Appellants, George Bint and Edwin Dalton, seek worker’s compensation benefits from respondent, Creative Forest Products (CFP), for damages they suffered as a result of exposure to red cedar dust while they were employed at CFP. CFP manufactures patio furniture from cedar.
George Bint began working at CFP on January 6, 1982. Bint testified that on or about the 7th or 8th of February, 1982, he began having a sore throat, and within four to five days had a severe cough and chest pains. He began coughing up phlegm and sawdust and had a runny nose. Several times he lost his voice. CFP owner, Brian Soptyk, told Bint he should see a doctor, and Bint testified that Soptyk set up an appointment with Doctor Venning for him on March 9. Doctor Venning saw Bint on March 9. He diagnosed Bint as suffering from an occupational illness caused by his exposure to the cedar dust at CFP. He advised Bint not to return to work. Bint did not return to work, and consequently, *118his last day at CFP was March 9, 1982. Bint was also examined by Doctor Torrington who characterized his occupational disease' as “non-acute,” in that it had an insidious onset rather than an acute onset.
The time sheets from CFP show that during the 68-day period from January 6, 1982, through March 9, 1982, Bint worked on 59 calendar days. Bint testified, however, that, he was on call 24 hours per day, and sometimes went in for short periods without punching in. Additionally, the time sheets reflect that Bint on several occasions worked from 10 to 19 hours per shift.
Bint filed a claim for worker’s compensation benefits. Respondents moved to dismiss pursuant to the 60-day exposure requirement of I.C. § 72-439. A hearing was held on this issue. The Commission found that Bint worked a total of 59 calendar days for the employer; that Bint did have an occupational disease; and that the occupational disease was non-acute. The Commission dismissed Bint’s claim pursuant to I.C. § 72-439, for failure to meet the 60-day exposure requirement.
Edwin Dalton began working at CFP on December 7, 1981. He continued working until January 12, 1982, when he suffered an injury to his finger. He was off work for approximately two months as a result of that injury. He returned to work on March 15, 1982, and worked through April 23, 1982. The time sheets from CFP indicate that Dalton worked a total of 48 shifts on 51 calendar days. On 11 occasions, Dalton reported for work but did not work due to machine breakdowns.
Prior to his employment at CFP, Dalton had chronic lung disease. As a result of his exposure to red cedar dust at CFP, Dalton developed an allergy which led to asthma. Due to his respiratory problems Dalton ceased work at CFP on April 23, 1982. He was advised by his doctor to stay away from red cedar dust.
Dalton filed a claim for worker’s compensation benefits. The Industrial Special Indemnity Fund was made a party to his action because Dalton alleged he was totally and permanently disabled as a result of the combined effect of his allergy to red cedar dust and his pre-existing impairment. Respondents move to dismiss pursuant to the 60-day exposure requirement of I.C. § 72-439. The Commission found that Dalton worked a total of 48 shifts at CFP; that he did have an occupational disease; that the disease was non-acute; and that as a result of his pre-existing lung disease and the occupational disease he has a permanent-partial impairment equal to 10% of the whole person. The Commission dismissed Dalton’s claim for failure to meet the 60-day requirement of I.C. § 72-439. Dalton’s and Bint’s claims were consolidated for purposes of this appeal:
Appellants present three issues on appeal: (1) Did the Industrial Commission err in its finding that claimants’ occupational diseases were non-acute for purposes of applying I.C. § 72-439? (2) Did the Industrial Commission err in concluding that claimants had not met the 60-day exposure requirement? (3) Does the 60-day exposure requirement for non-acute diseases violate the fourteenth amendment to the United States Constitution, and article 1, sections 2 and 13 of the Idaho Constitution? We will address each issue in turn.
Appellants first contend that the Commission erred in its finding that their diseases were non-acute. I.C. § 72-439 provides that “[a]n employer shall not be liable for any compensation for a non-acute occupational disease unless the employee was exposed to the hazard of such disease for a period of sixty (60) days for the same employer.” The Idaho worker’s compensation statutes do not provide a definition of the terms “acute” or “non-acute.” The applicable dictionary definition of the term “acute” is “having a sudden onset, sharp rise, and short course.” Webster’s New Collegiate Dictionary 13 (1981 ed.). Similarly, the medical world defines an “acute” disease in terms of a short and sharp course: “Of short and sharp course, not chronic; said of a disease.” Stedman’s Medical Dictionary 20 (4th Lawyers ed. 1976).
*119The medical testimony in both cases indicates that appellants suffered from non-acute occupational diseases. Doctor Torrington was the medical expert who testified in both cases. He stated that, based on the medical literature, the majority of patients who develop red cedar induced asthma do so after a period of time, usually over a period of several months. For that reason, he testified that the disease was chronic rather than insidious. As to both appellants, he testified that because their symptoms developed gradually, over a period of several weeks or months, he would characterize their disease processes as non-acute.
Based ? on the above testimony, the Commission found, in both cases, that the diseases were non-acute for purposes of applying I.C. § 72-439. The Commission’s findings are supported by the evidence in both cases. Where contested findings of the Commission are supported by substantial, competent evidence, those findings will not be disturbed on appeal. I.C. § 72-732(1); In re Chavez, 104 Idaho 279, 658 P.2d 950 (1983); Bush v. Bonners Ferry School Dist. No. 101, 102 Idaho 620, 636 P.2d 175 (1981). Therefore, we hold that the Commission did not err in determining that, under I.C. § 72-439, appellants’ diseases were non-acute.
Appellants next contend that the Commission erred in concluding that they had not met the 60-day exposure requirement. Like the word “non-acute,” the word “day” is not defined in the worker’s compensation statutes. Appellants ask this Court to hold that “days of exposure” may refer to different time frames depending on the facts presented. Appellant Bint asserts that in his case we should define days of exposure as “equivalent work days.” It is his position that a day of exposure refers to an 8-hour work day and that on those days where he worked in excess of eight hours, he should be credited with more than a single day of exposure. Appellant Dalton, on the other hand, urges that in his case a day of exposure should be interpreted as a calendar day. Dalton worked 48 shifts on 51 days and seeks credit for 51 rather than 48 days of exposure. We decline to adopt such an inconsistent position.
We note that the Industrial Commission did apply a different legal standard to determine the number of days of exposure in the two hearings, albeit, not in the way the appellants wished. In Bint’s case, the Commission determined that a day of exposure meant a calendar day of work, regardless of whether an employee worked more or less than eight hours. In Dalton’s case, the Commission ruled that the number of days of exposure was to be determined by the number of shifts worked.
We believe that the legislature intended a day of exposure to refer to a calendar day of work. If the 60-day requirement were to be measured by an 8-hour work shift, problems would arise in determining how to count exposure on the days where an employee worked more than or less than eight hours. For example, where an employee worked less than eight hours on a given calendar day, would he be credited with one-half day of exposure, or a fractional portion of the day calculated by the ratio of his hours worked over the total hours? We do not believe that the legislature intended to create such a factual morass. The calendar day rule eliminates the procedural technicalities called for by the appellants’ position. It also gives workers the benefit of the doubt in those cases where they have worked less than an eight-hour shift on a given day or where their shift started on one day and ended on another. Consequently, we hold that a day of exposure, under I.C. § 72-439, means a calendar day of work.
Additionally, appellants contend that a day of exposure should be interpreted broadly enough to include days on which appellants reported to work but did not actually work, and even days on which appellants did not report to work at all. (The last contention is based on the fact that appellants carried some cedar dust in their lungs throughout the entire period they were employed at CFP. Thus, appellants contend they continued to be exposed *120on those days when they did not work.) We decline to adopt such a broad interpretation of the exposure requirement.
In our view, a worker is exposed to the hazards of an occupational disease only on those days he works within the hazardous environment. Thus, we hold that the 60-day exposure requirement under I.C. § 72-439 means that an employee must have worked on 60 calendar days for the same employer before the employer is liable for worker’s compensation. This view is consistent with our earlier decisions. Jones v. Morrison-Knudsen Co., Inc., 98 Idaho 458, 567 P.2d 3 (1977); See McLean v. Hecla Mining Co., 62 Idaho 75, 108 P.2d 299 (1941).
In McLean, supra, we held that although more than 60 days had elapsed between the date of hire and the date of discharge, the individual had worked only 45 days and, thus, was not entitled to compensation. Similarly, in Jones v. Morrison-Knudsen, supra, we held that I.C. § 72-439 requires 60 days of exposure to the hazardous environment and directed the Commission to count the number of exposures.
Appellants’ final contention is that I.C. § 72-439 is unconstitutional on both equal protection and due process grounds. Appellants first assert that the statute violates the equal protection clauses of the United States and Idaho Constitutions in that it establishes an unreasonable classification between workers with acute and workers with non-acute occupational diseases. Since I.C. § 72-439 creates no suspect, “near” suspect, or invidiously discriminatory classification and since it does not involve a fundamental or “quasi” fundamental right, the proper standard for equal protection review is the “rational basis test.” Heese v. A & T Trucking, 102 Idaho 598, 600, 635 P.2d 962, 964 (1981). See also LePelley v. Grefenson, 101 Idaho 422, 614 P.2d 962 (1980); Jones v. State Board of Medicine, 97 Idaho 859, 555 P.2d 399 (1976), cert. denied, 431 U.S. 914, 97 S.Ct. 2173, 53 L.Ed.2d 223 (1977). Under the “rational basis test,” a classification will withstand an equal protection challenge if there is any conceivable state of facts which will support it. State v. Bowman, 104 Idaho 39, 41, 655 P.2d 933, 935 (1982); School Dist. No. 25, Bannock County v. State Tax Commission, 101 Idaho 283, 288, 612 P.2d 126, 131 (1980).
Appellants assert that the distinction between acute and non-acute diseases is arbitrary and without a reasonable relationship to the purpose of the worker’s compensation laws. The purpose of worker’s compensation is to provide compensation for “injuries received and occupational diseases contracted in industrial and public work____” I.C. § 72-201 (emphasis added). Worker’s compensation does not purport to be a social insurance program covering all a worker’s health problems. The legislature has a legitimate interest in seeing that coverage for occupational diseases be kept within reasonable limits and in controlling the financial impact on Idaho industry and consumers. The legislature might have determined that these interests made it reasonable to establish a condition precedent of 60 days exposure before imposing liability for non-acute occupational diseases. The legislature might also have determined that it would be unfair to impose liability on employers for time-related diseases without imposing a corresponding time requirement on the employment relationship.
As we stated above, one of the principal distinctions between an acute and non-acute illness is the length of onset time. An acute illness is characterized by a sudden onset, while a non-acute illness develops more gradually, generally over a period of weeks or months. Given the time-related nature of non-acute illnesses, it seems reasonable for the legislature to impose a time requirement before the right to worker’s compensation benefits accrues.
Historically, occupational disease coverage has lagged behind accidental injury • coverage. There were various reasons for the lag. One reason was the view that while accidental injuries were known to the common law, the concept of occupational disease was unknown. To the extent that *121worker’s compensation was seen as substituting non-fault liability for injuries potentially subject to fault liability, there was thought to be no place for occupational diseases. Another reason was hesitation over whether a problem as generalized and extensive as occupational disease could be effectively dealt with under workers’ compensation. The final, and perhaps the most compelling, reason was the fear that the heavy incidence of occupational disease would place an unbearable burden on the compensation system. IB A. Larson, Workmen’s Compensation Law § 41.20 (1982).
Idaho adopted its first occupational disease statute in 1939, the Occupational Disease Compensation Law. 1939 Idaho Sess. Laws, ch. 161, at 286. This Court has previously recognized that the statute was a departure from the original Compensation Act, which did not provide compensation for occupational diseases, and has shown deference to the limitations promulgated by the legislature for administering the Act. In Habera v. Polaris Mining Co., 62 Idaho 54, 108 P.2d 297 (1940), we stated:
“This statute is a departure from the original compensation law and is intended to include certain occupational diseases in the list of compensable accidents not theretofore covered. In attempting to do so, the legislature evidently anticipated difficulty in the application and administration of such an act unless very definite bounds were fixed within which it might operate. It accordingly prescribed certain limitations and prohibitions ____” Id. at 56, 108 P.2d at 298.
The Act extended coverage to a specific list of occupational diseases. It also provided various limitations on coverage including the 60-day exposure requirement. The 60-day rule has remained a part of Idaho law ever since. It was re-enacted in its present form in 1971. 1971 Idaho Sess.Laws, ch. 124, § 3, at 424. While we recognize that the 60-day exposure requirement may, in some cases, mandate harsh results, it is not our function to adjudge the wisdom of I.C. § 72-439. We are concerned only with its constitutionality: whether it is unreasonable, arbitrary, capricious or discriminatory. It will not be held to be so where it reflects a reasonably conceivable, legitimate public purpose. State v. Bowman, 104 Idaho at 42, 655 P.2d at 936; State v. Cantrell, 94 Idaho 653, 655, 496 P.2d 276, 278 (1972). As we stated above, it seems reasonable for the legislature to impose a time requirement before providing compensation for diseases which take a considerable period of time to develop. Thus, we hold that I.C. § 72-439 does not violate the equal protection clause of either the United States or Idaho Constitutions.
Appellants further assert that the statute violates the due process clauses of the two constitutions by establishing an irrebutable presumption that causation is lacking whenever a claimant with a non-acute occupational disease has worked less than 60-days. The applicable standard of analysis under a due process challenge is the same as under an equal protection challenge: whether the challenged law bears a rational relationship to a legitimate legislative purpose. Heese v. A & T Trucking, 102 Idaho 598, 635 P.2d 962; Jones v. State Board of Medicine, 97 Idaho 859, 555 P.2d 399. For the reasons stated above, we hold that I.C. § 72-439 survives a due process challenge as well.
The decisions of the Industrial Commission are affirmed.
No attorney fees on appeal.
Costs to respondent.
SHEPARD and BAKES, JJ., concur.