Opinion by
LARRY JOPLIN, Presiding Judge.¶ 1 Petitioners Keco, Inc. (Employer) and Medmarc Insurance Company (Medmarc, or collectively, Petitioners) seek review' of orders of the trial court holding Medmarc solely responsible for cumulative trauma injuries to the left hand/thumb of Respondent Carroll Hayward (Claimant) and dismissing Respondent Villanova Insurance Company (Villano-va), predecessor in interest to the OMahoma Property and Casualty Insurance Guaranty Association (OPCIGA). In this proceeding, Petitioners assert the trial court erred as a matter of both fact and law in dismissing Villanova and holding Medmarc solely liable for Claimant’s injuries under 85 O.S. § 11(B)(5). Having reviewed the record, however, we discern no error of law or fact. Accordingly, the order of the trial court is sustained.
¶ 2 Claimant worked for Employer from August 1971 through August 2002. By joint petition in September 1997, Claimant obtained an award of benefits for an injury to his right hand while working for Employer.
¶ 3 In October 2003, Claimant commenced an action against Employer to recover benefits for a cumulative trauma injury to his left hand. As respondents, Claimant named Employer, Villanova and Medmarc; Villanova (whose liabilities were subsequently assumed by OPCIGA) was Employer’s workers’ compensation insurer from March 2000 through March 1, 2002, and Medmarc was Employer’s insurer from March 1, 2002 to March 1, 2003.
¶ 4 At trial, Claimant asserted that he did not know that the injury to his left hand/thumb was job-related until examined in April 2000, and the report of the examining physician referred to March 13, 2000 as the date of injury. Claimant testified that he was last hazardously exposed to the cumulative-trauma-dealing conditions of his employment with Employer on August 29, 2002 when he resigned. Claimant also testified that he submitted to surgery on his left thumb in July 2003; that he was released from medical treatment of his left thumb in October 2003; and that, due to the injury and treatment of his left thumb, he did not work from August 2002 until January 2004 when he accepted other employment not requiring the painful use of his left thumb.
¶ 5 Claimant admitted that, at the time of the joint petition settlement in September 1997, he was experiencing some left thumb pain. Claimant, at one point, asserted that the'1997 joint petition covered only the injury to his right hand, but later admitted that, on the joint petition record, he acknowledged the award was to cover any injury to either hand.
*52¶ 6 Claimant offered, and the trial court admitted, medical evidence in support of his claim. Medmarc and OPCIGA offered the records of the joint petition settlement, arguing the 1997 settlement cut off any right to benefits for left hand injury absent proof of a subsequent aggravation of the left hand injury, but that the parties had offered no testimony or evidence of such an aggravation.
¶ 7 Medmarc also offered medical evidence argued to show Claimant’s awareness of the injury to his left thumb at the time of settlement in 1997, as to render OPCIGA solely liable for Claimant’s benefits which had then accrued during Villanova’s period of workers’ compensation insurance coverage. Alternatively, Medmarc demanded apportionment of liability between it and OPCIGA, arguing that, because Claimant was aware of his left hand injury prior to enactment of § 11(b)(5) in 2001, his right to benefits then became fixed, and that the law in effect at the time permitted apportionment.
¶ 8 OPCIGA offered medical evidence, and argued the testimony and evidence clearly demonstrated Claimant’s last hazardous exposure to the trauma-dealing conditions of the employment for more than one-hundred twenty days during Medmarc’s coverage period. So, said OPCIGA, Medmarc was solely responsible for Claimant’s benefits under § 11(b)(5).
¶ 9 On consideration of the testimony, evidence and argument, the trial court found: (1) the 1997 Joint Petition adjudicated only the injury to Claimant’s right hand, not to his left thumb; (2) “on March 13, 2000, [CJlaim-ant became aware [he] had sustained accidental personal injury as a result of cumulative trauma to the Thumb of the left hand arising out of and in the course of [CJlaim-ant’s employment” with Employer; and (3) “Claimant’s last injurious exposure to said trauma was on August 29, 2002.” On these findings, the trial court concluded:
THAT ... all liability for the alleged injury herein is found against MEDMARC CASUALTY INSURANCE COMPANY herein pursuant to 85 O.S. [§ ]11(B)(5). Although the legal awareness predated the OCTOBER 23, 2001 change in the statute, the cumulative trauma injury continued beyond that date until the [Cjlaimant’s AUGUST 29, 2002 last date of exposure. His exposure from MARCH 2000 until AUGUST 29, 2002 did not change and the injury continued to occur during this time period.
(Emphasis original.) The trial court consequently ordered Medmarc to pay Claimant accrued benefits for 13 weeks of temporary total disability, 25 weeks of permanent partial disability, as well as “all reasonable and necessary medical expenses incurred by [C]aimant [Claimant] as a result of said injury.” By supplemental order, the trial court subsequently held “Villanova Insurance Company/Oklahoma Property & Casualty Insurance Guaranty Fund is not liable/responsible for any benefits herein and is hereby dismissed with prejudice.”
¶ 10 Petitioners now seek review in this Court, but raise no challenge to the trial court’s adjudication of Claimant’s compensa-ble injuries. Consequently, the only question to be resolved concerns who, as between OPCIGA and Medmarc, will bear responsibility for payment of Claimant’s benefits.
¶ 11 In three substantive propositions, Petitioners argue that the date of Claimant’s “awareness” of the job-related cumulative trauma injury to his left thumb determines the date of injury, and both Claimant’s right to benefits and an insurer’s obligation to pay are consequently fixed under the law in effect at the time of the injury. See, e.g., Selfridge v. Multiple Injury Trust Fund, 2002 OK CIV APP 5, ¶ 4, 42 P.3d 1240, 1241; Rankin v. Ford Motor Co., 1996 OK 94, ¶¶ 9, 10, 12, 925 P.2d 39, 40, 41; Parks v. Flint Steel, 1988 OK 64, ¶¶ 12-13, 755 P.2d 680, 683; Munsingwear v. Tullis, 1976 OK 187, ¶ 13, 557 P.2d 899, 903. So, say Petitioners, because § 11(B)(5) affects a substantive change in the law governing which of several insurers are obligated to pay benefits, that section cannot be applied retroactively to alter liability for an injury occurring before its effective date. Sudbury v. Deterding, 2001 OK 10, ¶ 19, 19 P.3d 856, 860; Knott v. Halliburton Svcs., 1988 OK 29, ¶ 4, 752 P.2d 812, 813-814.
*53¶ 12 In response, OPCIGA argues that, since the 1985 amendment to 85 O.S. § 43(A), which fixed the date of last hazardous exposure as the operative date for statute of limitations purposes, the date of a claimant’s “awareness” of his cumulative-trauma injury is irrelevant.1 B.F. Goodrich v. Williams, 1988 OK 62, ¶¶ 6, 7, 755 P.2d 676, 678. So, says OPCIGA, notwithstanding Claimant’s “awareness” in 2000, because Claimant was continuously exposed to the same cumulative-trauma-injury dealing hazards of the employment until August 2003, Claimant’s “inchoate” claim did not accrue until filed in October 2003, two years after the October 2001 effective date of § 11(B)(5), and that the trial court properly applied that section. Alternatively, it argues, the Legislature’s 1985 amendment to § 43, dispensing with the “awareness” doctrine for statute of limitations purposes, is consistent with § 11(B)(5), which imposes liability without regard to “awareness,” and the Legislature may properly enact legislation applicable to claims arising before the effective date where the legislative intent is so clearly expressed. See also, Norton v. C.P. Blouin, Inc., 511 A.2d 1056, 1062 (Me.1986).
¶ 13 Prior to enactment of § 11(B)(5), the Court of Civil Appeals recognized that, where a claimant suffered cumulative trauma injuries in successive employments, or while insured by successive insurers, apportionment of liability for the claimant’s benefits was proper. See, Ball-Incon Glass v. Adams, 1995 OK CIV APP 16, 894 P.2d 439; Kerr Glass Co. v. Wilson, 1994 OK CIV APP 69, 880 P.2d 414; Lummus Const. v. Vancourt, 1992 OK CIV APP 113, 838 P.2d 43; Pauley v. Lummus Const., 1992 OK CIV APP 96, 836 P.2d 692. However, effective October 23, 2001, the Oklahoma Legislature amended 85 O.S. § 11, and subsection (B)(5) now provides:
Where compensation is payable for an injury resulting from cumulative trauma, the last employer in whose employment the employee was last injuriously exposed to the trauma during a period of at least ninety (90) days or more, and the insurance carrier, if any, on the risk when the employee was last so exposed under such employer, shall alone be liable therefor, without right to contribution from any pri- or employer or insurance carrier....
¶ 14 By enactment of § 11(B)(5), “the Legislature intended to make the last exposure doctrine apply to cumulative trauma cases, both for determination of the date of injury and for the determination of the liable employer in cases of multiple employers.” Celestica Inc. v. Hines, 2004 OK CIV APP 22, ¶ 9, 86 P.3d 1095, 1098. By force of this section, where a claimant suffers a cumulative trauma injury in the course of his or her employment for a single employer, and is last injuriously exposed to the trauma “during a period of at least ninety (90) days,” “then ‘the insurance carrier ... on the risk when the employee was last so exposed ... shall alone be liable, therefor, without right to contribution from any prior ... insurance carrier.’ ” OCT Equipment, Inc. v. Ferrell, 2005 OK CIV APP 36, ¶ 7, 114 P.3d 479, 481, cert. den., 2005 OK 38. Application of § 11(B)(5) is not impermissibly retroactive as to an insurer who assumed the risk after that section’s effective date. Celestica Inc., 2004 OK CIV APP 22, ¶ 10, 86 P.3d at 1098.2
¶ 15 In the present case, it is undisputed that Claimant suffered a cumulative trauma injury while working for Employer, and, although aware of the injury in March 2000, was last exposed to the cumulative trauma dealing hazards of the employment in August 2002. From and after the effective date of § 11(B)(5), Claimant’s “awareness” of his cumulative trauma injury was irrelevant to the determination of the “date of injury,” by force of that section, determined solely by *54reference to the date of last exposure. Celestica Inc., 2004 OK CIV APP 22, ¶ 9, 86 P.3d at 1098.
¶ 16 Medmarc assumed the risk on or about March 1, 2002, over a year after the effective date of § 11(B)(5), and was charged with notice of the law then in effect. Section 11(B)(5), at that time, imposed liability solely on “the insurance carrier ... on the risk when the employee was last so exposed [during a period of at least ninety (90) days or more,] ... without right to contribution from any prior ... insurance carrier.” Medmarc has suffered no increased obligation to pay greater benefits than when it assumed the risk.
¶ 17 We hold the trial court did not err as matter of fact or law in holding Medmarc solely liable for Claimant’s cumulative trauma injury to his left thumb. The order of the trial court is therefore SUSTAINED.
BUETTNER, C.J., concurs; and HANSEN, J., dissents with separate opinion.. Except for purposes of determining rate of compensation. See, Rankin, 1996 OK 94, ¶¶ 10, 12, 925 P.2d at 40, 41.
. "... Celestica took over the plant after the effective date of the statute and was charged with notice of the law in effect at that time. Additionally, Celestica has failed to cite any authority to support its argument that the last exposure rule is unconstitutional. Indeed, the last exposure doctrine, in occupational disease cases, has long been upheld. See Parks v. Flint Steel Corp., 1988 OK 64, 755 P.2d 680.... Accordingly, we find no support for Celestica’s argument that the last exposure rule is unconstitutional."