TR design rules; Toxic gas refuge shelter design rules; temporary refuge shelter

TR which has been designed to protect against toxic gas include the following:

• Positively pressurized (minimum of 50Pa)
• Airtight
• Fresh air is stored air cylinder to ensure availability of air for the duration of TR considering maximum TR POB, potential leaks sources, door opening, etc
• Entrances with double sets of doors (airlock facility with air curtain to purge toxic gas trapped with personnel entering the airlock) and located as far as possible away from sources of H2S, interlock shall be in place to prevent both airlock doors being opened simultaneously or to alarm to warn of this condition. The location on the doors to buildings should be such that entry to the building is from side which is not directly facing to facilities to reduce the potential toxic gas ingress while in use.
• Doors shall be closed all the time except when in use. Or be automatic closing, for example by magnetic hold open, released on gas detection. Attention should be paid to avoid hazards with automatically closing doors such as trapped fingers, e.g. doors should be slow closing.
• HVAC shall be automatically shut off on detection of toxic gas at the air intakes, and dampers in the air intakes and exhaust shall close to shut in the building. Reliability of detection shall be determined as part of the design, and shall comply with the requirement for the protection.
• Toxic gas detectors shall be provided at HVAC inlet as well as within the airlock. Alarm provision shall be provided accordingly.
• A mechanism to allow manual initiation of HVAC shutdown from within the TR.
• TR leak tightness test shall be carried out to ensure the gas tightness and to confirm the air exchange rate considered in design of TR. 

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