UNITED STATES OF AMERICA
OCCUPATIONAL SAFETY AND HEALTH REVIEW COMMISSION
SECRETARY OF LABOR,
OSHRC DOCKET NO. 76-910
ELECTRICAL CONSTRUCTORS OF AMERICA, INC.,
September 30, 1980
Before CLEARY, Chairman; BARNAKO and COTTINE, Commissioners.
BY THE COMMISSION:
A decision of Administrative Law Judge James D. Burroughs is before the Commission for review pursuant to section 12(j) of the Occupational Safety and Health Act of 1970, 29 U.S.C. §§ 651–678 (‘the Act’). Judge Burroughs affirmed a serious citation alleging that Respondent, Electrical Constructors of America, Inc., (‘Elcon’ or ‘the company’) violated section 5(a)(2) of the Act in that Elcon failed to shore or slope the sides of a trench as required by 29 C.F.R. § 1926.652(c). The judge assessed a penalty of $250. We reduce the penalty to $150, but otherwise affirm the judge’s decision.
At Hartsfield International Airport in Atlanta, Georgia, Elcon was engaged in relocating communications cable. This involved making a bore 125 to 140 feet long under an existing runway. To provide a place for the boring machine adjacent to and below the runway, Elcon excavated a trench approximately 48 feet long; six feet, four inches wide; and six to eight feet deep. The trench was in hard and compact soil. The excavation was performed using a John Deere 400 backhoe, an intermediate size backhoe having a downward reach of approximately thirteen feet, six inches. Elcon operated the backhoe at the trench edge.
The bore under the runway was required to be exact within a narrow range for error. Therefore, the trench depth and the level nature of the grade within the trench had to be as exact as possible. When the backhoe operator and the other Elcon employees at the worksite though the requisite depth and grade had been achieved, the employees and an engineer employed by the Federal Aviation Administration attempted to make accurate measurements of depth and grade from the ground surface, but found they could not do so. They entered the trench and were in the process of making the measurements when two compliance officers employed by the Secretary of Labor (‘the Secretary’) inspected the trenching worksite. The depth of the trench where the employees were working was at least six feet, and the trench sides were not shored or sloped above the five-foot level. Accordingly, a citation alleging that Elcon failed to comply with section 1926.652(c) was issued by the Secretary. The violation was characterized by the Secretary as serious. The characterization, according to the testimony of one of the compliance officers, was based on his own and other compliance officers’ experience which indicates that when a portion of a bank of dirt caves in on an employee, ‘he is usually seriously hurt.’ The Secretary proposed a penalty of $500.
Elcon did not contend before the judge that the trench complied with section 1926.652(c) but argued, instead, that shoring and sloping could not have been done until after the company had determined that the correct depth and grade had been reached. The company argued that if the sides were sloped back before the trench was completed, the backhoe could not reach the trench bottom to do any additional digging. The company further asserted that the degree to which the trench had to be sloped remained an unknown until the correct depth had been reached. Elcon also contended that the violation, if any, was not established as serious on the basis of the compliance officer’s unsupported opinion. The company additionally argued before the judge that no penalty was warranted in view of the low gravity of the violation, Elcon’s small size and precarious financial condition, and Elcon’s good faith as evidenced by compliance with the sloping requirements immediately after the inspection.
Judge Burroughs found that Elcon failed to comply with section 1926.652(c) and that the company’s defense of impossibility of performance was not established. He rejected Elcon’s contention that the backhoe could not reach the trench bottom if the sides were sloped. The judge noted that the six-to eight-foot sides in hard or compact soil were required to be sloped only at a rate of one-foot rise to each one-half-foot horizontal and only above the five-foot level. In light of the relatively small degree of sloping required and the fact that the reach of the backhoe was thirteen feet, six inches, which was considerably greater than the depth of the trench, Judge Burroughs concluded that the backhoe could have reached the bottom of the trench even if the walls had been properly sloped. The judge also found that the measurements of depth and grade could have been made with shoring in the trench. He accordingly rejected Elcon’s contention that shoring could not have been installed until after the correct depth and grade had been reached.
The judge further concluded that the violation was serious. He found that if a trench side measuring six feet high collapsed on an employee while the employee was bending over, ‘the chances are great that he would be completely covered,’ and that ‘the weight of the soil could possibly cause serious physical harm to an individual trapped by a collapse.’ The judge, however, assessed a penalty of $250, rather than the $500 proposed by the Secretary, because he concluded that the gravity of the violation was low in view of the small likelihood of a collapse of the hard and compact soil composing the trench walls.
On review, Elcon renews its arguments that a defense of impossibility of performance was established, that the violation was not serious, and that no penalty should be assessed. Elcon further argues that the judge’s factual findings on seriousness are not supported by the record and that the judge applied an incorrect legal test to determine that the violation was serious. Elcon notes that the judge considered whether a collapse of the trench sides ‘could possibly cause serious physical harm’ rather than whether there was ‘a substantial probability that death or serious physical harm could result,’ as set forth in section 17(k) of the Act. The Secretary did not file a brief on review.
We reject Elcon’s defense of impossibility of performance on the basis of the judge’s reasoning. We have examined the record and conclude that the judge properly considered the evidence and correctly rejected Elcon’s argument that the backhoe could not be used to excavate the trench further if the walls had been sloped to the extent required by the standard prior to the time the employees entered the trench. Accordingly, we adopt the judge’s findings and conclusions with respect to this issue. Gulf Oil Co., 77 OSAHRC 216/B10, 6 BNA OSHC 1240, 1978 CCH OSHD ¶ 22,737 (No. 14281, 1977). The remaining portion of Elcon’s defense—that the company could not know what slope was required until it had determined that the correct depth had been achieved—is plainly without merit, particularly since the record shows that the backhoe could have been used to correct the depth even after the sides had been sloped to the extent required for the depth existing at the time the employees were observed in the trench. Accordingly, Elcon has not established that compliance with the requirements of section 1926.652(c) for sloping was impossible because it would have precluded performance of the required work. See M. J. Lee Construction Co., 79 OSAHRC 12/A2, 7 BNA OSHC 1140, 1979 CCH OSHD ¶23, 330 (No. 15094, 1979).
We also reject Elcon’s arguments that the violation was improperly characterized as serious. A violation is deemed serious within the meaning of section 17(k) of the Act if there is a substantial probability that death of serious physical harm could result from an accident. The probability that an accident will occur is irrelevant. Boonville Division of Ethan Allen, Inc., 78 OSAHRC 105/B4, 6 BNA OSHC 2169, 1979 CCH OSHD ¶ 23,219 (No. 76–2419, 1978). We find that a collapse of the trench would have resulted in a substantial probability that the employees in the trench could have suffered death or serious physical harm. See Andy Anderson d/b/a Andy Anderson Irrigation and Construction, 78 OSAHRC 34/A2, 6 BNA OSHC 1595 (No. 76–4082, 1978). Therefore, the violation of section 1926.652(c) was serious.
There remains the penalty to be assessed. Because the gravity of the violation was low, Elcon has no prior history of violation of the Act, nothing appears to call into question Elcon’s good faith toward compliance, and the company is small in size, we assess a penalty of $150.
Accordingly, the judge’s decision is modified to assess a penalty of $150 and, as so modified, is affirmed. SO ORDERED.
FOR THE COMMISSION:
RAY H. DARLING, JR.
DATED: SEP 30, 1980
CLEARY, Chairman, concurring:
I would affirm the administrative law judge’s decision for the reasons assigned by him.
UNITED STATES OF AMERICA
OCCUPATIONAL SAFETY AND HEALTH REVIEW COMMISSION
SECRETARY OF LABOR,
OSHRC DOCKET NO. 76-910
ELECTRICAL CONSTRUCTORS OF AMERICA, INC.,
December 28, 1976
DECISION AND ORDER
Thomas P. Brown, IV, Esquire, Office of the Department of Labor, Atlanta, Georgia, on behalf of complainant.
John D. Sours, Esquire, Smith, Currie and Hancock, Attorneys at Law, Atlanta, Georgia, on behalf of respondent.
STATEMENT OF CASE
This is proceeding initiated pursuant to section 10(c) of the Occupational Safety and Health Act of 1970, 29 U.S.C. 651 et seq. (‘Act’). Respondent, by letter dated February 16, 1976, timely contested a serious citation issued to it, pursuant to section 9(a) of the Act, on February 4, 1976. Review is also sought of the penalty proposed for the alleged violation.
Respondent is a corporation having a place of business and doing business in Skyland, North Carolina. It is engaged in business as an electrical contractor. The citation resulted from an inspection conducted on January 30, 1976, at the Hartsfield International Airport, Atlanta, Georgia. Respondent was engaged in relocating a communications cable under a runway at the time of the inspection.
The serious citation alleges that respondent violated section 5(a)(2) of the Act by failing to comply with the safety standard promulgated at 29 C.F.R. § 1926.652(c). The alleged violation was described as follows:
Failed to shore or otherwise support the sides of trenches in hard or compact soil, more than five feet in depth and eight feet or more in length in which employees were exposed to the hazards of cave-ins in an open trench on the southside of runway #27R near fire station at Hartsfield International Airport.
A penalty of $500 was proposed for the alleged violation.
A hearing was held in this matter on July 6, 1976, in Decatur, Georgia. No additional parties desired to intervene in the proceedings.
JURISDICTION AND ISSUES
Respondent’s answer denied that the Commission has jurisdiction of this matter or that it is engaged in a business affecting commerce within the meaning of the Act. The denial was based on the contention that the allegations were legal conclusions.
Respondent admits in the Request for Admissions served upon it by complainant that it uses machinery, equipment and tools in its business that were manufactured in whole or part outside the State of Georgia (RA paras. 4, 5). Respondent’s president testified that respondent’s home office is in North Carolina and that it does business in North Carolina, Georgia and Tennessee (Tr. 54). These facts are sufficient to conclude that respondent is engaged in a business affecting commerce and that the Commission has jurisdiction of the parties and the subject matter. See Secretary v. Accu-Namics, Inc., 8 OSAHRC 890 (1974), aff’d 515 F.2d 828 (5th Cir. 1975), cert. den. 96 S.Ct. 1492 (1976).
The following issues are presented for determination:
1. Did respondent violate section 5(a)(2) of the Act by failing to comply with 29 C.F.R. § 1926.652(c)?
2. Was the violation, if it occurred, a serious violation within the meaning of section 17(k) of the Act?
3. What penalty, if any, should be assessed in the event a violation is determined?
FINDINGS OF FACT
The following facts are specifically determined in resolving the issues in dispute:
1. Respondent is a corporation with its home office located in Skyland, North Carolina. It currently operates in Georgia, Tennessee and North Carolina (Tr. 54).
2. Complainant, through a duly authorized compliance officer, conducted an inspection at the Hartsfield International Airport, Atlanta, Georgia, on January 30, 1976 (Tr. 5, 12).
3. At the time of the inspection, respondent was in the process of completing the excavation of a trench. Approximately 90 percent of the trench had been completed the previous day (Tr. 5, 58).
4. Respondent had 17 employees at the airport at the time of inspection (Tr. 24). Some of the employees were working at another excavation site at the airport (Tr. 24–25).
5. Respondent had a contract with the Federal Aviation Administration at Hartsfield Airport to relocate all communications cables from existing facilities to a new tower location (Tr. 56).
6. A trench had been excavated at the southside runway of the airport. The trench was approximately 48 feet long and six feet and four inches wide. The depth of the trench varied between six and eight feet. It was seven feet deep in the center, eight feet deep at the runway and six feet deep at the opposite end (RA paras. 6–9, Tr. 6, 35).
7. The trench was excavated in hard and compact soil. The sides of the trench were not shored, sheeted, braced or otherwise supported (RA paras. 10, 12; Exs. 1, 2; Tr. 11).
8. The trench was not sloped (Exs. 1, 2). Respondent had intended to slope the trench after the proper grade and depth had been reached (Tr. 63).
9. Three employees of respondent were in the trench at the time of the inspection (Ex. 1; Tr. 7, 9, 40). They were in the area of the trench that was six feet deep (Exs. 1, 2; Tr. 46–47).
10. The grade of the trench had to be checked. Three employees entered the trench to perform this task. The equipment operator was in the trench assisting in checking the grade and depth at the time of the inspection (Ex. 1; Tr. 39–40, 42). Two laborers were also in the trench. One laborer spread the dirt so a good measurement could be taken (Tr. 50, 52–53). An engineer for the Federal Aviation Administration was in the trench checking the grade and depth (Tr. 42–43, 73–74, 76).
11. The employees had been in the trench approximately one to two minutes when the compliance officer arrived (Tr. 43–44, 74).
12. The trench was excavated in order to place a boring machine in it to bore under the runway. Communications cables had to be place under the runway (Tr. 18–19, 37, 41).
13. The boring machine was to be placed in the trench after the proper grade had been established (Tr. 56).
14. The boring machine was to be placed on a track similar to a railroad track. The track had to be level and at the right pitch (Tr. 56–57, 59).
15. The length of the bore under the runway was to be between 125 and 140 feet. The bore had to be made in an exact and precise direction (Tr. 57).
16. The depth of the trench had to be checked at the place where the boring machine was to be placed. In order to get an accurate measurement, the engineer for FAA and respondent’s employees thought it necessary to go into the trench (Tr. 75).
17. Respondent does not generally slope excavations in which boring machines are to be placed until the excavation has been completed. This procedure is followed because the slope further limits the reach of the backhoe into the excavation (Tr. 60–61, 63).
18. Respondent was using a John Deere 400 backhoe to excavate the trench. It had a reach of 13 feet and six inches (Tr. 62).
19. Shoring of the trench would not have interfered with obtaining an accurate measurement of the grade and level of the trench (Tr. 78).
As a result of an inspection conducted on January 30, 1976, at respondent’s job site at Hartsfield International Airport, Atlanta, Georgia, respondent was issued a serious citation on February 4, 1976. Complainant alleges that respondent violated 29 C.F.R. § 1926.652(c) by failing to shore or otherwise support the sides of a trench excavated in hard or compact soil.
The undisputed evidence establishes that three employees of respondent were in a trench that was 48 feet long and six feet and four inches wide. The depth of the trench varied between six and eight feet. The soil was hard and compact. The trench was not sloped, shored, sheeted, braced or otherwise supported. It is clear that the requirements of 29 C.F.R. § 1926.652(c) were violated.
Respondent contends that the inspection was improper and unwarranted. It is pointed out that the job site was at a remote area of the airport and was not frequented by the public or open to ready public view. Under the rationale expressed in Brennan v. Gibson’s Products, Inc., 407 F.Supp. 154 (E.D. Tex. 1976), and Secretary of Labor v. Rupp Forge Company, —— F.Supp. —— (N.D. Iowa 1976), it is argued that complainant could not properly conduct the inspection without first obtaining a search warrant.
In Gibson Products, Inc., the compliance officer attempted to inspect the nonpublic portion of a store operated by respondent. It refused to permit the inspection. The court concluded that the Fourth Amendment of the United States Constitution mandated that a search warrant be obtained for resisted inspections. The decision in Rupp Forge Co. followed the rationale as expressed in Gibson Products, Inc.
Respondent’s reliance on the rationale of the court in Gibson Products, Inc. is misplaced. There has been no showing that the inspection conducted by the compliance officer was resisted by respondent. On the contrary, the evidence clearly shows that employees of respondent consented to the inspection. In addition, the inspection was not conducted on respondent’s premises. In Accu-Namics, Inc. v. OSAHRC and Secretary of Labor, 515 F.2d 828 (5th Cir. 1975), cert. den. 96 S.Ct. 1492 (1976), the court concluded that there was no fourth amendment right where the inspection was not conducted on the employer’s premises. In that case, the job site was a public street. In the present case the inspection was conducted on the premises of the airport which is owned and operated by the City of Atlanta.
Respondent also argues that literal compliance with § 1926.652(c) would have made it impossible to perform the required task of checking the grade and depth of the trench. There is no dispute that the grade and level of the trench had to be checked prior to the boring machine being placed in the trench. The engineer for the FAA testified that he attempted to perform the measurement at ground level but that the measurement had to be made in the middle of the trench where the boring machine would be placed (Tr. 75). In order to obtain an accurate measurement, he thought it necessary to enter the trench.
It is contended that the trench could not be sloped until the correct grade and level had been achieved. This argument is based on the limited reach of the backhoe. A slope means the backhoe must operate further from the center of the trench (Tr. 60–61). The backhoe being used had a reach of 136’ (Tr. 62). The trench depth varied from six to eight feet. Since the soil was hard and compact, the slope would not have had to commence until the five foot level. The evidence does not establish that the backhoe could not reach the center of the trench if a proper slope had been made prior to the employees entering the trench. This is especially true since respondent usually operates its equipment right at the edge of the slope (Tr. 62).
The FAA engineer testified that the shoring of the trench would not have interfered with the accuracy of the measurement (Tr. 78). Shoring would have caused some inconvenience but it certainly would not have made it impossible to perform the grade and level measurements. The defense of impossibility of performance is without merit. The violation has been established.
NATURE OF VIOLATION
Complainant alleges that the violation of 29 C.F.R. § 1926.652(c) was a serious violation within the meaning of section 17(k) of the Act. The Commission has held that the occurrence of an accident because of an existing hazard in violation of the Act need not be substantially probable in order for a violation to be serious. An accident must simply be possible. Serious and non-serious violations ‘are distinguished on the basis of the seriousness of injuries which experience has shown reasonably likely to occur.’ Secretary v. Natkin and Company, 2 OSAHRC 1472 (1973). The probability of an accident occurring is relevant only to the gravity of the violation. See Secretary v. Emory H. Mixon, 5 OSAHRC 579 (1973).
Respondent was aware of the fact that employees usually entered the trench in making the grade and level measurements. Respondent either knew of the violation or could have known of it by the exercise of reasonable diligence. Respondent does not contend that the violation was unknown to it or that the presence of the employees in the trench was contrary to its instructions. The issue must be decided on the basis of the type of injuries employees were likely to have incurred in the event a collapse of the trench walls had occurred.
The trench varied in depth from six to eight feet. The evidence does not establish the exact depth at the portions of the trench where employees performed the grade and level measurements. The likelihood of employees being fully covered at the six foot level in an upright position is considered remote. However, a collapse at the six foot level would certainly cover a great portion of the body of anyone caught in an upright position. If the employee were in a bending position, the chances are great that he would be completely covered. In either event, the weight of the soil could possibly cause serious physical harm to an individual trapped by a collapse. The violation is deemed to be serious within the meaning of section 17(k) of the Act.
The Commission is the final arbiter of penalties in all contested cases. Secretary v. Occupational Safety and Health Review Commission and Interstate Glass Co., 487 F.2d 438 (8th Cir. 1973). Under section 17(j) of the Act the Commission is required to find and give ‘due consideration’ to the size of the employer’s business, the gravity of the violation, the good faith of the employer and the history of previous violations in determining the assessment of an appropriate penalty. The gravity of the offense is the principal factor to be considered. Secretary v. Nacirema Operating Company, Inc., 1 OSAHRC 33 (1972).
Three employees of respondent were in the trench. They were present in the trench for only a brief period of time. The soil was hard and compact. The depth was only six to eight feet. The possibilities of a collapse in hard and compact soil at that level is considered remote. This is especially true since there is no evidence, such as water in the trench or other indicia of a weakening in the walls, to indicate there was any cause for real concern by the respondent for the safety of its employees. A penalty of $250 is assessed.
CONCLUSIONS OF LAW
1. Respondent, at all times material hereto, was engaged in a business affecting commerce within the meaning of section 3 (5) of the Act.
2. Respondent was subject to the requirements of the Act and the standards promulgated thereunder. The Commission has jurisdiction of the parties and of the subject matter herein.
3. On January 30, 1976, three employees of respondent were in a trench which varied in depth from six to eight feet. The soil was hard and compact.
4. The trench was not sloped, shored, braced or otherwise supported in violation of 29 C.F.R. § 1926.652(c).
5. The violation was serious. A penalty of $250 is assessed for the serious violation.
Upon the basis of the foregoing findings of fact and conclusions of law, it is
(1) That the serious citation issued to respondent on February 4, 1976, is affirmed; and
(2) That the notification of proposed penalty issued to respondent on February 4, 1976, is modified to assess a penalty of $250 for the serious violation.
Dated this 28th day of December, 1976.
JAMES D. BURROUGHS
 29 U.S.C. § 661(i).
 29 U.S.C. § 654(a)(2).
 29 C.F.R. § 1926.652(c) provides the following:
§ 1926.652 Specific trenching requirements.
(c) Sides of trenches in hard or compact soil, including embankments, shall be shored or otherwise supported when the trench is more than 5 feet in depth and 8 feet or more in length. In lieu of shoring, the sides of the trench above the 5-foot level may be sloped to preclude collapse, but shall not be steeper than a 1-foot rise to each ½-foot horizontal. When the outside diameter of a pipe is greater than 6 feet, a bench of 4-foot minimum shall be provided at the toe of the sloped portion.
 A serious violation is defined in § 17(k) of the Act, 29 U.S.C. § 666(j), which states the following:
For purposes of this section, 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, or from one or more practices, means, methods, operations, or processes which have been adopted or are in use, 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.
 Chairman Cleary granted Elcon’s petition for review, which raised these issues. Additionally, former Commission Member Moran directed review of the judge’s decision ‘for error.’ In a letter submitted in lieu of a brief on review, Elcon referred the Commission to its post-hearing brief, in which the company additionally had argued that the inspection was improperly conducted. It is clear, however, that Elcon does not seek modification or reversal of the judge’s decision rejecting this contention. In its letter filed subsequent to the directions for review, Elcon asserted that the company’s petition and post-hearing brief provided adequate support for ‘Respondent’s position in this matter, and fully demonstrate that Respondent has made good the defense of impossibility, that any violation, if found, is to be classed as non-serious, and that, in any event, no penalty should be assessed against Respondent. . . .’ Elcon did not direct attention to the inspection issue. Accordingly, the issue of whether the inspection was proper is not before the Commission for review. See Water Works Installation Corp., 76 OSAHRC 61/B8, 4 BNA OSHC 1339, 1976–77 CCH OSHD ¶ 20,780 (No. 4136, 1976); Abbott-Sommer, Inc., 76 OSAHRC 21/A2, 3 BNA OSHC 2032, 1975–76 CCH OSHD ¶ 20, 428 (No. 9507, 1976). Such unreviewed dispositions of a Commission judge are not precedent binding on the Commission. See Leone Constr. Co., 76 OSAHRC 12/E6, 3 BNA OSHC 1979, 1975–76 CCH OSHD ¶ 20,387 (No. 4090, 1979).
 Note 4 supra.
 The two compliance officers testified that they could and did measure the depth of the trench from the ground surface and described in some detail how this measurement should be made to assure substantial accuracy.
Elcon did not argue that sloping the sides of the trench before the employees went into it would prevent them from making a sufficiently precise measurement of the depth for the purpose of successfully completing the bore. Moreover, the Federal Aviation Administration engineer, who testified on behalf of Elcon, admitted that the necessary measurement could be made with the trench sides sloped, although he stated that making the measurement would be more difficult.
 In addition to requiring an initial showing of impossibility, either of compliance or performance, we also have required that the employer show that alternative means of protection were in use or were unavailable in order to sustain the defense of impossibility. See Bill C. Carroll Co., 79 OSAHRC 87/C13, 7 BNA OSHC 1806, 1979 CCH OSHD ¶23,940 (No. 76–2748, 1979); M. J. Lee Constr. Co., supra. However, we need not consider this aspect of the defense because, as we have indicated, Elcon failed to show that compliance would have precluded performance of the required work.
As has been indicated, Elcon also argued and continues to argue that the use of shoring would have precluded performance of the required work. Because the record shows that Elcon could have complied with § 1926.652(c) by sloping the sides of the trench, we need not consider whether Elcon has established an impossibility defense as to shoring.
 That the employer either knew or could have known, with the exercise of reasonable diligence, of the presence of the violation is the remaining element of a serious violation. However, Commissioner Cottine does not reach the question of employer knowledge in this case because Elcon has not argued, either before the judge or before the Commission, that the violation was not established as serious because it lacked the requisite knowledge of the violation. See Brown-McKee, Inc., 80 OSAHRC ___, 8 BNA OSHC 1247, 1251 n. 8, 1980 CCH OSHD ¶ 24,409 at 29,738 n. 8 (No. 76–982, 1980).
Commissioner Barnako, on the other hand, believes that the element of knowledge must be addressed here because it is an element of the Secretary’s proof of a violation. Brown-McKee, Inc., supra; Scheel Constr., Inc., 76 OSAHRC 138/B6, 4 BNA OSHC 1825, 1976–77 CCH OSHD ¶ 21,263 (No. 8687, 1976). He would find that knowledge has been established in view of the evidence that Elcon’s crew superintendent was at the unprotected trench when the company’s employees went into it to make the depth and grade measurements.
 RA refers to complainant’s Request for Admissions served upon respondent on June 14, 1976, and respondent’s answers which were served upon complainant on June 29, 1976.
 Exhibit one shows four persons in the trench. The compliance officer testified that one of them was not an employee of respondent (Tr. 9).
 29 C.F.R. § 1926.652(c) provides:
(c) Sides of trenches in hard or compact soil, including embankments, shall be shored or otherwise supported when the trench is more than 5 feet in depth and 8 feet or more in length. In lieu of shoring, the sides of the trench above the 5-foot level may be sloped to preclude collapse, but shall not be steeper than a 1-foot rise to each 1/2-foot horizontal. When the outside diameter of a pipe is greater than 6 feet, a bench of 4-foot minimum shall be provided at the toe of the sloped portion.
 Section 1926.652(c) requires that the slope ‘shall not be steeper than a 1-foot rise to each 1/2-foot horizontal.’
 Section 17(k) of the Act provides:
(k) For purposes of this section, 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, or from one or more practices, means, methods, operations, or processes which have been adopted or are in use, 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.