OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

October 12, 1995

Ms. Janis A. Morelli
Elizabethtown Water Company
600 South Avenue
Westfield, NJ 07091-0788

Dear Ms. Morelli:

This is in response to your September 28 letter requesting interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals standard, 29 CFR 1910.119. Specifically, you requested clarification on whether the ozone process described in your letter is covered by the PSM standard.

As indicated in your letter, ozone is generated and flows directly into concrete contractors where it is used, that is, neutralized in its reaction with impurities in the water at a treatment plant. Since the amount of ozone, that is, 3 to 4 pounds (1.36 to 1.81 kg), in the process at any one time is less than the threshold quantity of 100 pounds (45.35 kg), the process would not be covered by the PSM Standard.

We appreciate your interest in occupational safety and health. If we can be of further assistance, please contact Mr. Ronald Davies of my staff, telephone (202) 219-8031, extension 110.


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

September 28, 1995

Mr. Ray Donnelly
Office of General Industry
Compliance Assistance OSHA
200 Constitution Avenue, N.W.
Washington, D.C. 20210

Re: Process Safety Management Standard 1910.119 Request for Interpretation

Dear Mr. Donnelly:

On September 22, 1995 I spoke with Mr. Ron Davies of your office who advised me to write to you regarding a request for a standard interpretation letter. I would like your determination regarding the applicability/non-applicability of OSHA's Process Safety Management Standard, 29 CFR 1910.119, to the following ozone process.

The Elizabethtown Water Company (EWC) is constructing a new potable water treatment plant in New Jersey. The plant will be constructed with an initial treatment capacity of 40 million gallons per day (MGD), and the potential for an ultimate treatment capacity of 200 MGD. The plant will utilize ozonation to oxidize metals, organic turbidity, taste and odor constituents, and as primary disinfection. At the initial water treatment capacity of 40 MGD, approximately 2,000 pounds per day of ozone will be required, or slightly more than 83 pounds per hour.

Ozone will be generated on-site for direct diffusion into the water. The ozonation process is a process which ozone gas is produced from an oxygen bearing carrier gas, for this facility, dehumidified ambient air. Air feed systems will be provided for the preparation of dry air feed to the ozone generators. Three ozone generating trains will be provided for the initial water treatment capacity of 40 MGD with additional space provided in the chemical building for three more trains. The ozone generators will be medium frequency (400-625 Hz) systems with a combined generating capacity of 4,000 pounds per day with one unit out of service.

Under operation conditions, the generators will be used at partial capacities to provide a combined daily generation of approximately 2,000 pounds per day. This configuration will provide required redundancy and operating reliability.

When the treatment plant capacity is expanded to 100 MGD, one additional generator train will be installed, enabling the production of 6,000 pounds per day of ozone with one standby unit. At ultimate plant capacity of 200 MGD, six trains will be installed to provide 10,000 pounds per day with one unit as a standby.

Ozone will flow directly form the generators into closed concrete contactors. Approximately 90 percent of the ozone, or 1,800 pounds per day will be neutralized in its reaction with impurities within the water. The remaining 200 pounds per day will be off gassed into the headspace air above the water in the contractors, and drawn into catalytic destruction units.

The PSM Standard is concerned only with the total maximum amount of ozone in a process. With the initial ozonation equipment, approximately 3 to 4 pounds of ozone will be present in the system at any one time. When the ozone generating capacity is increased sometime in the year 2015 to a projected generating capacity of 10,000 lbs/day, the maximum ozone present will be approximately 6 to 7 pounds still well below the 100 pound PSM threshold.

I am aware that OSHA's standard interpretation will only be valid for the process as described herein at its initial generating capacity and under the regulations presently in effect. I am not requesting a determination be made on future generating capacities as we are not aware of the regulations which may apply at a later date.

Please advise me whether this ozone generation process would be subject to the OSHA PSM Standard, 29 CFR 1910.119. Feel free to contact me at (908)654-1234 extension 270 if I can provide you with any additional information.

I look forward to your reply.


Janis A. Morelli
Manager Safety