Ventilation | Permit-Required Confined Spaces
Ventilation is the process of continuously moving fresh, uncontaminated air through a confined space. Ventilation dilutes and displaces air contaminants, assures than an adequate supply of oxygen is maintained during entry, and exhausts contaminants formed by processes such as welding, oxy-fuel gas cutting, or abrasive blasting. Oxygen levels must be maintained within a range of 19.5 to 23.5 percent.
Ventilation by a blower or fan may be necessary to remove harmful gases and vapors from a confined space. There are several ventilating methods and equipment to choose, depending on the size of the confined space openings, gases to be exhausted, and source of makeup air.
Equipment selection considerations include the:
§ Physical structure of the space,
§ Space’s previous contents,
§ Existence of natural drafts,
§ Number and location of any openings, and
§ Nature of any contaminant-producing tasks that may be performed in the space.
Because ventilating may create the potential for static electricity, always follow appropriate bonding and grounding procedures.
Under certain conditions where flammable gases or vapors have displaced the oxygen level, but are too rich to burn, forced air ventilation may dilute them until they are within the explosive range. Typically, an opening is made in the top or side of the space and clean air s blown into it. Dilution works best with low toxicity and concentration levels and when the contaminants are well distributed.
Ventilation should be continuous where possible, because in many confined spaces, the hazardous atmosphere will form again when the flow of air is stopped. Be sure that the source of air intake is not placed where it can draw carbon monoxide (as from an idling vehicle parked close by) or other contaminants into the space.
A common method of ventilation requires a large hose, one end attached to a fan and the other lowered into a manhole or opening. For example, a manhole would have the ventilating hose run to the bottom to blow out all harmful gases and vapors. The air intake should be placed in an area that will draw in fresh air only.
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