Fire Side Chat: NFPA 72 Requirements for Installing Gas Detection Systems on Fire Alarms
SSI columnist Shane Clary dives into the details of NFPA 72.
While NFPA 72, The National Fire Alarm and Signaling Code, is primarily for the installation of fire alarm systems, the standard is intended for other critical uses. One of these is for detection of environmental changes and in particular hazardous gases.
Currently CO systems are addressed in NFPA 720, Standard for the Installation of Carbon Monoxide (CO) Detection and Warning Equipment. I have discussed aspects of this standard in past Fire Side Chats. The detection of other gases is still found within NFPA 72. This is one of the reasons the NFPA Standards Council has approved the request of the NFPA 72 Correlating Committee to begin work to move the requirements for CO detection that are now found within NFPA 720 to NFPA 72. A task group of members of both standards is working toward this end.
Let’s take a look at the verbiage of what’s covered in NFPA 72. In Chapter 17, Initiating Devices in the 2016 edition, Section 17.10 Gas Detection is not a large section:
17.10.1 General. The purpose and scope of Section 17.10 shall be to provide requirements for the selection, installation and operation of gas detectors.
17.10.2 Gas Characteristics and Detector Selection.
22.214.171.124 Gas detection equipment shall be listed for the specific gas or vapor it is intended to detect.
126.96.36.199 Any gas detection systems installed on a fire alarm system shall comply with all the applicable requirements of Chapters 1, 10, 14, 17 and 23 of this Code.
188.8.131.52 The requirements of this Code shall not apply to gas detection systems used solely for process control.
184.108.40.206* The selection and placement of the gas detectors shall be based on an engineering evaluation.
A.220.127.116.11 (from Annex A) The engineering evaluation should include, but is not limited to, the following:
- Structural features, size and shape of the rooms and bays
- Occupancy and uses of areas
- Ceiling heights
- Ceiling shape, surface, and obstructions
- Ambient environment
- Gas characteristics of the gases present
- Configuration of the contents in the area to be protected
- Response time(s)
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The Technical Committee on Initiating Devices realized that there are different types of gases that can be and are detected. Rather than provide the requirements for each, the group decided to offer more of a performance-based approach. The designer is to perform an engineering evaluation, to be based on the nine points as outlined above.
The designer should also follow the manufacturer’s printed instructions. As an engineering evaluation is required, this should be left for a fire protection engineer to perform and designate the locations where the detectors are to be installed. I caution that a contractor should not be performing an engineering evaluation without the proper training and education.
Typically a fire alarm system will monitor the outputs from systems that have been installed by others who specialize in these areas. Typical gases and vapors that I have seen being detected are: ammonia, nitrogen, oxygen, silane, phosphine, carbon dioxide, sulfuric acid, chlorine, hydrochloric acid and cyanide.
When a fire alarm system is connected to one of these detection systems, or if that system is being installed standalone, the notification appliance cannot state “Fire” or “Fire Alarm.” The notification appliances must be different – typically these may be blue, amber or some other color – and produce a different sound.
The AHJ should be consulted as to how any signal from these systems is to be acted upon. Depending on the gas or vapor, the department may wish to be notified as an alarm event, a supervisory event or just notify a responsible party.
NFPA 72 also has provisions for the monitoring of temperature extremes within a building to help prevent a fire sprinkler suppression system from freezing and includes:
17.16.4 Water Temperature Supervisory Signal-Initiating Device.
18.104.22.168 A temperature supervisory device for a water storage container exposed to freezing conditions shall initiate two separate and distinctive signals, as specified in 22.214.171.124.
126.96.36.199 One signal shall indicate a decrease in water temperature to 40Â° F (4.4Â° C), and the other shall indicate its restoration to above 40Â° F (4.4Â° C).
17.16.5 Room Temperature Supervisory Signal-Initiating Device. A room temperature supervisory device shall indicate a decrease in room temperature to 40Â° F (4.4Â° C) and its restoration to above 40Â° F (4.4Â° C).
You may be asked to supervise other environmental signals, such as a critical freezer or refrigeration unit. Approval from the AHJ would be needed first as this would reflect a combination system as defined by NFPA 72. Any fault on these connections would need to be isolated so as to not affect the fire alarm system.
So as you can see, NFPA 72 covers more than just your standard fire alarm system – specifically, many potential hazards that you cannot see.
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