3]  
[45.4]  
The medical opinion evidence before us indicates that medical research  
associates benzene and toluene exposures to similar blood disorders and  
that such research can be applied by analogy.  
Not only is there no other cause or potential cause identified in the  
evidence, the medical opinion evidence describes the worker’s  
occupational exposure as the most likely cause.  
The worker’s occupational exposure  
[46]  
The worker’s occupational exposures to benzene and toluene throughout his  
career are described above. They are described as “high-level” and “substantial”  
by the WCB medical consultant and the worker’s occupational medicine  
specialist.  
The medical literature associating mastocytosis with occupational exposures  
[47]  
The evidence contains the details of the WCB medical consultant’s extensive  
search for medical literature causally associating the various forms of  
mastocytosis with work, benzene, toluene, and various industries which use the  
chemicals. The search yielded nothing. On this basis, the medical consultant  
concludes that systemic mastocytosis is neither linked to nor associated with  
benzene, occupations using benzene or as an occupational condition generally.  
Classification: Protected A  
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Decision No.: 2022-0288  
He further concludes that it is highly likely that the worker’s condition is  
non-occupational.  
[48]  
We are unable to reach the same conclusion. We do not find that the absence of  
medical literature is proof that there is no causal association. We find it  
significant that the lack of medical literature is explained by the acknowledged  
rarity of the worker’s condition. We also note that the same searches did not  
uncover literature disproving such a connection.  
The medical literature related to similar conditions  
[49]  
[50]  
We are persuaded by the opinions of the worker’s occupational medicine  
specialist and hematologist that the causal association between benzene  
exposure and other blood cancers apply to the worker’s condition by analogy.  
Accordingly, while such a causal association can not be epidemiologically  
quantified, it is medically supported.  
In his December 14, 2018 report, the worker’s occupational medicine specialist  
explains:  
“. . . [The worker] has been exposed to carcinogens; in particular  
benzene, which is capable of causing a number of hematological and  
lymphatic malignancies, based on a presumed effect at the stem cell  
level. . .”  
[51]  
The worker’s hematologist agrees:  
“. . . As benzene is a known carcinogen associated with other  
haematological malignancies, it would be appropriate to consider  
research regarding benzene and toluene exposure and myeloproliferative  
disorders and mastocytosis.”  
[52]  
[53]  
[54]  
She further refers to an International Agency for Research on Cancer (IARC)  
study, as well as statements from the IARC, the National Toxicology Program  
and the US Environmental Protection Agency’s Integrated Risk Information  
System. She notes each of these sources classifies benzene as a known  
carcinogen.  
We acknowledge that the WCB medical consultant disagrees, providing the  
opinion that the mechanisms underlying different blood diseases vary and noting  
that benzene exposure has a leukemogenic effect not a mastocytogenic one.  
Thus, research associating benzene to other blood disorders should not be  
applied in cases of mastocytosis.  
In his November 19, 2019 opinion, the WCB medical consultant reviews the  
research relating to the leukemogenic effect of benzene. He relies heavily upon  
research published in 2012. The medical consultant describes what is known  
Classification: Protected A  
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Decision No.: 2022-0288  
about benzene metabolization, noting that the variety and complexity of  
subsequent metabolites has rendered it difficult to determine which is most toxic.  
We understand from this description that the effect of benzene is complicated  
and multi stage.  
[55]  
The WCB medical consultant then describes what is known about bone marrow,  
and hematopoietic stem cells and their progeny. He states that whether or not  
cancers arise from stem cells is still under debate. What is known is that these  
stem cells differentiate into two categories of cells; lymphoid and myeloid. The  
research associates benzene exposure to blood disorders of cells in the  
lymphoid lineage not the myeloid lineage. Since mast cells are in the myeloid  
lineage, such research is not applicable.  
[56]  
[57]  
We place less weight upon this opinion, as the worker’s occupational medicine  
specialist addresses the medical consultant’s concerns and refers to more recent  
research.  
The worker’s occupational medicine specialist documented his response in his  
December 10, 2019 opinion. He cites more recent research supporting the  
proposition that benzene exposure is responsible for hematopoietic malignancies  
more widely (including cells in the myeloid lineage). The physician cites a 2018  
IARC article, an article from The Lancet Oncology and a 2019 study considering  
benzene exposure and the risk of myeloid neoplasms. He concludes that there  
is “little doubt” that benzene can cause neoplasms in the myeloid lineage.  
[58]  
[59]  
Accordingly, we find that – by analogy – the medical research supports a causal  
association between benzene exposure and mastocytosis.  
There are no other potential causes identified in the evidence  
We understand from the worker’s occupational medicine specialist’s opinion that  
there is no other identifiable cause more likely to have caused the worker’s  
systemic mastocytosis:  
[59.1]  
[59.2]  
In his December 14, 2018 report, he states, “. . . I also do not think that  
another identifiable exposure or factor is more likely to explain his  
mastocytosis, but of course often there is no identifiable causative factor in  
these cases.”  
He reiterates this opinion on September 27, 2019. He states that it is  
possible that the worker’s occupational exposures caused his systemic  
mastocytosis. He then reiterates that there is no other identifiable factor  
he would consider to be more likely to have caused the worker’s condition.  
Classification: Protected A  
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Decision No.: 2022-0288  
[59.3]  
His opinion remains unchanged in his December 10, 2019 response to the  
WCB medical consultant’s opinion. He states:  
“It remains my opinion, however, that it is possible that [the worker’s]  
occupational exposures (and specifically his exposure to benzene) have  
caused his systemic mastocytosis, but because of the paucity of specific  
evidence I cannot derive a dependable numerical risk estimate . . .  
As I have outlined previously, I do not think that there is any other clearly  
identifiable etiology of [the worker’s] systemic mastocytosis which I would  
consider more likely than his occupational exposure, but of course there  
often is no clearly identifiable cause in these cases.  
. . .  
Nonetheless, I would recommend that the possibility of occupational  
causation of [the worker’s] systemic mastocytosis, based on the general  
suitability of benzene to cause a range of hematopoietic malignancies, is  
considered in his claim adjudication.”  
[60]  
We acknowledge that the occupational medicine’s statements refer to the  
possibility of causation and that the “but for” test requires probability, not  
possibility. However, we understand these statements to refer to more than just  
mere possibility as the physician repeatedly notes that there is no other  
identifiable cause. We understand the physician’s use of the word “possible” to  
refer to the inability to address relative risk, not the worker’s specific situation.  
[61]  
This conclusion is supported to a minor extent by the worker’s hematologist, who  
notes that she can not totally exclude the worker’s occupational exposure as  
contributing to his development of systemic mastocytosis.  
[62]  
[63]  
We find it significant that there are no other potential causes identified in the  
evidence.  
We do not understand the WCB medical consultant’s January 16, 2019 opinion  
to describe other causes of the worker’s mastocytosis. In that opinion, the  
medical consultant explains that mastocytosis results from both chronic and  
episodic mast cell-mediator release and excessive mast cell accumulation in one  
or more tissues. He also provides a list of triggers that can precipitate mast-cell  
activation (including insect stings, drugs, temperature changes, mechanical  
irritation, and others such as alcohol, stress and infections). What the opinion  
does not do, however, is link these triggers (and responses) to the genetic and  
molecular abnormalities involved in mastocytosis.  
Conclusion  
[64]  
In summary, we find that the worker’s systemic mastocytosis has been caused  
by his occupational exposure to benzene. The weight of the evidence before us  
shows that, on a balance of probabilities, but for the worker’s occupational  
Classification: Protected A  
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Decision No.: 2022-0288  
exposures he would not have developed the disease. While there is no research  
related to the worker’s rare condition specifically, other research associates  
benzene exposures to other blood conditions and apply by analogy. Further, the  
medical opinions before us indicate that occupational exposures are the most  
likely cause of the worker’s mastocytosis and do not identify any other probable  
cause.  
Decision  
[65]  
[66]  
The worker has an acceptable Workers’ Compensation Board claim for systemic  
mastocytosis.  
The appeal is allowed. The April 1, 2020 decision of the Dispute Resolution and  
Decision Review Body is reversed.  
This decision is made with the full agreement of the hearing panel.  
Decision signed in Edmonton, Alberta on July 6, 2022.  
M. McAvoy  
Commissioner  
(on behalf of the panel)  
Hearing Panel:  
J. Keil  
M. McAvoy  
J. McKenna  
– Hearing Chair  
– Commissioner  
– Commissioner  
Typed by: imc/fw  
E_DEC08D (20210701)  
Classification: Protected A  
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Decision No.: 2022-0288  
Appendix A  
Legislation – Workers’ Compensation Act, RSA 2000, c W-15 (WCA)  
Section 1(1) of the WCA states, in part:  
[A1]  
“Interpretation  
. . .  
(a) ‘accident’ means an accident that arises out of and occurs in the  
course of employment in an industry to which this Act applies  
and includes:  
(i)  
a wilful intentional act, not being the act of the worker who  
suffers the accident,  
(ii) a chance event occasioned by a physical or natural cause,  
(iii) disablement, and  
(iv) a disabling or potentially disabling condition cause by an  
occupational disease;”  
[A2]  
Section 13.2(6)(b) of the WCA states, in part:  
“(6) In the hearing of an appeal under this section, the Appeals  
Commission  
. . .  
(b) is bound by the board of directors’ policy relating to the matter  
under appeal,”  
[A3]  
Section 24(1) of the WCA states:  
“Eligibility for compensation  
24(1)Subject to this Act, compensation under this Act is payable  
(a) to a worker who suffers personal injury by an accident, unless  
the injury is attributable primarily to the serious and wilful  
misconduct of the worker, and  
(b) to the dependants of a worker who dies as a result of an  
accident.”  
[A4]  
Section 24(6) of the WCA states:  
“(6) If a worker suffers disablement from or because of any occupational  
disease and at some time during the 12 months preceding the  
disablement was employed in an industry or process or performed  
activities deemed by the regulations to have caused that disease or  
Classification: Protected A  
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Decision No.: 2022-0288  
condition, the disease or condition is deemed to have been caused by  
that employment or activity, unless the contrary is shown.”  
Classification: Protected A  
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Decision No.: 2022-0288  
Appendix B  
Regulations  
Workers’ Compensation Regulation, AR 325/2002 (the Regulation)  
Section 20 of the Regulation states:  
[B1]  
“Occupational diseases  
20(1) For the purposes of this Act and this Regulation, ‘occupational  
disease’ means  
(a) a disease or condition listed in Column 1 of Schedule B that is  
caused by employment in the industry or process listed opposite  
it in Column 2 of Schedule B, and  
(b) any other disease or condition that the Board is satisfied in a  
particular case is caused by employment in an industry to which  
the Act applies.  
(2) For the purposes of subsection (1)(a), employment or process  
(a) listed in Column 2 of Schedule B and  
(b) in the manner and circumstances set out in Column 2 of  
Schedule B  
shall, unless the contrary is proven, be deemed to be the cause of  
specified disease or condition listed opposite it in Column 1 of Schedule  
B.”  
[B2]  
Schedule B of the Regulation states, in part:  
“COLUMN 1  
COLUMN 2  
DESCRIPTION OF DISEASE OR  
CONDITION  
INDUSTRY OR PROCESS  
1 Poisoning by  
. . .  
1 An Industry or Process  
. . .  
(g) Organic solvents (n-hexane,  
carbon tetra-chloride,  
trichloroethane, trichloroethylene,  
acetone, benzene, toluene, xylene  
and others);  
(g) where there is significant  
occupational exposure to  
organic solvents;”  
Classification: Protected A  
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Decision No.: 2022-0288  
Appendix C  
Workers’ Compensation Board Policies and Information Manual  
In effect as of the WCB case manager’s January 6, 2020 decision  
[C1]  
Policy 02-01 Part I, Arises out of and Occurs in the Course of Employment  
(Issue Date: April 3, 2018):  
“POLICY:  
To be considered compensable, an accident must meet two conditions: it  
must arise out of and occur in the course of employment. When WCB is  
notified of an accident, it initiates inquiries to obtain all relevant evidence,  
and adjudicates the eligibility of the claim based on the weight of that  
evidence.  
. . .  
INTERPRETATION  
1.0  
Accident  
‘Accident’ is used in the usual and ordinary sense, and means an  
unexpected mishap or event. For the purposes of workers’  
compensation, ‘accident’ also includes the circumstances defined in the  
four subclauses of [section] 1(1)(a) of the WCA.  
2.0  
Arises out of Employment  
An accident arises out of employment when it is caused by some  
employment hazard. An employment hazard is defined as an  
employment circumstance which presents a risk of injury or occupation  
(for example, machinery, chemicals, worksite ergonomics), or may be  
incidental (for example, weather conditions, insect bites, third-party  
vehicles).  
Personal Risks and Conditions  
Risks or conditions which are personal to the worker (such as the  
worker’s physical condition or personal relationships) are not hazards of  
employment unless employment factors contribute to the occurrence of  
injury (see Part II, Applications 1 and 4).  
3.0  
Occurs in the Course of Employment  
An accident occurs in the course of employment when it happens at a  
time and place consistent with the obligations and expectations of  
employment. Time and place are not strictly limited to the normal hours  
of work or the employer’s premises, however, there must be a  
relationship between employment expectations and the time and place  
the accident occurs (see Part II, Applications 2 and 3).  
Classification: Protected A  
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Decision No.: 2022-0288  
4.0  
Evidence  
Evidence includes accident reports, witness reports, medical information,  
and accepted medical opinion, as well as any other facts relevant to the  
accident.  
If the information received on the required reports is not sufficient to  
adjudicate the claim, WCB is responsible for gathering additional evident  
relevant to the claim.”  
[C2]  
Policy 02-01, Part II, Application 7, Causation (Issue Date: April 3, 2018):  
“APPLICATION 7: CAUSATION  
1.  
Why is causation important?  
Workers’ compensation compensates workers only for injuries and  
diseases that are work related (arise out of and occur in the course of  
employment). Therefore, it is a legislative requirement that the injury or  
disease be caused by work, so in every case, WCB must determine the  
cause of the injury or disease.  
In many cases, causation is clear and easily understood; for example, if a  
construction worker falls off a ladder at work and breaks his arm.  
In other cases, causation is more difficult to determine, particularly when  
there are multiple risk factors that may have caused or contributed to the  
injury or disease.  
2.  
What factors does WCB consider when determining  
causation?  
In determining causation, WCB considers a number of factors. These  
can be grouped into three categories:  
Medical diagnosis – what is the diagnosis? Is it a recognized medical  
diagnosis? Is the diagnosis clearly established in this particular case:  
Work factors – what are the conditions at the workplace? What are  
the worker’s duties? What are the physical demands? What type and  
extent of exposures are there?  
Personal Factors – does the worker’s medical condition predate the  
accident? Are there non work-related risk factors that may have  
caused the injury or disease?  
WCB reviews all these factors to determine if the worker’s injury or  
disease is work-related (meets the standard of causation).  
3.  
What is a standard of causation?  
A standard of causation is the legal standard or legal test that is applied  
to determine whether the injury or disease is caused by work (that is, to  
have arisen out of and occurred in the course of employment.  
Classification: Protected A  
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Decision No.: 2022-0288  
4.  
What standard of causation does WCB apply?  
The standard of causation used by WCB is the ‘but for’ test, except when  
specifically stated otherwise.  
5.  
What is the ‘but for’ test?  
The ‘but for’ test is a finding of fact – the work exposures were necessary  
for the accident and injury to occur. In other words, if not for the work  
exposures, the injury or disease would not have happened.  
In some cases there may be several causes that meet the ‘but for’ test  
that work in combination to cause an injury. Work does not have to be  
the oly factor, or even the primary one, for the injury to be compensable.  
It must, however, be a necessary factor; if the injury or disability would  
have happened anyway, regardless of the work factor, it is not  
compensable.  
The finding of fact is based on the evidence and accepted medical  
knowledge, not on a speculative connection.  
6.  
How does the balance of probabilities apply when  
determining causation?  
The balance of probabilities is the standard of proof used by WCB-  
Alberta.  
For example, when adjudicating a claim where the standard of causation  
is the ‘but for’ test, WCB weighs all the evidence and determines if it is  
more likely than not that, but for the worker’s employment, the injury  
would not have occurred (see also Policy 01-03, Benefit of Doubt).  
7.  
Under what circumstances does WCB use as a standard of  
causation other than the ‘but for’ test?  
WCB uses a modification of the ‘but for’ test or, in some cases, a different  
standard of causation for occupational diseases and injuries in the  
following circumstances:  
Presumptions  
Certain occupational disease are covered by presumptions contained in  
the WCA and WC Regulation (see [sections] 24(6), 24.1, and 24.2 of the  
WCA; [section] 20 and schedule B of the WC Regulation; and the  
Firefighters’ Primary Site Cancer Regulation). When the criteria set out in  
the WCA and the WC Regulation are met, it is presumed that the ‘but for’  
test has been met and the disease or condition was caused by the  
worker’s employment. A presumption may be rebutted if the evidence  
shows that, in a particular case, the disease was caused by a non-work  
exposure.  
If the disease or condition is listed in the presumptions but the criteria are  
not met in a particular case, the case is adjudicated on its own merits,  
Classification: Protected A  
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Decision No.: 2022-0288  
using the appropriate standard of causation as set out in the other  
sections of this policy.  
. . .  
Multiple Risk Factors and Actual Cause Cannot be Determined  
There are some diseases, primarily cancers, where it is impossible to  
determine the actual cause. An individual may have several risk factors,  
any one or any several of which may have caused the disease. There is  
an element of chance or randomness as to which of the risk factors  
caused the disease in a particular individual.  
The ‘but for’ test is a finding of fact. In this situation, it cannot be factually  
determined which of the risk factors caused the disease in the individual,  
so WCB must use a different causation test.  
For these diseases, WCB determines whether work factors materially  
contributed to the risk that the individual would develop the disease.  
Epidemiological studies identify the risk factors and provide an estimate  
of the probability that a particular risk factor, if present, would have  
caused the disease. WCB considers all the available epidemiological  
evidence regarding the relative risk (likelihood) that an occupational  
exposure was the cause of a particular disease in a particular individual.  
Where an occupational exposure has been established, a relative risk of  
2.0 or higher makes it more likely than not that the worker’s occupational  
exposure materially contributed to the worker’s risk of developing the  
disease.  
[C3]  
WCB Policy 03-01, Part I, Injuries (Issue Date: September 5, 2018):  
“POLICY:  
WCB will determine whether an injury has occurred as the result of a  
compensable accident, and will adjudicate appropriate compensation and  
services from the date of accident. WCB may also consider a second  
injury compensable if it is the direct result of the original compensable  
injury.  
When determining its responsibility, WCB will evaluate the relationship  
between the injury and the compensable accident. In second injury  
cases, WCB will evaluate the relationship between the original  
compensable injury and the second injury.  
This policy is effective February 1, 2012, except when noted otherwise in  
a specific policy section(s).  
INTERPRETATION  
1.0  
Injury  
Under [section] 24 of the Workers’ Compensation Act (WCA),  
compensation is payable to a worker who suffers personal injury by an  
Classification: Protected A  
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Decision No.: 2022-0288  
accident. Injuries may be either physical or psychological. They may be  
the immediate result of an accident or develop over time.  
. . .  
4.0  
Relationship Between the Injury and the Compensable  
Accident  
Many injuries (e.g., strains, sprains, burns, cuts, etc.) have an obvious  
relationship to the compensable accident; consequently, determining  
WCB’s level of responsibility is relatively simple. However, there are  
other injuries which, because of their progressive nature or less obvious  
relationship to employment, require consideration of relevant factors both  
in and outside employment which may have contributed to or caused the  
injury (see Part II, Application 1, Relationship to Compensable Accident).”  
[C4]  
Policy 03-01, Part II, Application 1, Relationship to Compensable Accident  
(Issue Date: July 4, 2018):  
“1.  
Why is the relationship of injury to compensable accident  
important?  
To be compensable, an injury must be the result of an accident as  
defined under Policy 02-01, Arises Out of and Occurs in the Course of  
Employment. Therefore, when adjudicating the eligibility of a claim, WCB  
looks at the nature of the injury and its relationship to the compensable  
accident.  
Often there is an obvious relationship between the nature of the injury  
and the compensable accident (e.g., a firefighter is burned when fighting  
a fire). However, the relationship is not always obvious. In these cases,  
there is a need for additional information, especially medical information,  
to establish the relationship to the compensable accident. For example,  
many occupational diseases have a long latency period. WCB’s inquiries  
must establish whether the work-related exposure was sufficient to cause  
the condition (see Application 3, Occupational Disease).  
2.  
How does WCB adjudicate injuries?  
In general, every claim is subject to a similar adjudicative process. The  
relationship between the injury and the compensable accident is  
examined to determine entitlement. Additional medical advice is sought  
on an as-needed basis. Complex claims may require additional  
investigation to determine work-relatedness.  
Special requirements for some types of injuries (e.g., cardiac,  
occupational disease) are given in Applications 2 to 8 . . .”  
Classification: Protected A  


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