Confined space

Confined spaces are dangerous because conditions can change quickly and rescue is difficult. Hazards include oxygen deficiency, toxic gases, flammable vapors, engulfment by loose material such as grain, and hazards from machinery inside. A space may look harmless from the outside, and workers have been overcome within moments of entering.

Some spaces are classed as permit-required confined spaces, where a formal permit system controls entry. Such a system generally includes testing the atmosphere before and during entry, isolating the space from pipes and energy sources, ventilating it, assigning an attendant outside, and having a rescue plan in place. The rules for this are in OSHA standards that you should consult for your industry.

Chemical information from the SDS is part of the planning. Hazards from the stored product, residues, cleaning chemicals or work such as welding and coating must all be considered. Gases heavier than air, such as many solvent vapors, may collect in low areas, and an Asphyxiant can displace oxygen without any warning smell. Atmospheric testing should cover oxygen, flammable gas and relevant toxic gases.

Rescue should never rely on an untrained person entering to help, since many fatalities are would-be rescuers. Trained teams with SCBA or supplied-air equipment, and a plan that matches the space, reduce that risk. Concentrations near the Immediately dangerous to life or health (IDLH) level or lack of oxygen require the highest level of respiratory protection.