scope:

INTRODUCTION

General. This standard has been developed to identify performance requirements for pressure relief devices for Natural Gas Vehicle (NGV) fuel containers. This standard sets minimum requirements for pressure relief devices produced for use on NGV fuel containers. NGV fuel containers comply with ANSI/IAS NGV2, Basic Requirements for Compressed Natural Gas Vehicle (NGV) Fuel Containers [4], FMVSS 304, Federal Motor Vehicle Safety Standards, 49 CFR Part 571.304, Compressed Natural Gas Fuel Container Integrity [2], and/or CSA B51, Part 2, High Pressure Cylinders for On-Board Storage of Natural Gas as a Fuel for Automotive Vehicles [5], as appropriate. These fuel containers are intended only for the on-board storage of high pressure compressed natural gas as a fuel for automotive vehicles to which the containers are permanently attached. Regulations and standards which apply to fuel container installation and vehicle systems include FMVSS 303, Federal Motor Vehicle Safety Standards, 49 CFR Part 571.303, Fuel System Integrity of Compressed Natural Gas Vehicles [1], CS 301.2, Transport Canada/TC, Motor Vehicle Safety Regulations, Schedule IV, CNG Fuel System Integrity [3], NFPA 52, Compressed Natural Gas (CNG) Vehicular Fuel Systems [6], and B149.4, Natural Gas for Vehicles Installation Code [7].

Application. Natural Gas Vehicles use fuel containers categorized as follows:

Type 1 (NGV2-1 or CNG-1) Metal

Type 2 (NGV2-2 or CNG-2) Resin impregnated continuous filament with metal liner of prescribed strength;

Type 3 (NGV2-3 or CNG-3) Resin impregnated continuous filament with metal liner;

Type 4 (NGV2-4 or CNG-4) Resin impregnated continuous filament with a non-metallic liner "full wrapped".

These fuel containers may accidentally be exposed to fire or elevated temperature. These conditions may act to increase the contained pressure and/or to degrade the structural materials, depending on the container type and materials of construction. A pressure relief device (PRD) will provide a means to vent the fuel container under these conditions.

Specific pressure relief devices may not be suitable for all container types and sizes. The container and pressure relief device system must be tested as prescribed in the fuel container standards to insure compatibility.

WARNING [18]: Pressure relief devices may not prevent rupture of a container under all conditions of fire exposure. When the heat transferred to the container is localized, intensive, and remote to the relief device, or where the fire builds extremely rapidly, such as in an explosion, and is of very high intensity, the container may weaken sufficiently to rupture before the relief device operates, or while it is operating.