In the interest of reducing costs and meeting more stringent environmental regulations, fleet operators – both public and private – are shifting their fleets from gasoline/diesel power to alternative fuels such as natural gas, propane and hydrogen.
With the introduction of these new fuels, the fueling stations and maintenance facilities usually need to be modernized to include gas detection. At the maintenance facilities, the potential risk lies with the vehicles themselves that contain the fuel, but at the fueling stations, the dangers could be the vehicles or the storage areas and fueling equipment.
Maintenance facilities require gas and flame detectors in areas where the alternative-fuel vehicle could be located, such as the work bay, paint shop, chassis wash, tire shop, fueling area, dynamometer building or the gas compressor area. The International Fire Code and numerous National Fire Protection Association (NFPA) codes often are applicable in these applications. In addition to the standard safety requirements established by the local fire department or fire codes, most facilities require various agency approvals for the gas detection system placed in these areas.
The gas sensors and control system normally need performance approvals from certified nationally recognized testing laboratories (NRTL) like FM, CSA or UL. The monitoring philosophy is designed to react to the hazardous gas leak by providing dispersion and dilution with ventilation. They also require control and management of any potential ignition source near the location of the accidental discharge of gas.
What Are Alternative Fuels?
There are three major types of alternative fuels: natural gas, propane and hydrogen. In their natural state, these fuel types are odorless, colorless and tasteless. Natural gas and propane can be odorized with mercaptan, which is a sulfur-like compound that allows leaks to be detected by the human nose.
Natural gas consists of primarily methane with some other trace compounds. It is lighter than air with a relative gas density of about 60 percent that of air. This means when there is a release of this gas in an enclosed space, it will migrate to the highest point in the room. The explosive range of methane is 5 to 15 percent by volume when mixed with air, so it will take at least 5 percent methane concentration in a room to become explosive. This 5 percent methane gas concentration is 100 percent of the lower explosive limit (LEL). The 100 percent LEL point is where there is enough fuel and air mixture present to cause a fire or explosion.
Natural gas can be found in two forms for transportation: compressed natural gas (CNG) and liquefied natural gas (LNG). CNG primarily is methane, compressed up to 5,000 PSIG at normal temperature. CNG’s storage tanks are specialized pressure vessels and require certification for use. Storage tanks on a vehicle may be located on top, on the frame side or behind the cab.
LNG is pure methane stored at atmospheric pressure, but refrigerated to minus 260 F, which changes the gas to a liquid state. It requires smaller storage containers than CNG, but these storage vessels also are specialized – like a thermos bottle – to keep the fuel at a low temperature and in a liquid state. CNG more commonly is used for short-haul vehicles while LNG more often is used in long-haul vehicles.
Hydrogen (H2) also is lighter than air, with a relative gas density of only 7 percent of air. It also will seek the highest point if released in an enclosed area. It has a much larger explosive range, from 4 percent by volume (100 percent LEL) to 75 percent by volume. It is a manufactured fuel and is stored at pressures of 8,000 PSIG to 10,000 PSIG. As a manufactured fuel, it is used in two applications: as the catalyst in a fuel cell or as a motor fuel. There are not many hydrogen vehicles in use today.
Liquefied petroleum gas (LPG) or propane is a heavier-than-air gas, and has a relative gas density of about 150 percent of air. It will migrate to grade level and seek low spaces for collection. LPG typically is odorized to make it smell and has a small explosive range from 2 percent by volume (100 percent LEL) to around 10 percent by volume. As a transportation fuel, it is very good and quite prevalent. It also is a manufactured fuel requiring specialize storage vessels and handling techniques.
Codes and Regulations
Alternative-fuel vehicle maintenance and refueling facilities are regulated by international, national and local regulations. The primary standards that are important for the facility design are provided by NFPA and International Codes Council (ICC). The local authority having jurisdiction (LAHJ or AHJ) is the regulatory agent that may adopt or expand on these codes and determine which regulations are applicable to the facility.
One of the key codes that affect an alternative-fuel vehicle maintenance facility is the International Fire Code, IFC 2012. IFC 2012 specifies:
2311.7.1.1 Design. Ventilation shall be by a continuous mechanical ventilation system or by a mechanical ventilation system activated by a continuously monitoring natural gas detection system or, for hydrogen, a continuously monitoring flammable gas detection system, each activating at a gas concentration of not more than 25 percent of the lower flammable limit (LFL). In all cases, the system shall shut down the fueling system in the event of failure of the ventilation system.
2311.7.2 Gas detection system. Repair garages used for repair of vehicles fueled by non-odorized gases, such as hydrogen and non-odorized LNG, shall be provided with a flammable gas detection system.
2311.7.2.1 System design. The flammable gas detection system shall be listed or approved and shall be calibrated to the types of fuels or gases used by vehicles to be repaired. The gas detection system shall be designed to activate when the level of flammable gas exceeds 25 percent of the lower flammable limit (LFL). Gas detection shall also be provided in lubrication or chassis service pits of repair garages used for repairing non-odorized LNG-fueled vehicles.
2311.7.2.2 Operation. Activation of the gas detection system shall result in all the following:
- Initiation of distinct audible and visual alarm signals in the repair garage.
- Deactivation of all heating systems located in the repair garage.
- Activation of the mechanical ventilation system, when the system is interlocked with gas detection.
Other key codes that affect an alternative-fuel vehicle maintenance facility include:
• NFPA 30A (2012) Motor Fuel Dispensing Facilities and Repair Garages
• NFPA 52 (2013) Vehicle Gaseous Fuel
Systems Code
• NFPA 88A (2011) Standards for
Parking Structures
• NFPA 70 2014 National Electric Code
• NFPA 59A 2013 Standard for the
Production, Storage and Handling of LNG
Note that the ICC and NFPA codes, if adopted by states, are voluntary and enforced by the local authority having jurisdiction. Additional codes may be referenced during the development of the LAHJ requirements.
Design Considerations
When designing the facility, it is important to take into considerations various design requirements based upon the codes and regulations. It also is necessary to determine the scope of work being conducted in the facility. Whether major or minor work is being performed is relevant regarding the codes; however, they are not particularly clear on the definition of major vs. minor work. It is up to the AHJ to decide. One AHJ stated that if it takes a wrench, it is considered major service!
Also take into consideration the layout of the environment such as:
• How open is the building?
• What natural ventilation exists?
• What other structures and buildings surround the building?
• What is the security of the building?
• What ignition sources exist in the building?
Finally, you need to consider the geographic area and climate factors. Constant heating, ventilation and air conditioning of any building could result in high energy costs during the winter and summer months.
Gas Detection
The two primary choices for gas detection are portable detectors and fixed detectors. The codes call for the gas detection system to do the following:
• Automatically alarm and notify;
• Deactivate heating systems;
• Activate ventilation systems.
Based on those criteria, the only answer for a maintenance facility is a fixed gas-detection system. A controller-based gas-detection system has the advantages of control and interface from a single point with minimal wiring costs, simpler calibration and the ability to have third-party approval for the complete system.
Controller-based systems give the operator greater control over the operation by being able to perform different control operations for different zones and having a central point to view detector functionality.
Due to the extensive codes and regulations involved in this situation, it is necessary that the sensors have third-party NRTL approval (in particular, Factory Mutual (FM) approval). In addition, many AHJs require not only third-party approval for operation in hazardous locations, but also performance approval showing that the sensors and control system operate according to code and specification.
Remember that NFPA 30A states that in an alternative-fuel vehicle facility, the top 18 inches of ceiling area are considered to be a Class 1, Division 2 hazardous area. So FM approval becomes mandatory for sensors located in this area.
There are two types of sensors used to monitor for combustible gases. A catalytic bead-type sensor can monitor for both natural gas and hydrogen. An infrared sensor can monitor for natural gas, but not hydrogen. The calibration frequency for infrared sensors tends to be longer duration, and as a result they require lower maintenance. Both sensor types should have FM approvals.
When installing gas sensors, be sure to mount them in the proper locations as specified by your design engineer and AHJ. Remember that natural gas and hydrogen are lighter than air so their sensors should be mounted close to the ceiling. Propane is heavier than air and thus the sensors must be mounted closer to the ground. Use common sense in determining mounting locations, like mounting the sensor between the obvious source of the gas and the source of ignition, and not directly in front of the ventilation fan.
Code requirements call for alarms when the hazardous gas reaches 25 percent LEL of the combustible level. The visual alarm must be visible from all points and the audible alarm heard by all people. The alert devices also must be ADA compliant. Working with the AHJ will determine the proper evacuation and “safe to return” policies. (Note that audible and visual alarms are not the same as a fire alarm. Auto dialers also be may installed where required.)
Mitigation
Mitigation is the effort to reduce loss of life and property by lessening the impact of the hazardous situation. The key mitigation for a release of combustible gas in a maintenance facility is to remove the gas.
This usually is performed by proper and powerful ventilation. Under normal situations, there should be a natural draft of air flow occurring. The office areas typically will have a higher pressurization to prevent the entrance of hazardous and toxic fumes into a compact area. The designer of the ventilation system needs to make sure that make-up air is available either via the HVAC system or doors and vents.
Most proper ventilation systems utilize a “push/pull” design with air-handling units pushing air into the building and exhaust fans pulling the air from the building and exhausting to the atmosphere. Normal day-to-day operation will have the fans on low speed to continuously refresh the air. During emergency situations when activated by the gas detection system, the ventilation system increases the air flow to change the volume of air eight times each 60 minutes, which is about 45 percent more than normal volume.
It is important that management realizes that the refueling and maintenance facility requirements will be different for alternative-fuel vehicles. It also is vital that project planners take into consideration the type of fuel being used, use of the facility, local and national regulatory requirements, safety of the people and property, alarm and notification requirements, ventilation requirements and the total cost of ownership.
Corey Miller is an alternative-fuel market specialist with Sierra Monitor Corp. He has over 28 years of experience with measurement instrumentation and systems, and 15 years specializing in alternative-fuel monitoring solutions.