In case No. 18704, plaintiff Louis L. Chavez seeks reversal of a decision of the Industrial Commission that denied him permanent partial impairment benefits from the Second Injury Fund. His employer, Kaiser Steel Corp., in case No. 18703 joins Chavez in seeking a reversal of the denial of those benefits and, in addition, seeks reimbursement from the Second Injury Fund for a portion of the benefits it paid Chavez.
In 1977, while employed as a miner by Kaiser Steel Corp., Chavez injured his right knee when the empty mining car he was riding struck another empty car. He continued working the day of the injury and did not report the event until seven months later when his knee began to stiffen. He saw the company doctor who sent him to a specialist. The specialist performed a men-iscectomy in August 1978, and Chavez went back to work. After undergoing a second operation to alleviate the pain which continued in his knee, he did not return to the job.- He later underwent a third surgery but still suffers from degenerative arthritis of his knee. In 1946, Chavez had suffered a multiple rib fracture while working in the mines. The healing of the fracture resulted in a reduced functional capacity of his right lung.
The administrative law judge for the Commission appointed a special medical panel to determine the medical issues. The panel was of the opinion that a degenerative arthritic disease preexisted the 1977 accident and was the major cause of Chavez’s knee problems. Using a “Combined Values Chart,” the panel found Chavez was thirty-three percent impaired before the accident due to his arthritis and pulmonary condition. The contribution of the 1977 accident was found to be five percent of the lower extremity or two percent of the whole man.
The administrative law judge found that the two percent impairment was “minimal or ‘token’ ” and concluded that the 1977 incident did not result in a permanent partial incapacity greater than that previously existing. Consequently, he ruled that the Second Injury Fund had no liability. Since Kaiser had paid for Chavez’s temporary total disability and had made advance payments for his permanent partial disability, the administrative law judge also ruled that Chavez had been overcompensated and was not entitled to further benefits. (Because of the arthritis, Chavez receives social security disability; and, because of the pulmonary condition, he receives black lung benefits.) The Commission affirmed the administrative law judge.
I.
Chavez argues that the Commission erred in refusing to raise the panel’s determination of the percentage of his pulmonary impairment which existed prior to his 1977 industrial injury. He claims the error is apparent since the chairman of the medical panel admitted on cross-examination that American Medical Association (AMA) guides suggested a possible greater impairment than that found by the panel.
While disability claims are liberally construed in favor of awarding benefits, Prows v. Industrial Commission, Utah, 610 P.2d 1362 (1980), we do not overturn the Commission’s findings on appeal unless they are arbitrary or capricious, wholly without cause, contrary to the one inevitable conclusion from the evidence, or without any substantial evidence to support them. Kincheloe v. Coca-cola Bottling Co. of Ogden, Utah, 656 P.2d 440 (1982); Kaiser Steel Corp. v. Monfredi, Utah, 631 P.2d 888 (1981).
The chairman of the panel explained that the difference between the panel’s de*1170termination of Chavez’s impairment and the AMA’s guides were due to the age of the guides and to the recognition that they are based on more disabling, progressive congestive diseases (such as emphysema) than Chavez’s non-progressive restricted lung capacity. On redirect examination, the chairman stood firmly by the medical panel’s findings. Further, Chavez offered no evidence to contradict the chairman’s testimony. Based on this record, we cannot say that the Commission’s findings on Chavez’s preexisting pulmonary impairment were arbitrary or capricious. They were neither wholly without cause nor contrary to the one inevitable conclusion from the evidence. Rather, substantial evidence supports them. We therefore find no error on this point.
II.
Both Chavez and Kaiser maintain that the Commission erred in failing to find the Second Injury Fund liable. Workmen’s compensation must be paid by the Fund under U.C.A., 1953, § 35-1-69(1) when an employee with a previous permanent incapacity sustains an industrial injury “that results in permanent incapacity which is substantially greater than he would have incurred had he not had the pre-existing incapacity.” (Emphasis added.)
In denying Chavez compensation from the Second Injury Fund for his permanent partial impairment predating the 1977 accident, the administrative law judge and the Industrial Commission focused on whether the 1977 injury substantially increased his total impairment. Indeed, the basis of the Industrial Commission’s affirming the administrative law judge’s denial of compensation was that “the 2% disability assigned by the Medical Panel to the industrial accident does not represent a ‘substantially greater’ impairment than that which preexisted the industrial accident.” A dissenting commissioner wrote that he was “of the opinion that the 2% disability assessed to the industrial accident represents a definite and measurable increase in the disability of the Applicant and that the Second Injury Fund benefits should be awarded for the preexisting portion.” In their arguments on appeal, counsel for all parties have concentrated on whether the two percent increase in disability caused by the 1977 accident was “substantially greater” than the preexisting impairment.
The decisions of the administrative law judge and the Industrial Commission and the arguments of counsel misperceive the meaning of section 35-1-69. Second Injury Fund liability is imposed, not when the second injury itself causes a “substantially greater” incapacity, but when the worker’s total incapacity following the second injury is “substantially greater” than it would have been but for the preexisting incapacity. Thus, our attention should be directed to the contribution made by the preexisting incapacity. If the preexisting incapacity made the total resulting incapacity substantially greater, then the Second Injury Fund is liable. However, if the preexisting incapacity was minimal, it could not fairly be termed to have “substantially increased” the total incapacity that the worker now suffers.
This construction is entirely consistent with decisions of this Court involving the Second Injury Fund. In Intermountain Health Care v. Ortega, Utah, 562 P.2d 617 (1977), Mrs. Ortega sustained a twenty percent permanent partial disability when she strained her back lifting laundry bags in the plaintiff’s hospital. A panel also found that she had an additional ten percent impairment attributable to a preexisting psychological condition relating to pain in her back. In holding that the Second Injury Fund was liable for the ten percent, this Court said:
The requirement that the pre-existing condition combines with the later injury to cause a “substantially greater” permanent incapacity does not mean that the former must be greater than the latter. It simply means that it be some definite and measurable portion of the causation of the disability. It surely cannot be doubted that 30% is substantially greater than 20%, nor that 10% disability is itself *1171substantial in that it is definite and measurable. Consequently, inasmuch as it appears that the pre-existing condition increased the resulting disability by one third [sic], it follows that under the requirements of the statute, the medical expenses as well as the compensation award should have been apportioned two thirds from the employer and one third from the [Second Injury] fund.
In Northwest Carriers v. Industrial Commission, Utah, 639 P.2d 138 (1981), the employee Camp suffered a sixty-five percent loss of bodily function in a fall from scaffolding. In addition, he had a three percent loss attributable to psychiatric complications from conditions predating the accident. We held the Second Injury Fund responsible for 3/68 of Camp’s benefits. In Paoli v. Cottonwood Hospital, Utah, 656 P.2d 420 (1982), and McPhie v. United States Steel, Utah, 551 P.2d 504 (1976), we had the opposite situation. The prior permanent impairment greatly exceeded the impairment attributable to the second accident. In all of these cases, it was either discussed or it was implicit in the decision that the preexisting incapacity, when combined with the incapacity from the second injury, made the total incapacity “substantially greater” than it would have been without the prior incapacity. None of our cases have required or even suggested that the incapacity inflicted by the second injury had to be “substantially greater” than the preexisting impairment. The statute does not contain that requirement.1 All that is required is that the second injury be one for which compensation and medical care is provided by our statutes.
Since Chavez’s pre-1977 incapacity was thirty-three percent, it clearly made his total incapacity following the 1977 accident “substantially greater.” The case is remanded to the Industrial Commission to make an award of permanent partial benefits from the Second Injury Fund to Chavez on account of his preexisting impairment, less any portion for which he may have been already compensated, Paoli v. Cottonwood Hospital, supra, and to order the Second Injury Fund to reimburse Kaiser for its proportionate share of benefits already paid Chavez by Kaiser. No costs on appeal are awarded,
STEWART and DURHAM, J., concur.. In 1981, section 35-1-69 was amended to require that the percentage of permanent physical impairment attributable to the second injury be ten percent or greater. However, the rights and liabilities of the parties are determined on the basis of the law as it existed at the time of the occurrence, which in the instant case was 1977. Utah Construction Co. v. Matheson, Utah, 534 P.2d 1238 (1975); Okland Construction Co. v. Industrial Commission, Utah, 520 P.2d 208 (1974).