IFC Ventilation Requirements The IFC states that major repair garages shall be ven tilated at a rate of one cubic foot per minute (cfm) for every 12 cubic feet of structural space, which is equiva lent to five air changes per hour (ACH). Note that this calculation is based on the total volume of the structure, not the square footage of the floor or ceiling. Further more, the IFC provides three options for controlling ventilation: 1) continuously, 2) continuously while the space is occupied via interconnection with the lighting circuit, or 3) upon demand for dilution ventilation triggered by the gas detection system. Figure 7. A pass-through window presents a potential path of migration.
Photo courtesy of Gladstein, Neandross & Associates, NREL 44902 The potential energy impacts of continuous operation and tempering of the entire volume of air in a structure influences the design of many maintenance facilities, particularly those in cold climates. For this reason, a maintenance facility manager may elect to use methane detection as the triggering mechanism instead of con tinuous ventilation. This method incurs similar installa tion costs but results in greatly reduced operating costs. Various approaches to ventilation system design and installation of methane detection systems are discussed later in this section. for ventilating a maintenance facility.
Naturally, ventila tion is necessary to quickly and effectively dilute released natural gas so that the gas concentration is below the combustible level. However, ventilation is also necessary to direct gas to the detection and alarm systems that will alert occupants to safely evacuate the facility. Lastly, ven tilation aids in preventing the gas from accumulating near potential ignition sources. NFPA 30A Ventilation Requirements Ventilation effectiveness under NFPA 30A is also based on the total volume of the structure. However, it focuses on potential electrical sources of ignition within the area 18 inches below the ceiling. This area is classified as Class I, Division 2.
NFPA 30A states that electrical devices located in this zone do not need to meet Class I, Division 2 specification if the structure has an effective continuous ventilation rate of at least 4 ACH. If the structure does not have this continuous ventilation rate, existing electrical devices that do not meet the Class I, Division 2 specification must be relocated to below this 18-inch zone or replaced with electrical devices rated for Class I, Division 2 service. The IFC and NFPA differ in their calculations and control strategies. Knowing which code requirements the local governing body follows is critical to determining which control strategy should be implemented.
Unfortunately, ventilation volumes and strategies are one area where the codes differ significantly. All agree that natural ventilation may be allowed at the discretion of the AHJ. However, if the AHJ elects to require mechanical ventilation, the IFC and NFPA differ in their calculations and control strategies. Knowing which code requirements the local governing body follows is critical to determining which control strategy should be implemented. NFPA 30A does not specifically address operational parameters of ventilation systems in major repair garages.
Generally, fire marshals and other AHJs tend to refer to the IFC operational guidelines of 1) continu ous operation, 2) continuous operations while occupied, via interlock with lighting, or 3) methane detection system-triggered. If the third operational parameter is selected, then all electrical devices in the “ceiling zone” must be removed, relocated, or replaced with devices rated for Class I, Division 2 applications. Ventilation is necessary to quickly and effectively dilute released natural gas. It is also necessary to direct gas to the detection and alarm systems and prevent it from accumulating near potential ignition sources. SEPTEMBER 2017 11