Refrigerant Leak Detection Systems – Do What?
Let’s start with the detectors themselves. It’s important to begin by pointing out that model codes and standards don’t limit the requirements for leak detection to refrigeration systems that use ammonia.
Once a machinery room is required, even for Safety Group A1 refrigerants, leak detection in the machinery room is mandatory. Leak detection is actually more important for Safety Group A1 refrigerants than for ammonia because ammonia’s self-alarming odor will force an evacuation response by occupants at concentrations well below those that trigger acute health or fire safety concerns. In contrast, a leak of an odorless Safety Group A1 refrigerant can reach dangerous concentrations without any indication of the impending danger to occupants or emergency responders. That danger can be compounded if the refrigerant comes into contact with an open flame device, which can lead to extremely dangerous and odorless combustion byproducts.
Although the science of refrigerant leak detection and the equipment used are well-developed, the codes and standards that regulate leak detection systems largely defer to the judgment of design professionals. The lack of regulatory constraint comes with pros and cons. On the plus side, codes and standards, as they are currently written, are flexible enough to accommodate variations in field erected systems. On the minus side, the lack of clear benchmarks for determining code compliance can lead to job delays and cost overruns when designers and enforcers interpret the code differently.
As an example, look at the requirements for placement of leak detection devices. ASHRAE 15, Section 8.11.2.1 states “Each refrigerating machinery room shall contain a detector, located in an area where refrigerant from a leak will concentrate.” Uniform Mechanical Code (UMC) Section 1107.4 contains similar text “Machinery rooms shall be provided with approved refrigerant-vapor detectors sensing where refrigerant from a leak is likely to concentrate.” If you read these two sections quickly, they might appear to be the same, but look closely. ASHRAE 15 requires “a detector” and the UMC requires “approved refrigerant vapor detectors.”
A subtle but important difference is that the UMC text includes the word “approved,” which provides clear authority to the code official to accept or reject the type of detection device that will be permitted. Might it be possible for the code official to require that detection devices be listed by a third-party testing laboratory? There is nothing to prohibit the code official from applying the code in that way, and given the broad definition of the word “approved” and the lack of guidance in the code as to what the code official should contemplate in determining approval, the answer is yes (albeit no such devices are currently available).
Look at the code text again, ASHRAE 15 uses the singular word “detector;” whereas, the UMC uses the plural “detectors.” Should this be taken to imply that more than one detector must be provided? In the case of ammonia, the answer is yes, but for a different reason. IIAR-2 Section 13-2 requires “Each refrigerating machinery room shall contain at least two refrigerant detectors.” This text leaves open the question of whether more than two detectors might be needed. Some may argue that a large room might need additional detectors, and because neither codes nor standards specify linear distance or area limits for detectors there is no conclusively right or wrong answer. For now, the determination is largely left to device manufacturers and system design engineers, but lacking third-party testing or listing of detectors, the current system relies on a code official trusting design recommendations. This can be a problem considering that code officials are more accustomed to dealing with smoke and carbon monoxide detectors, which require third-party listings and are highly regulated with respect to permissible spacing and location.
The potential for conflict over differing code interpretations related to leak detector location is clear. Additional requirements in the International Mechanical Code; NFPA 72 National Fire Alarm Code; model fire codes don’t make things better. Then, for ammonia refrigeration, there is one more very important consideration. The exceptions that allow storage and processing areas to contain ammonia refrigeration equipment provided in ASHRAE 15 and the model mechanical codes are all conditional, based on leak detection being provided. These exceptions include the following text:
ASHRAE 15, Section 7.2.2 (4) “Refrigerant detectors are installed with the sensing location and alarm level as required in refrigerating machinery rooms in accordance with Section 8.11.2.1.”
UMC Section 1105.3.1 “The refrigerated room or space is equipped with a refrigerant vapor detection and alarm system complying with Section 1121.0.”
IMC Section 1104.2.2 (4) “Refrigerant detectors are installed as required for machinery rooms in accordance with Section 1105.3.”
All of these sections point back to the detection requirements for machinery rooms discussed above. So, questions about the minimum required number and spacing of ammonia detectors extend beyond machinery rooms to include refrigerated storage and processing areas, which are often larger and may have complex floor plans.
A second example of code text that may lead to conflicting interpretations involves the alarm signal that leak detectors are required to initiate. As was the case for locating refrigerant detectors, codes and standards provide little guidance with respect to what type of alarm signal must be provided:
ASHRAE 15, Section 8.11.2.1 “Each refrigerating machinery room shall contain a detector…that actuates an alarm…at a value not greater than the corresponding TLV-TWA (or toxicity measure consistent therewith). The alarm shall annunciate visual and audible alarms inside the refrigerating machinery room and outside each entrance to the refrigerating machinery room…Alarms set at other levels (such as IDLH) and automatic reset alarms are permitted in addition to those required by this section…” (See also Informative Appendix F, which includes the statement “The refrigerant detector…triggers alarms inside and outside the refrigerating machinery room; signage warns refrigeration technicians and bystanders not to enter when the alarm has activated.” UMC, Section 1107.4 “Machinery rooms shall be provided with approved refrigerant-vapor detectors… that will activate visual and audible alarms inside the refrigerating machinery room, outside each entrance to the refrigerating machinery room and…Alarms shall be activated at a value not exceeding one-half the immediately dangerous to life or health (IDLH), or measurement consistent therewith; the PEL, or measurement consistent therewith; or 25 percent of the LFL, whichever is less.” (See also Section 1121)
IFC Section 606.8 “Machinery rooms shall contain a refrigerant detector with an audible and visual alarm… The alarm shall be actuated at a value not greater than the corresponding TLV-TWA values shown in the International Mechanical Code for the refrigerant classification.”
IIAR-2 Section 13.2.3.1 “One detector shall be utilized to activate an alarm…at a value not greater than the corresponding TLV-TWA;” and Section 13.2.1.2 “The detectors shall activate visual and audible alarms inside the refrigerating machinery room and outside each entrance to the refrigerating machinery room.”
On the topic of alarm initiation, the codes and standards are prescriptive and are in general agreement that an alarm signal should be initiated at the TLV-TWA concentration (the text “or consistent therewith” in the UMC gets you there), which is 25 ppm for ammonia. The TLV-TWA value represents the concentration of refrigerant in air to which nearly all workers could be repeatedly exposed for an 8-hour workday and a 40-hour workweek without adverse effects. This is not truly a hazardous concentration, but instead a warning that is given to signal the potential for a hazardous condition to develop.
On the topic of alarm notification devices, things aren’t quite so good. All of the documents cited above require audible and visual alarms, and ASHRAE 15, the UMC and IIAR-2 all specify that alarm devices must be provided inside the machinery room and outside each entrance to the machinery room. This implies a single audible and visual device at each location mentioned, but the purpose of the alarm signal is not specified.
Some interpret the intent of the alarm signal to be notifying a responsible individual, but jurisdictions have reportedly interpreted the requirements as mandating an occupant evacuation alarm system, complete with visual devices that comply with the Americans with Disabilities Act (ADA), just as is required for fire alarm systems. In addition, some jurisdictions have reportedly asked for the TLV-TWA alarm to notify the fire department as a basis for initiating an emergency response. All of this is further complicated by the complete lack of guidance with respect to how ammonia detectors required in refrigerated process and storage areas should be handled. That perspective isn’t mentioned in any code or standard.
Given that the TLV-TWA concentration does not indicate an imminently hazardous condition, or necessarily an impending hazardous concentration, initiating an evacuation or emergency response at this concentration seems excessive. Certainly, the guidance in ASHRAE 15 Appendix F does not support such an interpretation. Instead, it is evident that the intent of refrigerant leak detection alarms is to gain the attention of a responsible party to have the situation investigated. In the case of ammonia, an increasing hazard level will become clearly evident based on an increasingly untenable odor level.
Before ending this discussion, it’s worth noting that ammonia was entirely exempted from leak detection and alarm requirements in previous editions of codes and standards because it was accepted that ammonia’s odor provided adequate warning of a release. For example, consider that the IFC didn’t begin requiring leak detection for ammonia refrigeration until the 2006 edition; although, IIAR-2 and ASHRAE 15 included the requirement prior to that. If you are dealing with an existing facility that was built under a previous code, it’s important to research the regulations that governed at the time to determine applicable requirements, recognizing that current code requirements for leak detection and alarms are not retroactive to existing facilities.
In conclusion, there is no doubt that codes and standards could benefit from revisions that would clarify their intent and avoid widely ranging interpretations on the topics discussed in this article and others that are related. A task group working on behalf of IIAR’s code and standards committees is taking a closer look at regulations for refrigerant detection alarm systems and will be making recommendations on options to address these issues. The work of this task group is important because IIAR is the best organization to determine appropriate regulations for ammonia leak detection systems. If these issues aren’t addressed by IIAR, it seems likely that another organization will eventually step in to dictate a solution. IIAR will have to bear in mind that the issues being dealt with go beyond ammonia and solutions may eventually impact leak detection requirements for other refrigerants. Thereby, we welcome input from anyone with an interest or expertise in the subject.
