Due to poor ventilation and physical structure, the atmosphere in confined spaces may be actually or potentially hazardous. Certain chemical or biological reactions may reduce oxygen over time, but employee operations such as cutting or welding may reduce oxygen content very quickly. Oxygen levels must be tested regularly whenever hotwork is performed within a confined space. Combustible atmospheres have enough oxygen and flammable vapor, gas, or dust to ignite and support a fire or explosion if exposed to flames, sparks, or heat. Oxygen-enriched atmospheres and hazardous atmospheres in excess of their lower flammable limits are extremely combustible and dangerous.
Toxic atmospheres can cause injury, illness, or death.
Safety concerns include inhalation and skin exposure. Ventilation controls the atmospheric hazards of a confined space by replacing unsafe air with clean, breathable air. There are several methods for ventilating a confined space. Two common types of mechanical ventilation include local exhaust ventilation and general ventilation. Local exhaust ventilation captures contaminants at their point of origin and removes them.