97-272

 No. 97-272

 IN THE SUPREME COURT OF THE STATE OF MONTANA

 

1997

WILLIAM POLK, 

 Petitioner and Appellant, 

 v.

PLANET INSURANCE CO.,

Insurer and Respondent,

 KOCH AGRICULTURE, INC.,

 Employer.

APPEAL FROM: Workers' Compensation Court, State of Montana

 Honorable Mike McCarter, Judge Presiding.

COUNSEL OF RECORD:

 For Appellant:

 Lawrence A. Anderson, Howard F. Strause, Attorneys at Law,

 Great Falls, Montana

 For Respondent:

 Sara R. Sexe; Marra, Wenz, Johnson & Hopkins, 

 Great Falls, Montana

 Submitted on Briefs: November 13, 1997

 Decided: December 30, 1997 

Filed:

 __________________________________________

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 Clerk

Justice W. William Lepahart delivered the Opinion of the Court.

 Appellant William Polk (Polk) appeals from the February 26, 1997, Judgment and

Order of the Montana Workers' Compensation Court, affirming the findings of fact,

conclusions of law, and final order of the hearings examiner of the Department of 

Labor.

 Polk raises the following issues on appeal:

1. Did the Workers' Compensation Court err in holding that Polk had failed to prove

causation?

2. Did the Workers' Compensation Court err in holding that the unlawful medical panel

procedure was not reversible error?

3. Did the Workers' Compensation Court err in reviewing the decision of the hearings

examiner under the clearly erroneous standard of review?

Because we find issues one and three dispositive, we will not address issue two.

 Factual and Procedural Background 

 Koch Agriculture, Inc. (Koch) owns a Great Falls factory which processes seeds,

such as flax, rape, linseed, and mustard, into oil and meal sold for cattle feed. 

Appellant

William Polk (Polk) worked in the factory owned by Koch and its predecessors from

1985 to 1993. Polk performed physical labor at the factory, including carrying and

stacking meal sacks, shoveling seed, sacking and unsacking meal, blowing dust residue

off of the walls, and cleaning the machinery. Polk also scraped moldy grain from the

inside of elevator and machine pits. 

 Koch's factory is housed in one building, which is 150 feet long and 70 feet 

wide. 

The building has one two-foot ventilation fan on the ceiling. Because the process of

transporting, cleaning, and milling the seeds generates dust, additional fans were

occasionally brought in to blow the airborne dust away from workers. Though Polk's 

job

subjected him to dust, fumes, and airborne mold, Koch did not provide him with a dust

mask until 1992. After 1992, Polk was given a paper mask, which often became clogged

with dust and sweat after a few hours. 

 In April 1991, Polk began experiencing health problems. He suffered from 

chills,

fever, and persistent diarrhea. In February 1992, Polk was hospitalized for fever 

and

chills. He testified that thereafter he "never felt good." He tired easily, had 

trouble

breathing, and lost nearly 40 pounds. In November 1993, Polk was again hospitalized

for ten days for fever, chills, and a cough. Shortly after, Polk's doctor ordered 

him to

leave work.

 Polk continues to suffer severe shortages of breath and lightheadedness. He has

lost nearly half of his lung function, and his low blood oxygen level frequently 

requires

him to use supplemental oxygen. For about 30 years, Polk smoked one and a half packs

of cigarettes a day. He attempted to quit smoking in December 1993, but still smokes

occassionally. 

 In January 1994, Polk filed a claim for occupational disease benefits against 

Koch

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and its insurer, Respondent Planet Insurance Company (Planet). Pursuant to õõ 39-72-

601 through -613, MCA, the Department of Labor and Industry appointed a panel of

three doctors to evaluate Polk's claim. Polk was examined by Drs. David Anderson and

J. Michael Sadaj. Dr. Anderson concluded that Polk suffered from an occupational

disease, while Dr. Sadaj concluded he did not. A third physician, Dr. Thomas 

Thigpen,

reviewed the records and reports of Drs. Anderson and Sadaj. Dr. Thigpen did not 

meet

with the other two doctors, but issued a report to the Department of Labor on behalf 

of

the panel concluding that Polk's condition was not the result of an occupational 

disease. 

Polk appealed this determination to the hearings unit of the Department of Labor and

Industry. 

 The eight medical experts whose testimony was presented at the hearing had 

either

examined Polk or reviewed his medical records. Each came to a different conclusion 

as

to the cause of Polk's pulmonary condition. Dr. Anderson, a panel doctor, concluded

that Polk's condition was caused primarily by asthmatic bronchitis, hypersensititivy

pneumonitis, and some emphysema. Hypersensitivity pneumonitis, or "farmer's lung,"

can be caused by exposing the lungs to grain, molds, and other airborne irritants. 

Emphysema is typically caused by smoking. Dr. Anderson stated that the asthmatic

component of Polk's condition was "likely related to his exposure to toxic organic 

dusts." 

Drs. Sadaj and Thigpen, the other panel doctors, concluded that Polk suffers from

"chronic obstructive pulmonary disease and chronic respiratory insufficiency as a 

result

of long term heavy smoking." 

 Polk's treating physician, Dr. Holly Strong, concluded that Polk suffers from

hypersensitivity pneumonitis, occupational asthma, and slight emphysema. She also

diagnosed Polk with bronchiectasis, which can be caused by fungus associated with

organic dust and by hypersensitivity pneumonitis. Dr. Jeffrey Kessler, a 

radiologist,

performed a high-resolution CT scan on Polk's lungs and determined that Polk suffers

from hypersensitivity pneumonitis, severe bronchiectasis, and minimal emphysema. 

 Dr. Stephen Demeter, an expert retained by Planet, testified that he found no

evidence that Polk suffers from hypersensitivity pneumonitis, or of any occupational

disease. He concluded that Polk has emphysema caused by smoking and some

bronchiectasis, possibly caused by a past episode of pneumonia. Planet also offered 

the

expert deposition testimony of Dr. Robert Merchant, who concluded that Polk suffers

from emphysema and some bronchiectasis. Polk's expert, Dr. Dana Headapohl,

concluded that Polk suffers from hypersensitivity pneumonitis caused by his exposure 

to

mold and organic dust while working at Koch.

 After a hearing, the hearings examiner found that Polk is not suffering from an

occupational disease. In March 1996, Polk appealed to the Workers' Compensation

Court, arguing that the procedure used by the three-member medical panel was unlawful

and that the hearings examiner had failed to apply the appropriate standard of 

causation. 

The Workers' Compensation Court held that the medical panel had acted improperly by

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failing to meet to discuss Polk's case, but that this was not reversible error. It 

further

found that the hearings examiner's finding that Polk does not suffer from an 

occupational

disease is not clearly erroneous and is supported by substantial evidence. Polk 

appeals

from this decision. 

 Standard of Review

 We review the Workers' Compensation Court's findings of fact to determine

whether the findings are supported by substantial credible evidence. This Court 

reviews

conclusions of law to determine whether the lower court's interpretation of the law 

is

correct. Kloepfer v. Lumbermen's Mut. Cas. Co. (1996), 276 Mont. 495, 916 P.2d

1310.

 Discussion

Did the Workers' Compensation Court err in holding that Polk had failed to prove

causation and in reviewing the decision of the Department of Labor under the clearly

erroneous standard?

 A. Appropriate Standard of Causation

 The Occupational Disease Act of Montana (the Act) is codified at Title 39, Ch. 

72,

MCA. To qualify for benefits under the Act, the claimant must prove that his or her

employment is a proximate cause of the claimant's condition. Under õ 39-72-408, MCA:

 Occupational diseases shall be deemed to arise out of the employment only

 if:

 (1) there is a direct causal connection between the conditions under

 which the work is performed and the occupational disease;

 (2) the disease can be seen to have followed as a natural incident of

 the work as a result of the exposure occasioned by the nature of the

 employment;

 (3) the disease can be fairly traced to the employment as the

 proximate cause;

 (4) the disease does not come from a hazard to which workmen

 would have been equally exposed outside of the employment;

 (5) the disease is incidental to the character of the business and not

 independent of the relation of employer and employee.

Polk recognizes that to prevail, he must prove that his lung condition was 

proximately

caused by his exposure to dust and other irritants at Koch. However, he asserts 

that the

hearings examiner and the four doctors who concluded that he did not suffer from an

occupational disease applied the wrong standard of causation. 

 Under Montana law, a worker may receive pro rata compensation "[i]f an

occupational disease is aggravated by any other disease or infirmity not itself 

compensable

or if disability or death from any other cause not itself compensable is aggravated,

prolonged, accelerated, or in any way contributed to by an occupational disease." 

Section

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39-72-706(1), MCA (emphasis added). " 'Occupational disease' means harm, damage,

or death . . . arising out of or contracted in the course and scope of employment and

caused by events occurring on more than a single day or work shift." Section 39-72-

102(10), MCA (emphasis added). Polk argues that in light of these statutes and our 

case

law construing them, he must only show that a work-related exposure aggravated or

contributed to his illness. He asserts that the testimony of several of the 

doctors, and in

turn the conclusion of the hearings examiner, was based on the misconception that to

satisfy causation, Polk had to prove that the occupational exposures were the major 

factor

causing his health problems.

 Indeed, this Court has held that "an employer accepts his employee with all of 

his

injuries and diseases" and, thus, that the test for compensability is whether the 

job-related

incident significantly aggravated the preexisting condition. Ridenour v. Equity 

Supply

Co. (1983), 204 Mont. 473, 665 P.2d 783; see also Eastman v. Atlantic Richfield Co.

(1989), 237 Mont. 332, 777 P.2d 862. For example, in Ridenour, 665 P.2d at 784, the

claimant was a long-term smoker who worked in a dusty grain-processing plant. After

an incident of grain inhalation, the claimant developed a cardiopulmonary disease. 

Ridenour, 665 P.2d at 784. This Court held that "diseases are subject to 

aggravation and

acceleration" and that the grain inhalation had aggravated the claimant's 

preexisting lung

disease. Ridenour, 665 P.2d at 788. Thus, we found that he was entitled to pro rata

compensation. Ridenour, 665 P.2d at 788.

 Planet argues that the aggravation statute does not relieve the claimant of the

burden of proving proximate cause, but that Polk is still required to prove a direct 

causal

connection between the work-related factors and his resulting condition. We agree 

with

Planet that the aggravation statute, õ 39-72-706, MCA, does not circumvent the

proximate cause requirement of õ 39-72-408, MCA. However, Planet contends that to

prove proximate cause, Polk must show that occupational exposures were a substantial

contributing factor to his health problem. 

 In light of the proximate cause statute and the aggravation statute, we agree 

with

the Workers' Compensation Court that "occupational aggravations of preexisting nonoccupational diseases are compensable, as are occupational diseases which are 

aggravated

by non-occupational factors." As we held in Ridenour, the test for compensability 

under

the Act is whether occupational factors significantly aggravated a preexisting 

condition,

not whether occupational factors played the major or most significant role in 

causing the

claimant's resulting disease.

 Other jurisdictions, such as New Mexico, have come to the same conclusion when

considering the effect of numerous factors, occupational and non-occupational, on

pulmonary diseases:

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 These cases have dealt specifically with the analytical and testimonial

 difficulties inherent in determining compensability of diseases caused by the

 combined effect of smoking and work-related exposures to dust, asbestos,

 radiation, and various toxic fumes. . . . The majority rule in states with a

 statutory scheme similar to New Mexico's allows compensation without a

 showing that work-related exposures were the predominant cause of the

 disease or death.

Buchanan v. Kerr-McGee Corp. (N.M. App. 1995), 908 P.2d 242, 249. That court

noted that "[t]he work-related cause may, in fact, be a minor factor so long as the

worker establishes that, as a matter of medical probability, it was a cause of the

disability." Buchanan, 908 P.2d at 249.

 Therefore, we hold that Polk need not prove that occupational exposures were the

major or substantial factor causing his chronic pulmonary condition. Rather, Polk 

must

prove that he is suffering from a disease that is proximately caused by his 

employment

or that exposure to dust and other irritants while in the course of his employment 

at Koch

contributed to or aggravated a preexisting condition. Having stated the appropriate 

test

for causation, we proceed to apply it to this case.

 B. Workers' Compensation Court's Standard of Review

 The Workers' Compensation Court agreed that õ 39-72-408, MCA (proximate

cause) "must be read together with õ 39-27-706, MCA, which provides for apportionment

between occupational and non-occupational causes." Nonetheless, the Workers'

Compensation Court went on to hold that the findings of the Department of Labor's

hearings examiner were not clearly erroneous. 

 Under õ 39-72-612, MCA, the judge of the Workers' Compensation Court may

overrule the decision of the Department of Labor when it is:

 (a) in violation of constitutional or statutory provisions;

 (b) in excess of the statutory authority of the agency;

 (c) made upon unlawful procedure;

 (d) affected by other error of law;

 (e) clearly erroneous in view of the reliable, probative, and substantial

 evidence on the whole record; or

 (f) arbitrary or capricious or characterized by abuse of discretion or clearly

 unwarranted exercise of discretion.

The Workers' Compensation Court erred in reviewing only for clearly erroneous 

findings

of fact. Whether the hearings examiner applied the appropriate test for proximate

causation is a question of law. Thus, pursuant to õ 39-72-612, MCA, the Workers'

Compensation Court should have reviewed the Department of Labor's decision not only

for clearly erroneous findings of fact, but also to determine whether the decision 

was

affected by an error of law.C. Application of Appropriate Standard of Causation

in this Case

 As noted by the hearings examiner, "[e]xamination and analysis of [Polk]'s

condition as well as the cause of that condition by numerous doctors resulted in one 

group

of doctors concluding [Polk] suffers from an occupational disease and another group 

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of

doctors concluding [Polk] does not suffer from an occupational disease." Based on 

the

presumption of correctness given to the medical panel's adverse decision and on the

hearings examiner's determination that the doctors who found no occupational disease

were more qualified and presented better-reasoned conclusions, the examiner concluded

that Polk did not suffer from an occupational disease. Polk argues that had the 

hearings

examiner reviewed the evidence under the appropriate standard, to determine whether 

an

occupational exposure contributed to or aggravated Polk's condition, rather than 

simply

adopted these doctors' conclusion that Polk does not suffer from an occupational 

disease,

the balance of evidence would have been tipped in his favor.

 As stated above, each doctor came to different conclusions as to the cause of

Polk's pulmonary disease. As noted by Dr. Merchant, placing a name on the myriad of

symptoms Polk suffers is difficult: "[O]ne of the reasons that we term it 'COPD'

[chronic obstructive pulmonary disease] rather than . . . going past that and 

actually

saying, 'You have chronic bronchitis versus emphysema,' is that very often you have a

mixture of the various conditions, because some of the things that cause one of them 

can

also cause the others." 

 Four of the eight doctors involved in this case, Drs. Sadaj, Thigpen, Demeter, 

and

Merchant, concluded that Polk did not suffer from hypersensitivity pneumonitis, or 

any

other occupational disease. Based on their testimony, the hearings examiner 

concluded

that Polk was not entitled to compensation. However, the testimony of three of 

these

four doctors could support a finding that the conditions to which Polk was exposed at

Koch aggravated or contributed to his pulmonary condition.

 Dr. Merchant concluded that Polk suffers from emphysema and some

bronchiectasis. However, Dr. Merchant also testified that occupational exposures 

"would

be very likely to play a significant role in exacerbating [Polk's] emphysema." Dr.

Thigpen, the doctor who reported to the Department of Labor on behalf of the medical

panel, concluded that hypersensitivity pneumonitis was not the most likely cause of 

Polk's

pulmonary condition, but did not exclude it as a possibility. Further, Dr. Thigpen 

stated

that "if one does have any type of underlying lung disease (and that includes 

emphysema

and chronic bronchitis) exposure to various types of dust and other irritants will 

aggravate

claimant's condition." [Emphasis added]. Dr. Sadaj, another panel doctor, concluded

that Polk suffers from chronic obstructive pulmonary disease and chronic respiratory

insufficiency as a result of long-term heavy smoking. However, in support of this

conclusion, Dr. Sadaj testified: "The only way that I could say the occupation was a

major part in his problem was if he has hypersensitivity pneumonitis." 

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 As stated above, Polk need not prove that the occupational exposures, as 

compared

to smoking or other contributing factors, were the "major" or primary factor causing 

his

present condition. Rather, as long as occupational exposures substantially 

aggravated

Polk's pulmonary condition, he is entitled to pro rata compensation for his 

injuries. 

However, in concluding that he did not suffer from an occupational disease, Drs.

Merchant, Sadaj, and Thigpen were operating under the mistaken assumption that, to

qualify him for occupational disease benefits, Polk's exposure to dust and other 

irritants

at Koch had to be the major factor causing his pulmonary condition. When the 

testimony

of Drs. Merchant, Sadaj, and Thigpen is reviewed under the correct standard of 

causation

and added to the testimony of the four doctors who concluded that Polk indeed suffers

from an occupational disease, it could support a finding that occupational factors

contributed to or aggravated Polk's pulmonary disease. 

 By adopting the doctors' threshhold requirement that Polk's occupational 

exposures

be the major or primary factor causing his medical condition rather than reviewing 

their

testimony to determine whether it supports a finding that an occupational exposure

contributed to or aggravated Polk's condition, the hearings examiner applied the 

wrong

standard of causation. We hold that the Workers' Compensation Court erred in not

overruling the Department of Labor's decision based on this error of law. 

 Based on the foregoing, we reverse the decision of the Worker's Compensation

Court and remand to that court for further proceedings consistent with this opinion.

 /S/ W. WILLIAM LEAPHART

We concur:

/S/ J. A. TURNAGE

/S/ TERRY N. TRIEWEILER

/S/ JAMES C. NELSON

/S/ JIM REGNIER 

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