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4. In the case of flammable gases such as methane, a dangerous air contamination due to flammability of a gas or vapor is defined, (in California, Title 8, Article 108, Confined Spaces, Section 5156,) as any concentration greater than 20 percent of the lower explosive limit (LEL) for any substance. There is no equivalent Federal OSHA standard, so check local and state codes. ' An atmosphere considered to be an immediately dangerous to life and health (IDLH) atmosphere is one containing less than 19.5 percent oxygen by volume or one containing a concentration of another hazardous or toxic chemical at or above the limits set by NIOSH_ 5. Note that while the Resource Conservation and Recovery Act (RCRA) (40 CFR, Part 257.3-8 Safety) places limits on the maximum allowable methane concentration in landfill facility structures, on or near.landfills, at not to exceed 25 percent of the LEL or 1.25_percent methane gas in air (by.volume), local OSHA regulations on flammable or combustible environments may place a more stringent requirement on the maximum concentration allowed in a working enviroriment (i.e., an occupied structure which is not private and residential). • 6. The flammable range for methane is approximately 5 to 15 percent in air at sea level at 25 Degrees C. As little as 0.3 millijoule of static electricity is sufficient to cause a methane ignition. This has been equated to 1/50 the amount of static electricity accumulated by a person walking across a carpeted floor on a dry day. The autoignition temperature of methane is 1004 Degrees F. The specific (vapor) density of methane is 0-6 that of air while the specific density of undiluted LFG is normally about 1 .0 (close to that of air, depending on constituent concentrations). Therefore it should not be automatically assumed that because LFG contains methane the mixture is lighter than air and will rise. • Behavior of LFG will vary with its constituent makeup which also varies. 7. Prior to the entry of workers into an excavation, vault, or ditch deeper than 3 0 feet, and routinely during construction, the atmosphere in the excavation should be tested for explosive concentrations, oxygen deficiency and H7S levels. Air blowers or fans should be available for positive ventilation. A pressure-demand SCBA or supplied air respirator must be used when entering areas containing hazardous and/or oxygen-deficient atmospheres. APRs with chemical cartridges can be used for gaseous contaminants (but not HZS) if all 0 of the following conditions are met: if the oxygen concentration is satisfactory, if the chemical contaminants have been identified, the concentrations have been monitored, the cartridges are effective in removing the contaminants, and all the contaminants have good warning properties. Mechanical filter respirators should be used only for protection against appropriate particulate mater for which they are rated_ • 0 1: 14 • • • 0