In the International Fire Code, Section 606 – Mechanical Refrigeration has two distinct requirements regarding the refrigerant detector(s) and their alarm signal and in both requirements, the phrase “approved location” is used. In one case, they are talking about the location of the actual refrigerant detector/sensor, and in the other case, they are talking about where the detection alarm will be sounded. In the case of ammonia refrigeration systems, the engine/machinery room is often UNOCCUPIED, and therefore these detection systems play a KEY role in identifying leaks very early. But this relies on the detectors being placed in the proper area(s) AND the alarm(s) sounding in a way that it can be received and responded to. Section 606.8 Refrigerant Detector states:
606.8 Refrigerant detector. Machinery rooms shall contain a refrigerant detector with an audible and visual alarm. The detector, or a sampling tube that draws air to the detector, shall be located in an area where refrigerant from a leak will concentrate. 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. Detectors and alarms shall be placed in approved locations. The detector shall transmit a signal to an approved location.
It is the last two (2) sentences that I want to discuss.
Detectors and alarms shall be placed in “approved locations.”
The detector shall transmit a signal to an “approved location.”
In order to fully understand the requirements of Section 606.8, we have to cross-reference to Section 1105.3 of the International Mechanical Code (IMC) for refrigerant detector requirements. Engine/Machinery rooms are required by the IMC (since I have been in safety) where refrigerant quantities exceed the specified limits found in Table 1103.1 of the IMC.
Detector location is critical to early leakage warning and should comply with the detector manufacturer’s instructions. The required detectors must be designed for application with the refrigerant or refrigerants used in the machinery room.
Because machinery rooms are unattended most of the time, once the refrigerant gas is detected at the levels noted in section 606.8, a local alarm must be initiated and a signal must be transmitted to an “approved location” REMOTE from the engine/machinery room, possibly to refrigeration technician via pager or cell phone.
The alarm is intended to alert those BOTH inside the area of detection and in the immediate vicinity to prevent harm to those outside the area of release. The notification to an approved location provides timely information to those who must take a role in emergency response, whereas the local alarm is a warning for those in the vicinity of the release.
As a first step in the mitigation of the hazards of fugitive refrigerant gas, the required detectors have the additional important role of activating the emergency ventilation/exhaust systems in the machinery rooms required by Sections 1105.6.3 and 1106.3 of the IMC (see the definition of “Machinery room” and Table 1103.1, both in the IMC).
For those of you that have a PSM/RMP “covered process,” these “approved locations” are CRITICAL to your process safety efforts and such become a secure location. This means that BOTH the “approved location” of the detectors and the “approved location” of the alarm signal from those detectors are a fundamental part of your PSM/RMP management system and any changes to either “approved location” would need to be managed using the facility’s Management of Change program. This includes managing the “cell phones” carried by the refrigeration technicians to ensure the phone numbers in the call-out system are updated when personnel change (another great reason to do MOCs on personnel changes).
As for the “approved location” of the detectors, that is a whole other can of worms. Most of the AHJ’s I work with will tell you that refrigerant detector locations must be carefully considered. Most refrigerants (but not Ammonia) are heavier than air, making floor depressions and pits natural areas for accumulation. But the key to accurately locating a detector in the machinery room is to remember that occupant safety is the primary objective, and the danger is in breathing refrigerant. Placing the sensor below the common breathing height of 5 feet results in an additional safety margin because all commonly used halocarbon refrigerants are three to five times heavier than air. PLEASE NOTE that Anhydrous Ammonia gas is LIGHTER THAN AIR and would need to be at the ceiling or air stream around ceiling fans.
When undistributed by airflow, escaping refrigerant will flow to the floor, seeking the lowest levels and filling the room from the bottom up. Because pits, stairwells or trenches are likely to fill with refrigerant first, detectors should also be placed in any of these areas that may be occupied. The last column of Table 1103.1 dictates the alarm actuation threshold.
Detector manufacturers’ will provide installation guidance for the location of detectors and the required number of sensors for any given room size. Because most general machinery rooms are unoccupied for extended periods, a refrigeration leak may go undetected, allowing a buildup of refrigerant that can pose a threat to the building occupants and the maintenance personnel who will be required to enter the machinery room.
The ACGIH defines three (3) levels of refrigerant exposure:
Level 1 is the AEL, which is the level at which a person can be exposed for 8 hours per day for 40 hours per week without hurting health.
Level 2 is the STEL, which is defined as three times the AEL. At this level, a person should not be exposed for more than 30 minutes at a time. Persons working in a machinery room having this concentration of refrigerant should be equipped with respiratory protection.
Level 3 is the emergency exposure limit (EEL). At this level, persons should not be in the room at all without a self-contained breathing apparatus.
Early detection of leaking refrigerant depends on the location of the refrigerant detectors. If they are improperly located, a refrigerant leak could go undetected for an undesirable length of time, thus allowing a significant amount of refrigerant to escape.
Items to be considered when choosing locations for detectors are the airflow patterns of the room, the particular refrigerant density and the fact that the primary hazard to the occupants is inhalation. The sensors should be located to PREVENT the standard ventilation system from interfering with detection. Placing detectors between the refrigeration system and exhaust fan inlets should help to ensure that the presence of refrigerant will be detected.
Depending on the size of the machinery room and the number and type of refrigeration systems, more than one detector may be necessary. Manufacturers’ installation instructions for the refrigeration detection system should be followed when choosing the location and the number of sensors for a particular machinery room application. For example, many refrigerant detection systems are capable of activating a warning system with a warning light, alarm or similar device if refrigerant exceeds a preset concentration or level due to a leak. Typically, the warning systems can alert people inside and outside the machinery room so that the leak can be quickly located and repaired.