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Maintenance Shop Modification & Service

Whether you are a new or used truck dealer and service provider, or you’re a fleet that does TRAC leases or you buy and maintain some or all of your own vehicles, special considerations must be taken when thinking about where and how you are going to provide or get supplied with service for your CNG vehicles.

Midwest Energy Solutions is a certified and licensed general contractor (“GC”) to support our primary business of building CNG station infrastructure. We have worked with several local fire marshals to investigate, design and approve modifications required to do service work on CNG vehicles. MWES provides consulting services to fleets to identify potential maintenance shop issues and possible options to comply with local safety codes. Write to us [click here to go to “contact us” page] and let us know what you are considering in the way of a shop modification and we’ll see if we can help you.

Maintenance shop modification is especially important because in existing gasoline and Diesel shops, you must accommodate a liquid fuel that is combustible and one that puddles on the ground has to be prevented from leaking into a floor drain. So too do you need to accommodate a fuel that is combustible and one that, when exposed to the open air, rises to the highest point above the source or released gas where it can accumulate and become a hazard.

The following are excerpts from a recent technical paper written by Leo Thomason, Executive Director, Natural Gas Vehicle Institute (NGVi) who summarizes CNG maintenance shop considerations very well:


While there are others that must be considered due to site-specific details, there are four primary fire codes covering CNG vehicle maintenance facilities including National Fire Protection Association (NFPA) 52 Vehicular Gaseous Fuel Systems Code, 70 National Electrical Code and 30A Code for Motor Fuel Dispensing Facilities and Repair Garages and the International Fire Code. These codes address ventilation, lighting, heating, electrical, and internal mechanical building structural systems of vehicle maintenance facilities that work on CNG vehicles.


Existing vehicle maintenance or repair facilities have been designed to meet safety code requirements for gasoline and/or diesel, and both the liquid and the vapors for these fuels are heavier than air. Thus, the code requirements address the needs of heavier-than-air fuels. Because there are no “standard vehicle maintenance facilities”, the codes must be applied based on the unique characteristics of each facility. Just one example of the major differences in these codes is reflected in the defined hazardous areas. In gasoline/diesel vehicle maintenance facilities, the defined hazardous area is from the floor 18 inches up. There cannot be any ignition sources in this space. Typically, the ventilation flow in these facilities is introduced at the ceiling level and exhausted at or near floor level.

Conversely, since natural gas is lighter than air, the defined hazardous area in NGV maintenance facilities is from the ceiling 18 inches down. There can be no ignition sources within this defined space, which is the opposite of the design for most existing gasoline/diesel vehicle maintenance facilities. In addition, the ventilation flow in natural gas vehicle facilities should be introduced at the floor and exhausted at or near the ceiling. These are just two examples of the many differences in code requirements for facilities designed for liquid fuels vs. facilities designed to accommodate lighter-than-air fuels.


What NGV dealers and/or fleet managers must understand is that even if a natural gas powered vehicle requires routine maintenance such as an oil change or tire rotation, the maintenance facility must be able to safely accommodate the lighter-than-air fuel. There are possibly administrative procedures that can be implemented to accommodate maintenance and repair of the non-CNG fuel system components. For example, a CNG powered vehicle may typically be parked inside an unmodified maintenance facility for non-CNG fuel system maintenance under certain circumstances and conditions. The CNG fuel system is defined as any components from the fuel receptacle up to and including the fuel injectors). These conditions include procedures such as leak checking the vehicle before it is brought into the facility, turning off the fuel supply, ensuring adequate ventilation is present and ensuring that there are vehicle technicians inside the facility as long as the vehicle is parked inside the facility.

Without proper modification of the facility, CNG-powered vehicles should not be parked inside the maintenance facility overnight and/or when no technicians are present. More importantly, the CNG fuel system cannot be maintained or repaired inside any maintenance facility that has not been modified to accommodate lighter-than-air fuel.

A study and report should include:

  1. Gather and document pertinent engineering information regarding the existing building in sufficient detail to allow for the design of necessary upgrades.
  2. Size and select required major equipment and gather pertinent vendor information.
  3. Develop preliminary conceptual layout drawing to generally describe proposed upgrades and space utilization.
  4. Contact local building and fire code officials to confirm documentation requirements for formal submittal to approve the plan.
  5. Develop design drawings, calculations, and details describing work required to upgrade the existing facility in sufficient detail to allow for preliminary estimating and project planning.
  6. Review and respond to relevant technical questions.
  7. Supervise modification tasks.
  8. Confirm completed construction was performed compliant with design.
  9. Record drawing and close out project.
  10. Update design drawing set and issue final record of drawings. Confirm successful start-up and testing of new systems and final sign off of all permits obtained.


Because every maintenance facility is different, the cost to modify one to accommodate CNG vehicles varies considerably depending on size of the facility and the modifications that must be undertaken. The best place to start is for CNG vehicle dealers and shops to become knowledgeable enough about the codes to be able to evaluate the recommended modifications. Understanding that safety is the most important criteria of any maintenance facility, there can be a huge cost range between making the reasonable modifications that are required by code vs. making every modification possible vs. optimizing all factors into the best solution.

Write to us and let us know how we can help your investigation and serve your needs.