A competent person performs all air monitoring. The atmosphere must contain at least 19.5 percent and no more than 22 percent oxygen, and oxygen is tested before contaminants. Toxic gases (CO, NO2, H2S and others) and flammable gases are tested as often as necessary.
5 percent of the LEL (methane or other flammable gas): increase ventilation or otherwise control the gas, unless the employer is already operating under the potentially gassy or gassy operation requirements.
10 percent of the LEL near welding, cutting or other hot work: suspend the hot work.
20 percent of the LEL: withdraw all employees (except those needed to eliminate the hazard) to a safe location above ground, and cut power except to acceptable pumping and ventilation equipment.
Hydrogen sulfide: at 5 ppm or more, the affected area is tested at least at the beginning and midpoint of each shift until it has been below 5 ppm for 3 consecutive days. Above 10 ppm, a continuous sampling and indicating monitor is used and employees are informed. The monitor gives a visual and aural alarm at 20 ppm.
Operations are classified potentially gassy if monitoring shows 10 percent or more of the LEL (measured 12 inches from the roof, face, floor or walls) for more than a 24-hour period, or if the history of the area or geological formation indicates that level is likely. They are classified gassy if monitoring shows that level for three consecutive days, if methane or other flammable gas from the strata has ignited, or if the operation is connected to a work area classified as gassy and is subject to a continuous course of air containing the flammable gas. In gassy operations, entrances are posted, smoking is prohibited, and matches and lighters are collected.