IIAR 2-2021: Emergency Pressure Control Systems
In the 2008 edition of Standard 2, IIAR first addressed the topic of emergency pressure control systems (EPCS). Prior to the publication of ANSI/IIAR 2-2021 earlier this year, each subsequent publication of Standard 2 has offered commentary on the subject of EPCS in an informative appendix.
ANSI/IIAR 2-2021 §15.6 is the first instance of EPCS in a mandatory paragraph of an IIAR standard. It reads as follows:
Where required by the AHJ, refrigeration systems that are required by Section 4.2 to be in a machinery room and which have pressure relief valves that release directly to atmosphere shall comply with this section. The system shall be evaluated to determine whether a release of ammonia from pressure relief valves would result in an unacceptable public health consequence. If an unacceptable public health consequence is determined, the installation shall comply with one of the following:
- An emergency pressure control system (EPCS) shall be installed. Use of an EPCS Shall not eliminate overpressure protection requirements of Section 15.3.
- Pressure relief valves shall use a relief method, other than direct atmospheric venting, permitted by Section 15.5.1.
While §15.6 is normative, the language of this paragraph indicates that it is only mandated if “required by the AHJ” (Authority Having Jurisdiction). Common AHJs that oversee the design of ammonia refrigeration systems are building and fire code officials who review construction plans as required to obtain a building permit. Put another way, during the review of the construction plan set, a building code official may require an evaluation of release scenarios from pressure relief valves. If unacceptable risk exists, the AHJ may require the system design to include an EPCS or prohibit the relief valves from terminating to atmosphere. §15.5.1 lists four methods for terminating relief valves when atmospheric termination is not permitted by an AHJ:
- Discharge through a treatment system,
- Discharge through a flaring system,
- Discharge through a water diffusion system,
- Discharge using other approved means.
ANSI/IIAR 2-2021 Appendix I contains helpful content regarding design, installation, operation, and pressure setpoints for an EPCS. This information is substantially the same as previous versions of IIAR 2 which we have written about in the past.