Sulfur dioxide concentrations under process safety rules

April 29, 1997

Maureen J. Wall
Senior Project Engineer
Environmental Resources Management, Inc.
[Recipient address omitted]
Dear Ms. Wall:

This letter rescinds the Occupational Safety and Health Administration's (OSHA) letter of December 11, 1996, responding to your letter of September 27 concerning the Process Safety Management (PSM) Standard, and provides you with a new response to your questions, which includes your follow-up clarification request in your letter dated January 3, 1997. We apologize for any inconvenience this may have created.

You indicated that you understood that the highly hazardous chemicals listed in Appendix A which do not also list concentration criteria involving a threshold quantity of a commercial grade of the listed chemical are not covered by the PSM standard. The toxic and reactive chemicals list in Appendix A are "commercial grade" concentrations. OSHA has defined "commercial grade" as the typical maximum concentration of the chemical that is commercially available and shipped. The term "commercial grade" includes reagent grades, which in some cases, reflect concentrations different from those found in typical commercial grades.

In light of the concentration criteria, you then inquired about the coverage of gaseous sulfur dioxide versus the Appendix A description of sulfur dioxide, liquid. If you refer to page 6365 of the FEDERAL REGISTER notice, in the middle column near the end of the full paragraph, OSHA states its intention to eliminate the word "liquid" from the description of sulfur dioxide because sulfur dioxide could also be a gas and the health hazards were the same regardless of its state. This correction did not appear in the final rule's Appendix A but OSHA is planning to correct this entry in the near future. Since the sulfur dioxide you describe does not meet the concentration criteria, the presence of sulfur dioxide in your combustion gas would not be the basis for PSM coverage.

We hope this information is of assistance to you. If you need further assistance, please contact my staff members, Ron Davies at 202-219-8031 or Mike Marshall at 202-219-8118 ext. 12.

Sincerely,
John B. Miles, Jr., Director
Directorate of Compliance Programs