Opinion by JUDGE METZGER.

In this workmen's compensation case, claimant, Johnnie C. Irwin, seeks review of a final order of the Industrial Commission denying and dismissing her claim for benefits for injuries sustained during an unexplained fall while on the job. We affirm.

The pertinent facts were stipulated by the parties. On October 22, 1980, claimant began working as a security guard trainee for Stanley Smith Security, Inc. On that day, after she had been on the job approximately three and one-half hours in the lobby of the building to which she was assigned, "suddenly, without warning, and for reasons which are as yet unknown, she fainted and fell to the floor." She was treated for injuries to her low back, coccyx, neck, and left leg. At the time the stipulation was filed in March 1983, claimant had been unable to return to work since her fall and her present condition included numbness in her left hand and her entire left side, pain in her lower back, and weakness and tingling in her left leg. The stipulation also indicated that, prior to the incident in the instant case, claimant had a history of attacks wherein she would lose consciousness or black out.

The hearing officer found that claimant had suffered a compensable injury. Although finding that the reasons for claimant's fall were "as yet unknown," the hearing officer concluded that claimant's low back injuries were proximately caused by her passing out and falling, and that these injuries arose out of, and were in the course of, her employment and were not intentionally self-inflicted.

The Commission reversed, finding that claimant had not met her burden of proof. Relying on Finn v. Industrial Commission, 165 Colo. 106, 437 P.2d 542 (1968), the Commission concluded that "the case is one of an unexplained fall and possibly the resulting injury from the fall, but in which there is not substantial and competent evidence to establish that the injury or fall arose out of and in the course of employment."

On review, claimant first contends that respondents' petition for review of the hearing officer's order was insufficient because it failed to "specify in detail the particular errors and objections," as required by § 8-53-106(3), C.R.S. (now § 8-53-111(1), C.R.S. (1983 Cum. Supp.)). Because no objection was raised by claimant until after the Commission entered its order, we decline to address this issue.

Claimant also contends, in substance, that the Commission erred in concluding that her injury did not arise out of and in the course of her employment. We disagree.

Clearly, claimant fell in the course of her employment. See Deterts v. Times Publishing Co., 38 Colo. App. 48, 552 P.2d 1033 (1976). The critical issue is whether claimant's injury arose out of her employment.

For an injury to arise out of employment, there must be a causal connection between the duties of employment and the injury suffered. See Finn v. Industrial Commission, supra; Deterts v. Times Publishing Co., supra. However, for an injury to arise out of employment it need not always be a direct result of an employment-related cause; e.g., a falling hammer or exposure to harmful gases or liquids. Rather, injuries also have been held to arise out of employment where, although the direct cause of the injury is not employment related, an employee's work placed him in a position in which he ultimately sustained an injury.

This positional-risk doctrine was first developed in Colorado in Aetna Life Insurance Co. v. Industrial Commission, 81 Colo. 233, 254 P. 995 (1927). See 1 A. Larson, Workmen's Compensation Law § 8.12 at 3-22 through 3-24 (1983). In Aetna, a farm hand, while in the course of his employment, was killed when he was struck by lightning. The positional-risk doctrine, as distilled from Aetna, provides that:

"[I]n cases involving injuries of an origin not common to a particular type of employment, if an employee's work positions him where he was when injured, and if it is demonstrated that his injury would not have occurred but for that fact, the required causal connection between the employment and the injury has been established." Kitchens v. Department of Labor Employment, 29 Colo. App. 374, 486 P.2d 474 (1971) (emphasis in original).

Since Aetna, the positional-risk doctrine has been applied to allow compensation where a direct employment cause is lacking. See London Guarantee Accident Co. v. McCoy, 97 Colo. 13, 45 P.2d 900 (1935) (employee murdered by insane man while in course of employment); Kitchens v. Department of Labor Employment, supra (employee injured when co-employee accidentally discharged hunting rifle).

In contrast, in Velasquez v. Industrial Commission, 41 Colo. App. 201, 581 P.2d 748 (1978), this court upheld the denial of compensation to two claimants who were shot by a perturbed co-employee who believed that claimants were responsible for making obscene telephone calls to his wife. In applying the positional-risk doctrine, the court noted that although the claimants were injured at work, they failed to establish the requisite causal connection because "they failed to establish that their injuries would not have occurred but for the fact that their employment positioned them where they were when injured." That is, the shooting could have happened wherever and whenever the co-employee found the claimants.

Here, since the facts are undisputed, we are not bound by the Commission's legal conclusions. See Deterts v. Times Publishing Co., supra. As noted above, the absence of a direct employment cause for claimant's fall does not preclude recovery. However, claimant bore the burden of proof to bring herself within the parameters of the test stated in Kitchens v. Department of Labor Employment, supra. See Velasquez v. Industrial Commission, supra. Although the parties stipulated that the reasons for the fall were as yet unknown, the parties also stipulated that claimant had a history of blacking out and losing consciousness. In light of this history, claimant failed to establish the "but for" requirement, since her fall could have happened at any other time or place. See Velasquez v. Industrial Commission, supra. Accordingly, the Commission correctly concluded that claimant had failed to establish that her injuries arose out of her employment.

We leave open for determination at a further time the question whether a truly unexplained fall, with no exigent circumstances present, arises out of employment and is compensable. See generally 1 A. Larson, supra, § 10.31 at n. 71. But cf. Finn v. Industrial Commission, supra.

The order is affirmed.

JUDGE KELLY concurs.

JUDGE TURSI dissents.