Standard Interpretations - Table of Contents|
| Standard Number:||1926|
October 28, 1993
Ms. Janet Fox
Dear Ms. Fox:
Your letter of July 16 to Mr. Roger Clark requesting information and clarification of the Occupational Safety and Health Administration (OSHA) soil classification requirements for excavations has been referred to the Office of Construction and Maritime Compliance Assistance for response. I apologize for the delay in responding to your inquiry.
The type A, B, and C soil classification system outlined in 29 CFR, Subpart P was developed to be a simple, easy to use method for estimating soil type in the field. The soil classification system takes into consideration that although the measurements provided by a thumb penetration test, a penetrometer, or a sheer vane are only estimates, these manual tests are meaningful and acceptable within the framework of the OSHA standards. With regard to your question why OSHA compliance officers use the penetrometer and sheer vane for soil analysis, please be advised that compliance officers normally prefer the penetrometer and/or sheer vane over the thumb penetration test because those instruments provide a reading that can be recorded.
With regard to your question whether the thumb penetration test is the only manual test necessary or must one or more additional manual tests be performed to classify a soil type A, B, or C, please be advised that Appendix A to Subpart P requires that the classification of soils be based on the results of at least one visual and at least one manual analysis. The choice of which visual and manual test is used is left up to the person responsible for making the test. If a thumb penetration test is performed in accordance with Appendix A, then no other manual test would be required. Please note that these tests are not necessary if type C soil is assumed and protection is provided for type C soil conditions.
If we can be of any further assistance, please contact me or Mr. Dale Cavanaugh of my staff at (202) 219-8136.
Mr. Roger Clark
Dear Mr. Clark,
I am writing to request information and clarification of the soil classification requirements for excavations set forth in Appendix A to Subpart P at 29 CFR 1926, Excavations. My questions arise from a conversation that one of Consolidated Edison's Safety Professionals had with an OSHA Compliance Officer.
During the conversation, the Senior Safety and Health Compliance Officer expressed some dissatisfaction with timeliness and with the actual results received from soil samples he sent to OSHA's laboratory in Salt Lake City, Utah. When we asked what the lab did differently from his analysis in the field, the Compliance Officer stated that he made his analysis using a penetrometer and a sheer vane.
Based on this conversation and two recent Review Commission Cases, Earl A. Eichline Enterprises, Inc. (16 OSHC 1223) and Southwestern Bell Telephone Company (16 OSHC 1021), I have come to the conclusion that the use of the penetrometer and the sheer vane is the standard test method used by Compliance Officers for soil analysis. What is troubling about this conclusion is the limitations of these devices, which the CO did not seem to recognize.
* "Saturation, or near saturation is necessary for the proper use of instruments such as a pocket penetrometer or sheer vane." (Appendix A, (b), Definitions, Saturated Soil).
* "OSHA notes that even the use of objective test procedures, such as the pocket penetrometer..., or the torvane sheer device, are still only estimates which are subject to error." (54 FR 45939)
* "Spangler and Hardy, in their book, Soil Engineering, ...., estimate the pocket penetrometer has a +/- 20 to +/- 40 percent error", and the authors also discuss some limitations of the torvane sheer device. (54 FR 45939)
It is because of these limitations that we have not considered using these devices for soil analysis. Also when used properly, these devices provide only an estimate of the unconfined compressive strength of the soil, which is the same result as the "thumb penetration" test will provide.
Which brings to me to my questions:
1. Why are OSHA Compliance Officers using the penetrometer and sheer vane for soil analysis?
2. Since the "thumb penetration" test provides the same information as these devices, is the "thumb penetration" the only manual test necessary or must one or more additional manual tests be performed to classify a soil A, B or C?
Thank you for your timely response to these questions.
Very truly yours,
Standard Interpretations - Table of Contents|