Heath Consultants Optical Methane Detector (OM) - Manual (Page 43)

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the consultant should make every effort to place the OMD
over available openings. When the detector senses the
presence of methane in the sample, an audible alarm
sounds and a read-out of the amount of methane detected
is indicated on the display. If necessary the consultant
can stop and rerun the suspected area to better establish
the point(s) of venting. Then plunger bar holes are made
to confirm with a combustible gas indicator, the pres-
ence of methane in the soil. The leak indication is then
centered and classified. The results are recorded and
the survey is resumed.
In paved locations, the survey can be conducted by sam-
pling along the curb, or the side of the street, where the
main is located. However, in the instance of dual mains,
particularly wide streets or divided traffic lanes, a par-
ticular street should be traversed in both directions. In
unpaved locations, sampling is done as close to the bur-
ied structure as possible.
The consultant will use system maps to determine which
streets to survey and where the main is in the street. As
each successive street is surveyed, it is recorded on the
map and color-coded as a record of the daily survey cov-
erage.
D. Survey Coverage
A standard mobile survey includes designated gas mains.
It does not include service line inspections. Mains or
service lines that are not accessible to the mobile unit,
may be inspected as described in the portable flame ion-
ization survey procedures. Example: in areas where ve-
hicles are parked over the main, the consultant would
consider using the flame ionization instrument in the
portable mode. Often, it is advisable to survey both sides
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