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1.9 VENTILATION PROCEDURE
Enabling Objective: State the proper forced air ventilation procedure.
In a previous section, you learned that a power ventilator blower is used to force air into a structure. In this section, you will learn how to use the power ventilator blower. The following steps are to be followed when using this tool. GEHSI S17.02.02, Ventilation of Underground Structures, provides guidance on how to properly ventilate underground structures.
•The power ventilator shall be kept at a safe distance and secured from the enclosure opening to prevent air recirculation.
• Ensure that the blower hose is not unnecessarily bent.
• Purge the blower hose outside of the enclosure for at least one minute to prevent the possibility of introducing contaminants into the enclosure.
• If a tent will be used over the enclosure opening, the power ventilator must be kept outside of the tent and the tent sides must be one foot off the ground for air circulation.
• Purge the confined space for at least 10 minutes, or, if a tent is used, purge for at least 15 minutes.
• After the required purge time has elapsed, sample the atmosphere of the enclosed space. If the results are unsatisfactory, continue the air purge for an additional 10 minutes.
• Once the gas analysis has passed, personnel may enter the enclosure to take additional air samples. Test areas include corners, duct edges, cracked ar- eas, top of sumps, etc.
• Move the blower hose onto a cable rack so that its output is on a horizontal plane. This is the ventilate mode.
•Perform atmospheric test at least every 2 hours when using powered ventilation.
• If water is present in the vault or manhole, it must be pumped out and another air sample must be taken. Air samples must be taken immediately after
a sealed duct is opened.
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