The primary functions of a combustible gas detection and alarm system are to: A gas detection and alarm system is strongly recommended for a number of reasons. It greatly enhances personnel safety and property protection, • Provide early warning to occupants that a methane gas release has occurred and the facility’s insurance underwriter may require the installation of such a system. • Initiate actions to eliminate potential ignition sources Gas Detection, Alarm, and Control Systems • Initiate actions to promote quick dilution of the concentrated gas to levels below the LFL.
The applicable codes and regulations require that any facility that maintains vehicles that use non-odorized gas fuel be equipped with a flammable gas detection system. For example, NFPA 30A includes the following requirements: Types of Combustible Gas Detectors There are several types of combustible gas detectors, the most common being catalytic bead and infrared. Using catalytic bead detectors typically lowers capital cost because fewer detectors are needed but are not recom mended because they require more frequent calibration and have a shorter life before internal components must be replaced.
Infrared detectors, which are used most widely within the industry, are available as either a point- type monitor or an open-path design. Point-type detec tors detect an LCL level at a given point of the ceiling, whereas open path units detect an overall presence of gas within the beam. Open path detectors can reduce capital and maintenance costs in large garages, but typically require the use of some additional point-type detectors. There is no universally best approach, and the design of the system should be performed by a registered/licensed engineer in collaboration with the system manufacturer. A typical point-type infrared detector head is displayed in Figure 28.
• The flammable gas detection system must be cali brated to the type of fuel being used, and the system must be activated when a concentration of 25% of the LFL is detected. • Upon gas detection, the system must activate audible and visual alarms, deactivate the heating system(s) and turn on the ventilation system. • If a failure occurs within the gas detection system, the system must automatically deactivate the heating system(s), activate the ventilation system, and activate an audible trouble signal in a location approved by the AHJ. A combustible gas detection and alarm system will:
• Provide early warning to occupants • Initiate actions to eliminate potential ignition sources • Initiate actions to promote quick dilution of the gas. The applicable codes suggest, but do not categorically state, that a gas detection system is not required for a facility that maintains vehicles that use odorized gas fuel such as CNG. But industry experience has shown that AHJs generally require a gas detection system despite the apparent exemption within NFPA 30A. A gas detec tion and alarm system is strongly recommended for a number of reasons. It greatly enhances personnel safety as well as property protection.
In addition, the facility’s insurance underwriter may require the installation of such a system. Figure 28. Typical infrared combustible gas detection head. Photo from Gladstein, Neandross & Associates, NREL 44692 SEPTEMBER 2017 19