When a worker must enter a confined space with potential hazards, a confined space work permit is required. There are two categories of hazards associated with permit-required confined spaces, physical and atmospheric.
Physical hazards pose direct, immediate danger to the inside or outside of the worker’s body. Common physical hazards include falls, materials falling into the space, configuration of the space, electrocution, engulfment, and stored materials.
Atmospheric hazards affect air quality and present immediate health hazards. Acceptable atmospheric conditions must be verified before entry, and must be monitored continuously while the space is occupied. The three conditions that must be monitored are oxygen concentration, flammable or combustible material, and the presence of toxic gases.
Safe oxygen concentration is between 19.5% and 23.5% of the total atmosphere, and entry is not allowed until the concentration of a confined space is within these levels. Oxygen deficiency occurs when the oxygen level is less that 19.5%. Exceeding 23.5% oxygen is also dangerous because it increases risk of fire.
Atmospheres must be tested for the presence of flammable or combustible materials. The lowest concentration of a material that will sustain a flame is known as the Lower Explosive Limit, or LEL. Work cannot begin, or must be stopped, if the concentration of a material reaches or exceeds 10% of the LEL.
To protect workers against exposure to airborne hazards, contaminants have permissible exposure limits, or PELs. The PEL is the mandatory limit on the amount or concentration of a particular material in the air, and is measured in parts per million, PPM. Some gases that are commonly monitored in the offshore and maritime industries are hydrogen sulfide and carbon monoxide.