1-1.1 This recommended practice provides appropriate methods for responding to fire and explosion hazards resulting from the release of a flammable or combustible liquid, gas, or vapor that could migrate to a subsurface structure. Although this recommended practice is intended to address only these fire and explosion hazards, other authorities should be consulted regarding the environmental and health impact and other hazardous conditions of such releases. 1-1.2 This recommended practice outlines options for detecting and investigating the source of a release, for mitigating the fire and explosion hazards resulting from the release, and for tracing the released liquid back to its source. These options are not intended to be, nor should they be considered to be, all-inclusive or mandatory in any given situation. If better or more appropriate alternative methods are available, they should be used. 1-1.3 The procedures outlined in this recommended practice can apply to hazardous substances other than flammable and combustible liquids that could have adverse human health effects. However, the physical characteristics of the hazardous substance released must be understood before taking any action. It should be recognized that other authorities, such as federal or state hazardous materials personnel, should be consulted regarding the environmental and health impact and other hazardous conditions of these substances. Guidance regarding maximum acceptable levels of these substances can be found in the Material Safety Data Sheet (MSDS); OSHA 29 CFR 1910.1000, Subpart Z; other OSHA substance-specific standards; ACGIH Threshold Limit Values (TLV) for Chemical Substances and, Physical Agents; and the NIOSH Pocket Guide to Chemical Hazards. 1-1.4* The condition created by the releases of liquids and vapors in subsurface structures can be grouped into the following two classes: (1) Flammable (2) Injurious to life The latter condition results from the toxic or suffocating properties of the gases or vapors. Some of these liquids and gases fall into both classes. While this publication deals primarily with the flammable limits associated with liquids and gases, some of which are listed in Table A-1-1.4, additional precautions could be required to protect against health hazards. An example is benzene; its dangerous breathing concentration is only a small fraction of the lower flammable limit (LFL). 1-1.5 The responsibility for proper handling of a suspected release of flammable and combustible liquids and gases, or a potential hazard from such a release, will be shared by various individuals, organizations, and regulatory agencies. The successful handling of these problems will depend on the best possible cooperation between them. This recommended practice is intended for the information of all organizations and persons involved. Owners, operators, or others becoming aware of a hazardous condition should notify the fire department, police, or other proper authority. 1-1.6 The National Fire Protection Association does not, by the publication of this recommended practice, recommend action that is not in compliance with applicable laws and regulations and should not be considered as doing so. Users of this recommended practice should consult all applicable federal, state, and local laws and regulations, especially with respect to any applicable reporting requirements.