At what vapor level may workers initially enter a tank for cleaning?

Workers may initially enter a tank for cleaning when the vapor level is below 10 percent of the lower explosive limit (LEL). This standard is established to ensure safety and minimize the risk of explosion or combustion during maintenance activities. The LEL represents the lowest concentration of a combustible substance in air that can ignite and cause an explosion. By keeping the vapor concentration below 10 percent LEL, there is a significant safety margin that helps protect workers from potential hazards associated with flammable vapors. This guideline is critical for operational safety in environments such as fuel and water systems maintenance, where volatile substances are often present.