Shaw Construction, Inc., an underground utilities construction company, petitions for review of an order of the Occupational Safety and Health Review Commission dated July 22, 1975, which held that Shaw committed two serious violations of regulations defining safety standards for trenching operations. In May of 1973, Shaw was engaged in lowering a telephone conduit which entailed, among other things, the construction of a trench nine feet deep, five feet wide, and twenty feet long.

The Secretary of Labor cited Shaw for a number of alleged violations of the Occupational Safety and Health Act of 1970, 29 U.S.C. § 651 et seq., in connection with this trench. The citations were contested, and the Commission administrative law judge who heard the case determined that two serious violations had occurred. The first involved Shaw’s failure to store excavated materials more than two feet from the edge of the trench, in violation of 29 C.F.R. § 1926.651(i)(l); ^[1] the second concerned improper shoring or sloping of the trench under 29 C.F.R: § 1926.652(c). ^[2] Following the issuance of the administrative law judge’s decision, Shaw petitioned for discretionary review by the full Commission pursuant to 29 U.S.C. § 661(i). ^[3] The Commission agreed[*1185] to dispose of the case, but due to the fact that one of its members had resigned and had not been replaced at the time Shaw’s petition was considered, only two commissioners participated in the review of the initial decision and order. Acting without a third member, the Commission affirmed the administrative law judge’s determinations as to each of the violations. Both commissioners concurred in affirming the first violation; the second was affirmed by a divided, one-to-one vote. A subsequent petition for rehearing after a third member had been appointed to the Commission was denied.

With regard to the first violation, Shaw conceded that excavated materials were stored within two feet of the edge of its trench, and argues only that the Commission erred in holding this to be a “serious” violation. Section 17(k) of the Occupational Safety and Health Act, 29 U.S.C. § 666(j), provides:

[A] serious violation shall be deemed to exist in a place of employment if there is a substantial probability that death or serious physical harm could result from a condition which exists ... in such place of employment unless the employer did not, and could not with the exercise of reasonable diligence, know of the presence of the violation.

(Emphasis added.) This provision has been construed as holding violations to be serious if they make possible an accident involving a substantial probability of death or serious physical harm. California Stevedore and Ballast Co. v. Occupational Safety and Health Review Commission, 9 Cir., 1975, 517 F.2d 986, 987-88. ^[4]

The administrative law judge found that Shaw had three-foot-high soil banks and large asphalt chunks adjacent to its trench, and that vibrations caused by nearby traffic and equipment in the trench might cause debris to fall into the trench. If this occurred, there would be a substantial probability that someone working in the trench would suffer serious injuries or death. There was thus substantial evidence to support the Commission’s 2-0 determination that a serious violation of section 1926.-651(i)(l) had occurred. We find no abuse of discretion in the Commission’s assessment of a $300 penalty against Shaw for this violation. See REA Express, Inc. v. Brennan, 2 Cir., 1974, 495 F.2d 822, 827; Brennan v. Occupational Safety and Health Review Commission, 8 Cir., 1973, 487 F.2d 438, 442-43; cf. Nadiak v. CAB, 5 Cir., 1962, 305 F.2d 588, 593, cert. denied, 372 U.S. 913, 83 S.Ct. 729, 9 L.Ed.2d 722 (1963). We therefore affirm the Commission’s order with regard to Shaw’s first violation.

The Commission erred, however, 'in disposing of the second violation with a one-to-one vote. Under the statutory provisions governing the Commission’s discretionary review of determinations made by Commission administrative law judges, no official action can be taken by the Commission without the affirmative vote of at least two of its members. ^[5] An affirmance sup[*1186] ported by only one vote does not comply with this statutory requirement and cannot stand. We accordingly remand the case to the Commission so that it may take appropriate official action in reviewing Shaw’s alleged sloping and shoring violation under section 1926.652(c). We intimate no view on the merits of Shaw’s petition in this regard.

AFFIRMED IN PART, REVERSED IN PART, AND REMANDED.