Upgrading Your Vehicle Maintenance and Repair Facility for NGVs Series (Part 4 of 5): Ventilation and Methane Detection

By Annalloyd Thomason, Vice President/General Manager, NGVi 

Adequate ventilation in a natural gas vehicle maintenance facility is critical. It ensures that in the event of a leak, there is an effective system in place to remove leaking gas and bring fresh air into the facility in a very short period of time. It helps prevent an ignitable mixture of natural gas from accumulating inside the maintenance facility in the event of a leak, and helps keep technicians and other employees working in the building, safe.

What exactly are the code requirements for ventilation in a maintenance facility where NGV fuel system repairs are made?

Code Requirements
While National Fire Protection Association (NFPA) 30A does not specify requirements for ventilation for NGV repair facilities, the International Fire Code (IFC) requires continuous mechanical ventilation of major repair facilities at the rate of five air changes per hour. Where natural ventilation can meet this criterion, the authority having jurisdiction (AHJ) must approve its use. Additionally, the IFC provides two exceptions to the continuous ventilation rule: (1) when the ventilation is interlocked to and controlled by a methane gas detection system; or (2) the ventilation system is interlocked to the lighting system for the facility.

Most existing maintenance facilities will have a ventilation system of some type—including gravity ventilators, a make-up air system or a dedicated heating/ventilation/air conditioning (HVAC) system. Some current ventilation systems may be able to meet the code requirements for ventilation in CNG and LNG vehicle maintenance facilities, provided they (1) are capable to provide ¾ to 1 cubic foot per minute of air flow per square foot of floor space; (2) operate continuously; or (3) are interlocked to the lighting system or a methane detection system.

While continuous ventilation using an existing system sounds like the easiest option, it is possibly the most expensive. The cost of continuously running an existing HVAC system that provides heat in winter or air conditioning in summer can be costly—especially in climates with very cold winters and/or very hot summers.

Methane Detection Systems
Currently, the most widely used option to ensure proper ventilation is to install a methane detection system in the NGV repair facility that is interlocked to a power exhaust system—which means the exhaust system is only engaged if the methane detection system detects gas at 25% of the lower flammability limit. There is no code requirement for methane detection systems in CNG maintenance facilities because CNG is odorized, yet it is the most frequently used solution.For LNG maintenance facilities, methane detection is required because LNG is an unodorized fuel and unlike CNG, human detection of LNG is not possible. Code requires that methane detection systems in LNG facilities must be interlocked with the ventilation system.

Methane detection systems must be listed in accordance with UL 2075 or approved by the AHJ. In addition, they must activate at 25% of the lower flammability limit (1.25% concentration in air) for natural gas. Methane detection systems are also required to activate the mechanical ventilation system, deactivate heating systems and initiate an audible and visual alarm inside the facility.

If the methane detection system itself fails, it is required to activate the ventilation system, deactivate all heating systems inside the facility and initiate a trouble alarm in an approved location. Methane detection systems are required to be tested and calibrated according to the manufacturer’s guidelines and approved by the AHJ.

A final and important note: if you choose methane detection systems as your ventilation solution, make sure the methane detection system in your facility is designed by an engineer with expertise in these systems installed in NGV maintenance facilities. This will help ensure that the system is designed specifically to the needs and requirements of your facility.

Ventilation in Pits
Existing codes do not contain any additional requirements for ventilation in pits for CNG maintenance facilities—primarily because natural gas is lighter than air and rises when it leaks. However, both NFPA 30A and the IFC require methane detection systems in below-grade pits in LNG maintenance facilities.

In our final installment in this series, we will discuss maintenance facilities modifications and practices when performing welding and hot work.


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