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® 8. Fires and explosions in confined spaces require a source of ignition. Smoking <br /> ® is strictly forbidden except in well-ventilated areas. Nonsparking and/or <br /> ® explosion-proof tools should be used in vaults, trenches, and other enclosed <br /> ® areas. Positive ventilation is required in construction shacks or other structures <br /> ® on or near a landfill. Temporary structures on the landfill surface should be <br /> constructed on blocks or other supports, with a ventilated area under the main <br /> ® floor. Construction equipment should be equipped with a vertical exhaust at <br /> ® least 5 feet above grade and/or with spark arrestors. <br /> ®® 9. H2S gas is usually always present at some concentration, generally below 100 <br /> ppm, in LFG. It is unlikely that hazardous concentrations of H2S will build up <br /> ® (see Table -1) except in vaults or other confined spaces .where oxygen <br /> deficiency may be a hazard. However, in special circumstances; where there <br /> is an natural or manmade presence of gypsum along with high.moisture,: for <br /> example, very high (lethal) concentration levels of H2S may be produced at <br /> ® landfills. A large amount of construction debris containing wallboard <br /> concentrated in one location at a landfill would be another potential example. <br /> Thus, dangerous and unexpected pockets of H2S gas could be encountered <br /> ® under certain circumstances. Personnel must be trained for, and alert to, these <br /> possibilities. <br /> ® One must always remain alert to observe such conditions. Air-purifying <br /> respirators are not normally effective against H2S unless specifically rated for <br /> such use, and then only for a limited concentration and duration of use. In <br /> situations when high concentrations of H2S are known or suspected pressure- <br /> demand SCBA or supplied air respirators should be used. <br /> 10. Employees with beards should not work in areas where snugly fitted air masks <br /> or respirators may be necessary. All employees should be fit-tested on the <br /> ® respirator that they will wear in order to assure a proper facepiece seal against <br /> the face. Fit-testing should reoccur at least annually. <br /> ® 1 1 . For employees who wear glasses, respirator eyeglass inserts should be provided <br /> if full-face masks are used. The wearing of contact lenses with any type of <br /> ® respirator shall be prohibited. <br /> 1: 15 <br />