OSHA Confined Space Ventilation Requirements | Chart | Types | Calculation

OSHA Confined Space Ventilation Requirements | Chart | Types | Calculation

1. Blowers and/or fans may be used, if needed, to provide fresh air from a location safe from contamination. The need for ventilation must be evaluated as part of the entry planning.
2. Ventilation can be used as a precautionary measure to prevent the accumulation of hazardous atmospheres, for the comfort of the Entrants or to control the atmosphere within acceptable limits. When ventilation is used to control an atmospheric hazard and maintain the atmosphere within acceptable limits, continuous monitoring must be used.
3. If mechanical ventilation is used, the space should have at least two openings. Mechanical ventilation equipment must not block access routes.
4. Venturi type air movers must be positioned to pull air from the confined space, unless supplied by a certified breathing air source.
5. Ventilate the permit-required space to obtain and maintain acceptable entry conditions with the following exception: Where work within the permit required confined space will be carried out in an inert atmosphere and appropriate procedures have been provided to work in this IDLH atmosphere.
6. Power and supply sources to ventilation and purging equipment must be locked and tagged as part of the Lockout/Tagout strategy in order to prevent inadvertent shut-down of this equipment. New Safety Work Permits must be reviewed to ensure they don’t affect this equipment. Consideration of loss of ventilation due to external (to the facility) power failures must be accounted for in the entry planning as a potential hazard.

7. Burning/Welding in Confined Spaces

   • The space must have adequate ventilation if burning or welding is to take place. In addition, the following precautions should be taken:
     • In addition to general ventilation, local fume extraction equipment should be used to remove toxic gases, smoke, welding gases, and fumes at the source. These contaminants should be vented at a suitable place, well away from confined working areas (or their ventilation sources). In the event of ventilation or extraction failure, all burning or welding should stop immediately.
     • Oxy-acetylene torches should be removed but, as a minimum, have the cylinders shut off and the regulators backed off when not in use.
     • If electric arc welding is to take place in a vessel, then the welding machine must be securely grounded (earthed) per equipment manufacturer’s recommendation.
     • If tungsten inert gas (TIG) welding is to take place in a vessel, then the shielding gas to the torch and the back purge for the weld metal, must be turned off when not required. This will prevent a build up of inert gas in the area.
     • Constant atmosphere monitoring must be conducted for O2 and LEL. Consideration should also be given to constant monitoring for CO, CO2 and other toxics based on the ventilation provided.
     • Follow the precautions outlined in 25-010519.

8. Cryogenic Equipment Enclosures

   • Cryogenic equipment enclosures (boxes and cans) filled with insulation should be ventilated with low volume suction to eliminate the disturbance of the insulation caused by high volume fans.
     • Placement of the suction side of the equipment should be located near the work area.
     • The discharge is extended beyond the opening to prevent recirculation of the can or box atmosphere.
     • Small blowers or fans can be used to supplement the fresh air feed from the outside.
   • Connected cold boxes or cans may allow nitrogen or other gases to migrate into the work area through crossover ducts. To prevent this from happening:
     • Process piping and box purges in connected cold boxes must be isolated/disconnected.
     • Ducts must be opened and ventilated if leakage is possible from process piping.
9. Under no circumstances should oxygen be introduced into a confined space to remove gases or vapors or to freshen the air. Dangerous situations can result from oxygen enrichment in atmospheres and serious accidents, some fatal, have been caused by the misuse of oxygen in this manner.
10. When deciding upon mechanical ventilation methods, the danger of static electricity causing fire or explosion should be given consideration. These circumstances could arise in the event of an inadequate or interrupted ventilation allowing a flammable atmosphere to develop while work is in progress. If such circumstances could occur, special precautions such as earthing and bonding of trunking and/or air lines to the metalwork of the confined space should be taken.