“Purging” involves removing contaminants inside the confined space by displacement with air to achieve acceptable atmospheric levels. For example, if a confined space originally contained a toxic gas, air would be blown into the space to reduce the concentration of the toxic gas to below the appropriate atmospheric exposure level. After the contaminants have been removed (“purged”), the confined space may be ventilated. “Ventilation” means the continuous provision of fresh air into the confined space by mechanical means to maintain acceptable atmospheric levels. It must be continued while work is being carried out within the space, to maintain an acceptable oxygen concentration, to provide protection in case of accidental release of chemicals, to remove contaminants generated by the work performed, or to cool the enclosure. Ventilation involves displacing air and diluting it through the introduction of fresh air (forced-air) or the continuous removal of contaminants by local exhaust ve