Ammonia Monitoring for Refrigeration Plants, Ice Rinks and Cold Storage

Is an ammonia detector required in a refrigeration machinery room?

Yes. This is one of the clearest detection mandates in the mechanical code, and the threshold that triggers a machinery room is low enough to capture almost every commercial ammonia system.

Section 1105.3 of the 2018 IMC states that refrigeration machinery rooms shall contain a refrigerant detection system with an audible and visual alarm, that the detector or a sampling tube drawing air to the detector shall be located in an area where refrigerant from a leak will concentrate, and that the alarm shall be actuated at a value not greater than the corresponding TLV-TWA value shown in the code for the refrigerant classification.

For ammonia, R-717, that value is 25 ppm.

Section 1104.2.1 sets the machinery room trigger for ammonia at systems where a release would exceed 25 percent of the lower flammability limit in the space, which in practice captures nearly everything.

What ventilation goes with the detector?

Normal ventilation continuously, and emergency ventilation on detector actuation, at rates the code takes from IIAR 2.

Section 1105.6.4 sets ammonia machinery room ventilation in accordance with IIAR 2: normal ventilation of not less than 2 cfm per square foot, and emergency ventilation of not less than 30 air changes per hour once the detection system actuates. Section 1106.3 requires ventilation to run continuously in ammonia machinery rooms, with a narrow exception tied back to 1105.6.4.

The detector is therefore not a standalone alarm. It is the input that switches the room from normal to emergency ventilation, which means the wiring and the interlock are part of the compliance story, not an optional extra.

How does ASHRAE 15 relate to the mechanical code here?

IMC Chapter 11 is the enforceable implementation, and ASHRAE 15 is the parent safety standard it implements. Chapter 11 states that ammonia refrigerating systems shall comply with the code and, except as modified by the code, with ASHRAE 15. IIAR 2 is separately referenced for the ammonia specific ventilation quantities.

In practice that means three documents sit behind one system, and where they differ, the adopted code governs. Design to the code your jurisdiction adopted, and use ASHRAE 15 and IIAR 2 for the engineering detail the code points at rather than as independent authorities.

What is the exposure limit for ammonia, and why is the alarm set lower?

Federally 50 ppm as an eight hour time weighted average. In California 25 ppm with a 35 ppm short term limit. The code alarm is set at 25 ppm because it follows the threshold limit value, not the OSHA limit.

29 CFR 1910.1000 Table Z-1 gives ammonia a permissible exposure limit of 50 ppm as an eight hour time weighted average. 8 CCR 5155 Table AC-1 sets the California limit at 25 ppm with a 35 ppm short term exposure limit.

Section 1105.3 ties the alarm to the TLV-TWA rather than to the OSHA number, which for ammonia is 25 ppm. So in California the code alarm and the exposure limit line up. Federally, the code alarm is deliberately set below the permissible exposure limit, which is the sensible way round.

Where should an ammonia sensor be placed?

Where a leak will concentrate, which for ammonia is not simply high or low.

Section 1105.3 requires placement in an area where refrigerant from a leak will concentrate, and deliberately does not give a height. Ammonia gas is lighter than air, but a release from a refrigeration system is cold and often carries liquid aerosol, so it initially behaves as a dense cloud and then rises as it warms and disperses.

The practical answer is to place sensors near the credible leak points, which are compressor shaft seals, valve groups, oil pots and piping joints, and to let the engineer of record work the placement against the room geometry and the ventilation path rather than applying a rule of thumb.

Ice rinks add a wrinkle worth naming: the machinery room is the regulated space, but the occupied space is the rink floor on the other side of the wall, and it is full of people who cannot smell an early leak over the cold.

Primary sources

M Squared Safety Solutions, Inc., 981 Calle Negocio Suite 200, San Clemente, CA 92673, 949-954-6581. Every code and regulatory statement on this page was read against the cited source on 18 September 2026. Model code section numbers are cited to the 2018 International Fire Code and International Mechanical Code. Jurisdictions adopt and amend these codes separately, so confirm the edition in force where the work is. This page describes what the regulations say. Whether a given provision is satisfied at a particular facility is a determination for that employer and the code official.