By Marc Burrell, Project Engineer, NGVi
It’s no secret the benefits that natural gas vehicles (NGVs) offer, such as reduced fuel costs, quieter engine operation, no after-exhaust treatment, and reduced emissions. Less known, however, is the fact that nearly all existing vehicle maintenance and repair facilities (VMFs) that were originally designed for gasoline or diesel vehicles will require modifications to allow technicians to safely work on compressed (CNG) or liquefied (LNG)-powered vehicles.
Whether your involvement in NGV maintenance and repair is as a vehicle dealer, an independent repair facility or an NGV fleet manager, the starting place is to understand what modifications are necessary to make your facility safe to park, maintain and repair NGVs. This five-part series will introduce you in greater detail to the vehicle maintenance facility requirements for NGVs, and to the components of the facility that must be evaluated and may require modification.
Before we begin, let’s clarify a common misconception about VMF evaluations. We are often asked, “Can’t you just send us a checklist so we can teach our facilities managers to do this ourselves?” Unfortunately, the answer is no, and here is why. Each facility is unique, and effectively applying the multiple codes that must be complied with requires an individual and unique evaluation by a knowledgeable and experienced professional—one who is extremely familiar with the codes and industry best practices. We can’t stress this enough.
During a VMF evaluation, several aspects of the facility are carefully assessed for potential hazards, which will likely not be permitted by the local fire marshal, who is typically the authority having jurisdiction (AHJ) over VMF modifications. The parts of the VMF that will be discussed in this five-part series include the building envelope, heating, ventilation, lighting, and electrical systems. This month’s portion of the series will look at the building envelope.
The building envelope consists of the exterior and interior walls, roof, structural members, and parts of the building adjacent to the vehicle service area, such as offices, classrooms, restrooms/personal locker areas, or parts rooms. Paraphrasing one of the codes, areas where CNG-powered vehicles are stored, maintained and/or repaired should prevent natural gas from reaching other parts of the building. In layman’s terms, in the unlikely event of a natural gas leak, you don’t want gas to collect into a combustible mixture within any part of the building, especially outside of the vehicle service area.
Since all of the codes are performance based, there can be multiple ways to make the building envelope code compliant. Each building is different, and factors—such as the construction practices and the age of the building—demand special consideration. This makes achieving the desired result specified by the various codes for each building quite challenging. Let’s begin by looking at the walls.
One of the main concerns is the interior walls. If an interior wall separates the vehicle service area from another room in the facility, it should be solid, with no way for gas to penetrate the wall or leak into the room around an unsealed edge, i.e., between the ceiling and the top of the wall. Some walls have features that require special attention. The simple ones are doors and windows, which frequently open to the vehicle service area. While this is an acceptable practice in VMFs where gasoline and diesel vehicles are repaired, doors and windows in NGV facilities should be closed except when they are being accessed. For example, standard practice in many facilities is to prop the restroom door open, so vehicle technicians have easier access from the vehicle service area. Doors cannot be propped open in NGV maintenance facilities. Instead, doors should have automatic closers installed so that they remain closed when not in use.
Similarly, some facilities have sliding or other windows that open from an office or parts storage room into the vehicle service area. In NGV maintenance facilities, these windows should not be left open or used for ventilation. For the most part, windows into the vehicle service area should be inoperable. If there are operable windows, for instance between the parts room and the service area, they should have automatic closers installed so that they remain closed until required to be opened, and close when not in direct use.
These examples assume that the wall extends from the floor to the ceiling. But sometimes facilities are designed with a partial wall that does not reach the ceiling. They can be used to separate bays within the VMF, or separate the vehicle service area from other parts of the facility. Any part of the facility that allows gas to reach from the vehicle service area is subject to the same codes and standards as the rest of the VMF.
For instance, if gas is allowed to escape over a partial wall into an adjacent room, such as a tire room, the tire room must meet all of the same codes and standards as the vehicle service area. Obviously this is not an ideal situation because you do not want to modify more space than necessary because it will significantly increase the cost. In this case, it may be more economical to extend the partial wall to the ceiling rather than modify the tire room to the same standards as the vehicle service area.
Construction methods at the ceiling level of the facility should allow natural gas to dissipate freely across the ceiling. In the unlikely event of a natural gas leak, open purlin roof or open truss roof support structures will help facilitate the dispersal of natural gas. However, in some cases large
I-beam corner joints can create enough of an enclosed area for escaping natural gas to collect and become a hazard, especially if it is positioned directly over an area where a potential leaking vehicle could be parked. This type of ceiling construction may require installation of a ducted air supply system that will sweep the enclosed area.
Also, if the roof is pitched, escaping gas can collect at the high point of the ceiling. There must be a way for the escaping gas to disperse and be exhausted outside the facility.
These are only a few of the more common scenarios encountered when evaluating the building envelope during a VMF—there are perhaps dozens of others because again, each facility is unique. Ultimately the goal of every VMF is to identify modifications that will ensure the safety of your employees, customers and the general public.
Next month we will explore the heating system in a vehicle maintenance facility and how it is impacted by NGVs.