Operators of underground mines should be aware of the capacity of PVC cement to release vapors that can be falsely read as elevated levels of methane and CO.

The Mine Safety and Health Administration (MSHA) notes that its April 2008 rule on sealing abandoned mines prohibited metallic sampling pipes in seals constructed after October 20, 2008. PVC pipes therefore became the option of choice to meet the sampling pipe requirement. The most common method for connecting pipe segments, fittings, and valves is to weld the components using PVC cement.

MSHA reports that miners were recently evacuated from a mine after handheld atmosphere detectors in the sealed area indicated methane and CO levels exceeding acceptable limits. Bottle samples subsequently indicated no measurable methane or CO levels. MSHA investigators found that vapors from the PVC cement used to weld the PVC pipes valves affected the response of the gas sensors.

To avoid false or elevated readings of methane and CO caused by PVC cement vapors, MSHA recommends that sample pipe and valve installations be completed as soon as possible at seal sites to allow the cement to become fully cured. After complete curing, the cement will no longer produce vapors in sufficient quantity to affect the readings of the handheld detectors. In addition, examiners should ensure that the sample pipe is properly purged after the curing process is completed to remove any vapors remaining in the sample pipe.

[Source: Environmental Manager's Compliance Advisor. Subscribe today!]