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 2, 2017

Mr. Lee Paulsen
Midwest Farmers Cooperative
304 S. 3rd Street
PO Box 40
Elmwood, Nebraska 68349

Dear Mr. Paulsen:

Thank you for your letter to the Occupational Safety and Health Administration (OSHA).  Your letter was referred to OSHA’s Directorate of Enforcement Programs for reply.  This letter constitutes OSHA’s interpretation only of the requirements referenced below and may not be applicable to any question not included in your original correspondence.  You requested clarification on what constitutes an incidental release versus a release requiring an emergency response under 29 CFR 1910.120(q), Emergency Response to Hazardous Substance Releases.  We apologize for the delay in our response.

Your question is paraphrased below, and our response follows.

Scenario:  Among other agricultural services, Midwest Farmers Cooperative (MFC) maintains a system where anhydrous ammonia is stored, dispensed into smaller containers, and subsequently sold to the agricultural community as fertilizer.  In general, any potential release of anhydrous ammonia from this system would be in an outdoor setting, not confined to a room or building.  You indicated that MFC stores anhydrous ammonia outdoors and that your equipment can be affected by the weather.  Materials such as seals and gaskets can expand or contract based on the air temperature.  When this occurs, there may be small product releases that you stated are limited in quantity and pose no potential safety or health hazards.  You explained that employees can deal with these releases by tightening or turning off valves.

It is your goal to treat these as incidental releases that can be addressed by employees on site without triggering an emergency response subject to the requirements of OSHA’s Hazardous Waste Operations and Emergency Response (HAZWOPER) standard (29 CFR 1910.120(q)).  You noted that in any situation that would compromise employee safety, MFC would evacuate employees in accordance with an Emergency Action Plan (EAP), as permitted by 29 CFR 1910.120(q)(1).  In most anticipated scenarios involving the releases you characterize as incidental, employees would not be located in the immediate release area. Employees would need to access the site from outside the area to correct the release.

Question:  Can MFC treat some small releases of anhydrous ammonia as incidental releases, or must all releases of anhydrous ammonia be treated as emergency response situations under the HAZWOPER standard?

OSHA Response:  Paragraph (q) of the HAZWOPER standard applies to emergency response operations for releases of, or substantial threats of releases of, hazardous substances.  See 29 CFR 1910.120(a)(1)(v), (a)(2)(iv).  OSHA has defined an emergency response as “a response effort by employees from outside the immediate release area or by other designated responders (i.e., mutual-aid groups, local fire departments, etc.) to an occurrence which results, or is likely to result, in an uncontrolled release of a hazardous substance.”  See 29 CFR 1910.120(a)(3).  Incidental releases of hazardous substances that can be absorbed, neutralized, or otherwise controlled at the time of release by employees in the immediate release area or by maintenance personnel, and responses that do not involve exposure to potential safety or health hazards, are not considered to be emergency response scenarios.  See 29 CFR 1910.120(a)(3).  As discussed in more detail later in this response, it is possible that some releases of anhydrous ammonia may constitute incidental releases, but whether a particular situation involves an incidental release or necessitates an emergency response must be determined by the employer on a case-by-case basis.

As you are aware, OSHA has written extensively on this subject and has not established specific airborne concentrations, spill volumes, release rates, etc. at which an event transitions from an incidental release to a release requiring emergency response.  Following is a non-exhaustive list of OSHA publications and letters on this issue:

  1. Inspection Procedures for 29 CFR 1910.120 and 1926.65, Paragraph (q):  Emergency Response to Hazardous Substance Releases, CPL 02-02-073, August 27, 2007 [www.osha.gov/enforcement/directives/cpl-02-02-073];
  2. OSHA Letter of Interpretation, “Definition of an Emergency Response,” Andree, June 29, 1992 [www.osha.gov/laws-regs/standardinterpretations/1992-06-29];
  3. OSHA Letter of Interpretation, “OSHA’s Hazardous Waste Operations and Emergency Response,” Brooks, August 27, 1991 [www.osha.gov/laws-regs/standardinterpretations/1991-08-27];
  4. OSHA Letter of Interpretation, “Application of the Hazardous Waste Operations and Emergency Response Standard to Specific Operations,” Huston, July 25, 1990 [www.osha.gov/laws-regs/standardinterpretations/1990-07-25].

In CPL 02-02-073, Appendix A, OSHA states that an emergency response can include, but is not limited to, the following situations:

  1. The response comes from outside the immediate release area;
  2. The release requires evacuation of employees in the area;
  3. The release poses, or has the potential to pose, conditions that are immediately dangerous to life or health (IDLH);
  4. The release poses a serious threat of fire or explosion (exceeds or has the potential to exceed the lower explosive limit or lower flammable limit);
  5. The release requires immediate attention because of a potential imminent danger;
  6. The release may cause high levels of exposure to toxic substances;
  7. There is uncertainty about whether the employees in the work area can handle the severity of the hazard with the personal protective equipment and other equipment that has been provided and the exposure limit could easily be exceeded; and
  8. The situation is unclear, or data are lacking for important factors.

See CPL 02-02-073, pp. A-3 to A-4.  The directive also explains that incidental releases are those releases that neither pose a significant safety or health hazard to employees in the immediate vicinity or to the employees cleaning it up, nor have the potential to become an emergency within a short time frame.  Incidental releases are limited in quantity, exposure potential, or toxicity and present minor safety or health hazards to employees in the immediate work area or those assigned to clean them up.  (Note that while employees asked to address incidental releases are not covered by 29 CFR 1910.120(q), they must still have the proper equipment and training under other OSHA standards, such as the Hazard Communication Standard (29 CFR 1910.1200).)  See CPL 02-02-073, p. A-1.  You correctly noted in your letter that a release situation is not necessarily an emergency response scenario simply because the employee who addresses the release comes from another area of the worksite.  See CPL 02-02-073, p. A-5.

Before a release occurs, the employer should consider:

  • Possible release scenarios;
  • The means used to detect a release;
  • The means used to determine release rate, release location, and the potential for a release to become exacerbated;
  • The means that will be used to correct, mitigate, or stop the release;
  • Potential employee exposure while performing activities to correct, mitigate or stop the release; and
  • Other relevant information, e.g., the chemical hazards in question, the training and experience of the employees who would address the release, and the presence of engineering controls.

With respect to anhydrous ammonia specifically, it is important to remember that anhydrous ammonia is a highly hazardous, toxic chemical stored in pressurized ASME or DOT vessels or containers.  The OSHA permissible exposure limit (PEL) is 50 ppm (8-hour time weighted average) (see 29 CFR 1910.1000, Table Z-1) and the IDLH limit is 300 ppm1.  Even small releases can threaten the health and safety of employees.        

The response activities you describe include turning off valves and repairing or tightening leaking gaskets, seals, or fittings on the ammonia system or nurse tanks caused by environmental factors, such as temperature fluctuations.  These activities have the potential to result in catastrophic releases depending on the condition of the equipment, piping supports, conditions and stress of the valves and fasteners, and many other factors.  Therefore, OSHA believes it is possible, and indeed likely, that any given release of anhydrous ammonia in your scenario will necessitate an emergency response in accordance with the requirements of 29 CFR 1910.120(q).2  Extremely small vapor releases, such as minor valve packing leakage and similar releases where exposures in the breathing zone of the employee would be less than the PEL and there is no risk of a catastrophic release, may be considered incidental.  EAP procedures should specifically address the criteria used to determine whether a particular release is incidental. 

Thank you for your interest in occupational safety and health.  We hope you find this information helpful.  OSHA’s requirements are set by statute, standards, and regulations.  Our letters of interpretation do not create new or additional requirements but rather explain these requirements and how they apply to particular circumstances.  This letter constitutes OSHA’s interpretation of the requirements discussed.  From time to time, letters are affected when the Agency updates a standard, a legal decision impacts a standard, or changes in technology affect the interpretation.  To assure that you are using the correct information and guidance, please consult OSHA’s website at [www.osha.gov].  If you have further questions, please feel free to contact the Directorate of Enforcement Programs at (202) 693-2100.



Patrick J. Kapust, Acting Director

Directorate of Enforcement Programs


[Correction 1/28/2021]

1 https://www.cdc.gov/niosh/idlh/7664417.html [Back to Text]

2 As you note in your letter, an employer’s compliance obligations under 29 CFR 1910.120(q) are satisfied if the employer will evacuate its employees from the danger area when an emergency occurs, does not permit any of its employees to assist in handling the emergency, and provides an EAP in accordance with 29 CFR 1910.38.  See 29 CFR 1910.120(q)(1). [Back to Text]