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U.S. Department of
Labor |
Mine Safety and Health Administration 4015 Wilson Boulevard Arlington, Virginia 22203-1984 |
ISSUE DATE: September 30, 1997 PROGRAM INFORMATION BULLETIN NO. P97-24 FROM: KENNETH T. HOWARD
SUBJECT: Portable Methane Detectors Magnetically Attached to
Purpose
Information
A survey conducted by CMS&H showed that three types of detectors comprised 89 percent of the units used with magnets: the CSE Models 102 and 102-LD, and the Industrial Scientific Model CD210. Also being used are the Industrial Scientific Models MX250 and CMX270. Samples of these were not available for testing from the manufacturer because they are no longer produced. Likewise, samples could not be readily supplied by the districts. The survey shows that only 4 percent of the mines are using either of these types of detectors. Because of their similarity to detectors that were tested, the Industrial Scientific Models MX250 and CMX270 should not be affected by magnets. MSHA has made no determination as to other detectors in use. Their performance may or may not be affected by the presence of the magnets.
Background The method uses either a commercial or a custom detector bracket mounted to a magnet either directly or by means of a post. The post is made of steel or flexible conduit and varies in length from 2 to 36 inches. The "pull" rating of the magnets ranges from 90 to 250 pounds. Each MSHA District Office investigated the equipment comprising each "gizmo" used underground and provided the information to the Approval and Certification Center (A&CC). The A&CC then obtained representative samples of the magnets, brackets, and detectors. The magnets obtained and tested did not include every magnet type reported to be in use. Rather, the magnet/bracket/detector configurations that presented the greatest likelihood of magnetic interference were determined and tested, without testing every configuration. For initial testing, MSHA mixed test gas per 30 CFR 22.7(d); monitored the concentration of the test gas; introduced the test gas to the detector via the appropriate calibration adapter; and monitored the reading on the methane detector while it was mounted in the "gizmo" which was placed on a laboratory bench. A magnet's greatest effect on a methane detector would most likely occur with an alternating magnetic field, which would require the magnet to rotate in relation to the detector. The magnet used with the "gizmo" in the field will remain substantially stationary in relation to the detector. To simulate the magnetic field moving in relation to the detector, vibration tests were performed. The "gizmo" was magnetically attached to a vibration table that was operated per 30 CFR 27.39(a). The accuracy of the detectors was then tested in the same manner as before. A complete report of testing is available from the A&CC, Division of Electrical Safety.
Authority
Issuing Office and Contact Person
Coal Mine Safety and Health, Safety Division
Distribution |
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