The dispositive issue presented for our review is whether a compensation claim for a work-related injury sustained in a car collision is barred because it was not filed within one year after the date of the accident. We answer in the affirmative.
THE ANATOMY OF LITIGATION
Melvin McDonald [worker] was injured on October 7, 1977 in an on-the-job automobile accident while working for Time-DC, Incorporated. The same day the worker reported the accident to his company. Three days later he went to a hospital emergency room and received a prescription for muscle relaxants. Some five weeks after the accident he noticed a “coldness” in his feet. He met with a doctor about the condition which persisted throughout 1978.
The worker was hospitalized on January 2, 1979 and diagnosed as suffering from a loss of blood circulation below both knees. It is at this time, he testified, that he first realized the causal link between the car accident and the injury to his circulatory system.
The worker filed a compensation claim on March 6,1979, alleging that he suffered permanent injuries from the October 1977 accident. The trial judge concluded the claim was barred by the applicable compensation law’s limitation, because it was filed more than one year after the accident. 85 O.S.1971 § 43.1 A three-judge review panel affirmed the denial of compensation. *1254The Court of Appeals vacated the order, holding that in a “single-event injury”2 the one-year limitation period of § 43 does not begin to run until a claimant is aware or should be aware of the full extent of his work-related injury.3
We grant certiorari to revisit the question when statutory time to filé a workers’ compensation claim for a single-event injury begins to run.
I
THE STATUTORY TIME TO FILE A WORKERS’ COMPENSATION CLAIM FOR A SINGLE-EVENT INJURY BEGINS TO RUN FROM THE DATE OF THE ACCIDENT
The worker argues the limitation period did not begin to run until he “discovered” the full extent of his injury.4 We must recede from this view.
In Stillwater Floral Company v. Murray,5 a single-event injury case, this court held that the terms of 85 O.S.1961 § 43 (the version then under review) barred a worker’s compensation claim because it was not filed within one year after an injury. There, we said an injury is inflicted at the time of the accident, not when its full extent is first noted.6 More specifically, the court’s construction of the compensation law was that it
“has no provision [relative to a single-event injury] for computing the limitation period from the time disability develops.... [and that the court is] ‘not free, under the guise of construction, to amend the statute by inserting therein before the word ‘injury’ the word ‘com-pensable’ so as to make ‘injury’ read as if it were ‘disability’.’” [Emphasis added.]7
Stillwater Floral does not stand alone on this point; we have repeatedly rejected the argument that the one-year limitation begins to run when the disability occasioned by an accidental injury becomes fully apparent.8
In support of his “awareness” argument, the worker relies on Munsingwear, Inc. v. Tullis, a cumulative-effect injury case, *1255where we held the limitation period begins to run when the worker is aware, or should be aware, of some defect that is causally connected with the job.9 There we observed:
“Stillwater Floral Company v. Murray ... suggests the injury need not be one capable of full medical evaluation, but an injury with the accident sufficient for the workman to be aware, or should be aware, of some defect or some ill effect, produced thereby.” [Emphasis added.]10
The worker misinterprets the teaching of Munsingwear. Our ruling in that case is rested on the language of § 43 then in effect11 and on the character of the worker’s injury. Munsingwear was not intended to be a blank endorsement of an awareness doctrine similar to the “discovery rule”,12 which applies in general civil litigation.13 Its teaching was but an adaptation of the Stillwater Floral principle that the § 43 one-year limitation begins to run at the time of the accidental injury which is *1256known or should have been known, not from the time the full extent of the worker’s disability becomes manifest.
Because Stillwater Floral defines “injury” by reference to the “time of the accident,” 14 it was necessary in Munsingwear to settle on the exact point in time when repeated exposure to noxious smoke will culminate in an accident. The essence of the Munsingwear reasoning is that the cumulative effect of repeated microtrauma or exposure to hazardous conditions does not become an “accident” until a worker is aware, or should be aware, of a “defect” that is causally connected with his job. This conclusion accommodates the peculiar characteristic of a cumulative-effect injury —a phenomenon that occurs imperceptibly and unexpectedly.15 Conversely, where there is a single event (like an automobile accident), the injurious occurrence itself is far from latent.16 Some ill effect, however trivial, will be or should be recognizable immediately.17
When the worker knows that a single-event industrial accident has taken place, he (or she) is charged with awareness of its occurrence. This, in turn, raises legal awareness of compensable injury, present or potential. Awareness of potential injury, much like that of immediate harm, imposes a duty upon the worker to protect his rights by filing a timely claim.
Properly analyzed, Stillwater Floral and Munsingwear apply the same test under different factual scenarios. The former teaches the test’s proper application where a worker is injured in a single, finite accident. By the latter the same rule is refitted for use limited to cumulative-effect injuries.18
Although § 43 has been amended three times since Stillwater Floral, our lawmaking body has not altered the statute’s substantive language insofar as it regulates the time to bring claims for single-event injuries.19 The legislature must hence be *1257deemed to have ratified our prior interpretation of § 43.20
In sum, the language of § 43 clearly militates against a construction that would allow engrafting a tort-like discovery rule. Rather, the time to file a claim for a single-event injury runs from the time the worker is charged with legal awareness of the present or potential ill effect, not from the onset or manifestation of disability or impairment. Our current statutory scheme makes a similar rule applicable to claimants who seek compensation for most cumulative-effect injuries.21 Only for asbestosis, silicosis or exposure to nuclear radiation does the limitation period now in effect begin to run from the date of manifestation. 85 O.S.Supp.1986 § 43(A). The cited enactment’s restriction operates as an explicit exception from the general regime for application to some forms of cumulative-effect injuries. The legislative enumeration of compensable harms singled out from others clearly prohibits a judicial extension of similar exceptions both to single-event or to other kinds of cumulative-effect injuries, regardless of apparent hardship or inconvenience.22
II
A DICHOTOMOUS DIVISION OF CLAIMANTS BASED ON THE CHARACTER OF INJURY SUSTAINED IN AN INDUSTRIAL ACCIDENT RESTS ON LEGITIMATE STATE INTERESTS AND DOES NOT OFFEND CONSTITUTIONAL RESTRICTIONS ON THE GOVERNMENTAL USE OF CLASSIFICATIONS
Single-event and cumulative-effect injuries bear distinctive characteristics which require different treatment. Recognition of these separate classes is necessary for fair application of § 43’s one-year (now two-year) limitation. It is hence rationally related to legitimate state interests in orderly adjudication of claims and in judicial economy. There is here no violation of the U.S. Constitution’s Equal Protection Clause of the 14th Amendment.23
*1258Ill
THE WORKER’S COMPENSATION CLAIM IS BARRED FOR FAILURE TO FILE A PROCEEDING WITHIN ONE YEAR AFTER THE DATE OF THE ACCIDENT
The worker suffered injuries in an automobile collision. His claim is based on a single-event injury and, hence, can escape legislative extinguishment only if a proceeding was brought within one year (now a two-year interval) of the date the accident occurred. This is the very date the worker first became charged with legal awareness of some defect, or ill effect, from the job-related occurrence. His lack of knowledge — at that point in time — of the full extent of his disability is legally irrelevant.
Because the record clearly demonstrates the worker was immediately aware of his October 1977 accident, he was also legally aware at that time of present or potential harm. Consequently, the worker had a duty to file his claim within one year of that date. His March 1979 claim, filed more than one year after the accident's occurrence, is barred by § 43.
CERTIORARI IS GRANTED, THE COURT OF APPEALS’ OPINION IS VACATED AND THE ORDER OF THE REVIEW PANEL OF THE WORKERS’ COMPENSATION COURT IS SUSTAINED.
HARGRAVE, C.J., and HODGES, LAVENDER and SIMMS, JJ., concur. DOOLIN, ALMA WILSON and SUMMERS, JJ., dissent. KAUGER, J., dissents by reason of stare decisis.. The terms of 85 O.S.1971 § 43 — the statute in effect at the time of the worker's car accident in which the injuries are claimed to have been sustained — provided in part:
“The right to claim compensation under this Act shall be forever barred unless within one (1) year after the injury or death, a claim for compensation thereunder shall be filed with the Commission_ Provided further, however, with respect to radiation disease ... the right to claim compensation under this Act shall he forever barred unless a claim is filed within one (1) year after the last hazardous exposure or within one (1) year after the disease first becomes manifest by a symptom or condition from which one learned in medicine could with reasonable accuracy diagnose this specific disease. * * *” [Emphasisadd-ed.]
*1254Section 43 was later amended in 1977, 1985 and 1986 [Okl.Sess.L.1977, Ch. 234, § 1, eff. July 1, 1978; Okl.Sess.L.1985, Ch. 266, § 4, eff. Nov. 1, 1985; and Okl.Sess.L.1986, Ch. 222, § 17, eff. Nov. 1, 1986].
. An accidental injury may result either from one particular event — a "single-event injury"— or from the cumulative effect of repeated micro-trauma occurring over an extended period of time — a "cumulative-effect injury." Munsingwear, Inc. v. Tullis, Okl., 557 P.2d 899, 903 [1976]; Macklanburg-Duncan Company v. Edwards, Okl., 311 P.2d 250 [1957] (syllabus ¶ 1).
. The Court of Appeals held that there can be no injury of a compensable nature until the victim is aware of an injury and there can be no notice requirement under the Workers’ Compensation Act until the date of first discovery or awareness of an injury.
. The worker also contends the trial judge erred when he concluded that the trial tribunal was "without jurisdiction” to entertain his claim. Although the worker is technically correct— since § 43 is a limitation extinguishing the remedy rather than affecting the right, Munsingwear, Inc. v. Tullis, supra note 2 at 901—his argument is at best academic. Suffice it to say the trial tribunal has the authority to decide whether a claim was timely brought or is barred by § 43.
. Okl., 380 P.2d 694, 697 [1963]. In Stillwater Floral the worker was injured when a gas explosion caused a sheet metal object to strike him in the head. Two months after the accident he began suffering from headaches and a year and a half later from blackout spells. He was then diagnosed as having a brain lesion caused by the blow to his head.
. Stillwater Floral Company v. Murray, supra note 5 at 696.
. Stillwater Floral Company v. Murray, supra note 5 at 696, quoting Pillsbury v. United Engineering Co., 342 U.S. 197, 199, 72 S.Ct. 223, 224, 96 L.Ed. 225 [1952].
. In support of this argument claimants usually have relied upon Brown & Root v. Dunkelberger, 196 Okl. 116, 162 P.2d 1018, 1019 [1945]. There, the court stated in syllabus ¶2: “Under the provisions of the Workmen’s Compensation Law ... the statute of limitations does not begin to run ... until the disability arising from such accidental injury becomes apparent." See also Swift & Co. v. State Industrial Commission, 161 Okl. 132, 17 P.2d 435 [1932] (syllabus); Bartlett-*1255Collins Co. v. Roach, 180 Okl. 521, 71 P.2d 489-490 [1937] (syllabus ¶ 1).
We simply note today that these cases, insofar as they support such a rule, were expressly overruled in Tulsa Hotel v. Sparks, 200 Okl. 636, 198 P.2d 652, 655 [1948]. For other single-accident cases where we explicitly rejected arguments grounded on Brown & Root, supra, see Swafford v. Schoeb, Okl., 359 P.2d 584, 586 [1961]; Evans v. Tulsa City Lines, Okl., 290 P.2d 126, 127 [1955]; Caouette v. American Airlines, Okl., 276 P.2d 753, 754 [1954]; Cooper v. Oklahoma Hotel Bldg. Co., 205 Okl. 337, 237 P.2d 875, 877 [1951]; York v. State Industrial Commission, 201 Okl. 636, 208 P.2d 563, 565 [1949].
. Munsingwear, Inc. v. Tullis, supra note 2. There the claimant, a seamstress, suffered a work-related disability from repeated exposure to smoke caused by a hot needle on fabric. The worker here also relies upon American Airlines, Inc. v. McCombs, Okl., 555 P.2d 1028 [1976]; Eaton v. Herman Van Noy Drilling, Okl., 637 P.2d 1249 [1981]; Esmark/Vickers Petroleum v. McBride, Okl., 570 P.2d 951 [1977]; Wilson Foods Corp. v. Noble, Okl.App., 613 P.2d 485 [1980]—each case involves a disability from the cumulative effect of repeated exposure to some harmful element in the work environment.
. Munsingwear, Inc. v. Tullis, supra note 2 at 903.
. Unlike later versions, § 43’s 1971 version did not explicitly differentiate between single-event injuries and injuries resulting from the cumulative effect of repeated exposure to trauma or hazardous working conditions. Instead, it used a single term — injury—to encompass both classes of accidental injury.
. The “discovery rule” allows limitations in tort cases to be tolled until the injured party knows or, in the exercise of reasonable diligence, should have known of the injury. Its presence in our jurisprudence is a fairly recent common-law development. See Reynolds v. Porter, Okl., 760 P.2d 816, 820, n. 8 [1988]. Actionable tort claims favorably affected by Oklahoma’s tort discovery rule include medical malpractice claims (Seitz v. Jones, Okl., 370 P.2d 300, 302 [1962]); claims generated by pollution of a stream (Continental Oil Co. v. Williams, 207 Okl. 501, 250 P.2d 439, 441 [1952]); claims for damage to realty (Harper-Turner Oil Company v. Bridge, Okl., 311 P.2d 947, 950 [1957]); and claims for negligent exposure to an infectious disease with latent symptoms (Sloan v. Canadian Valley Animal Clinic, Inc., Okl.App., 719 P.2d 474 [1986]).
.Although the awareness rule that is applied to a cumulative-effect injury may in some instances have the same practical effect as a tort discovery rule (Daugherty v. Farmers Co-op. Ass'n, Okl., 689 P.2d 947, 950 [1984]), it would be improper to entertain the notion that an awareness or "discovery rule” similar to that currently followed in tort liability litigation can be adopted for compensation claims. The legislatively-prescribed regime of limitations which governs claims for compensation of workers injured on the job is completely self-containing. Past attempts to engraft upon this statutory body conceptual transplants from the common law or to borrow from enactments applicable in district court litigation have been consistently condemned as impermissible. The “Workmen’s Compensation Law is an act of the Legislature complete in itself.” Indian Territory Illuminating Oil Co. v. Crown, 158 Okl. 51, 12 P.2d 689, 692 [1932], "[T]he general statute of limitations in the Civil Code which enables a minor in certain cases to bring an action at any time within a year after he reaches ... majority has ... [no] application to claims arising under the Workmen’s Compensation Law.” Indian Territory Illuminating Oil Co. v. Crown, supra, 12 P.2d at 691. See also United Brick & Tile Company v. Roy, Okl., 356 P.2d 107, 109 [1960]; Smith v. State Industrial Commission, 182 Okl. 433, 78 P.2d 288, 289 [1938].
The Munsingwear test (infra note 18) is not to be perceived as elevating “awareness” to actual knowledge that a worker’s condition is medically related to some work-connected activity. Our recent opinion in Coy v. Dover Corporation, Okl., 773 P.2d 745 [1989] teaches that expert advice about the etiology of a cumulative-effect injury is not a sine qua non for triggering the applicable limitation period.
. Stillwater Floral Company v. Murray, supra note 5 at 696.
. Munsingwear, Inc. v. Tullis, supra note 2 at 903, citing Macklanburg-Duncan Company v. Edwards, supra note 2.
. Stillwater Floral Company v. Murray, supra note 5 at 697.
. We stated in Stillwater Floral v. Murray, supra note 5 at 697:
"The mere fact that claimant could not, from a medical standpoint, evaluate the full extent of his injury (however trivial it may have seemed) until much later, did not operate to toll, or arrest, the limitation period.”
We note that in this case the worker testified he went to an emergency room three days after the automobile accident, presumably because he was aware of some ill effect caused by the accident.
. To limit the scope of its holding, the court said in Munsingwear, Inc. v. Tullis, supra note 2 at 903:
"Under the circumstances of a cumulative effect accident, the accidental injury, which accompanies the accident, occurs (l) at the time of claimant’s awareness, or discovery, of a "defect" or "ill effect” caused to the claimant; and (2) at the time of his awareness that the effect is causally connected with his job....
It is then, the accident has occurred and carries with it the accompanying injury. At that point in time, the cumulative accident is no different [from] ... the single event accident from a limitation issue.” [Emphasis added.]
See also, Daugherty v. Farmers Co-op. Ass’n, supra note. 13 at 950, where we note the rule’s limited application to cumulative-effect injury only.
The Munsingwear two-prong awareness doctrine, recently revisited in Coy v. Dover Corporation, supra note 13, is to be viewed as governed by an objective ("reasonable man”) standard for both parts of the test.
. In 1985 the time period for filing a claim was enlarged from one to two years. (See Okl.Sess. 1985, Ch. 266, § 4, eff. Nov. 1, 1985). The language pertinent here was not changed by § 43’s latest amendment in 1986 (Okl.Sess.1986, Ch. 222, § 17, eff. Nov. 1, 1986). The fact that § 43’s limitation period for a single-event injury has been enlarged is not significant here because the worker’s October 7, 1977 injury occurred prior to those amendments. Absent express or implied legislative intent to the contrary, an amendment to the Workers’ Compensation Act is inapplicable to injuries sustained prior to the enactment’s effective date. See Weber v. Armco, Inc., Okl., 663 P.2d 1221, 1227 [1983]. There is no indication of any such intent and none has been advanced by the parties.
*1257In comparison to single-event injuries, § 43 at one time expressly permitted a worker suffering from any cumulative-effect injury to file a claim within eighteen months after the last hazardous exposure or after the disease first became manifest by a symptom or condition. See 85 O.S. Supp.1977 § 43. Even this rule’s application has now been confined solely to enumerated illnesses; claims for all other cumulative-effect injuries must now be filed within two years after the date of the last trauma or hazardous exposure — without regard to when symptoms became manifest. See 85 O.S.Supp.1986 § 43, infra, note 21.
. See Larkin v. Hiittenmeyer, 195 Okl. 669, 161 P.2d 749, 750-751 [1945], where we stated that it must be assumed the legislature is cognizant of judicial interpretations of statutes; failure to later amend a statutory provision is tantamount to legislative acquiescence, ratification and approval of extant judicial construction. In Lekan v. P & L Fire Protection Co., Okl., 609 P.2d 1289, 1292 [1980], it is stated: "Legislative familiarity with extant judicial construction of statutes in the process of being amended is presumed. Unless a contrary intent clearly appears or is plainly expressed, the terms of amendatory acts which retain the same, or not substantially dissimilar, portions of provisions formerly in force will be accorded the construction identical to that placed upon them by preexisting case law.” See also Garrison v. State, Okl., 420 P.2d 474, 477 [1966]; Huff v. State, Okl., 764 P.2d 183, 185 [1988].
. The present version of § 43, as amended in 1986 (Okl.Sess.L.1986, Ch. 222, § 17, eff. Nov. 1, 1986), provides in pertinent part:
"... with respect to disease or injury caused by repeated trauma causally connected with employment, a claim may be filed within two (2) years of the date of last trauma or hazardous exposure_” See also Coy v. Dover Corporation, supra note 13.
. Cummings v. Board of Education, 190 Okl. 533, 125 P.2d 989, 993 [1942]; Lake v. Lietch, Okl., 550 P.2d 935, 937 [1976].
. Because these two classifications burden neither a fundamental interest nor a suspect class, the rational basis test must govern their constitutional validity. Under this standard, a statute will be upheld as free of infirmity unless the varying treatment of the different groups or persons is so unrelated to the achievement of any combination of legitimate state purposes that one can only conclude the classifications are irrational. Vance v. Bradley, 440 U.S. 93, 97, 99 S.Ct. 939, 942-943, 59 L.Ed.2d 171 [1979]; Pennell v. City of San Jose, 485 U.S. 1, 108 S.Ct. 849, 859, 99 L.Ed.2d 1 [1988]; see also Black v. Ball Janitorial Service, Inc., Okl., 730 P.2d 510, 513, n. 8 [1986].