Heathus OMD, Manual

Page: 52 / 60

52
In most paved locations the survey can be conducted by
driving 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 may be traversed in both directions. In un-
paved locations, sampling is done as close to the buried
structure as possible.
When the detector senses the presence of methane in the
light path, an audible alarm sounds and a read-out of the
amount of methane detected is indicated on the display.
The consultant will stop the unit and make plunger bar
holes to confirm, with a combustible gas indicator, the
presence of a combustible in the soil and then center and
classify the leakage indication. Results are then recorded
and the survey is resumed.
The client should supply accurate maps to the consultant.
These will be used to determine which streets to survey
and where the mains are located.
As each successive street is surveyed, coverage is recorded
on the map and color coded as a record of the daily street
coverage.
D. Survey Procedures (Patrol Type Survey)
The patrol type survey is conducted in the same manner
as the standard survey, with the exception that the speed
a vehicle travels can be much higher. Once an indication
is detected, the same confirmation, classification and re-
port procedures, as in the standard survey, are used.
The use of a patrol survey, during severe conditions such
as heavy frost, is a means of detecting large volume leaks
that are venting to the atmosphere. The survey should
not be considered a thorough survey, but only as a supple-
ment to the standard survey program.
S
URVEY