Page 45 - Moving the Earth_ The Workbook of Excavation

LAND CLEARING AND CONTROLS

LAND CLEARING AND CONTROLS 1.45

spots where fire might cross. If the brush is heavy, the dozer may turn to push heaps of it out of
the path. An angle dozer or a heavy grader might be able to make a single clean cut in each direction,
turning the sod and brush out from the center.
In grass or light brush, a plow or heavy disc harrow might do a better or faster job than a dozer.
The plow makes a rather narrow strip with each trip, and is subject to jamming with brush but does
not have to go back over its work. A harrow may require several trips and might not be effective.
The hand tools listed earlier may be used to build a complete break, or to work one over after
the machinery has passed.
Backfires. A strong fire adds to the force of the wind which is moving it, somewhat as a blow-
torch builds up its fuel pressure. The combined force may be enough to project a sheet of flame
many feet in front of the burning line, and to shower sparks for long distances ahead. For this reason,
the fire may cross a break of any practical width and make the area too hot for fire fighters.
The principal use of the firebreak is to provide a line from which backfires can be started.
Since the break is made on the downwind side of the fire, a new fire started on that edge burns
upwind. The backfire should be made in a continuous strip along the break so that it will not be
able to turn and blow back toward it. It will increase in strength as it progresses, but will be steadily
farther away from the protected side. When it meets the main fire, there is liable to be a spectacular
flareup and heavy production of sparks. If the backfire has been started in time, this should be far
enough away from the break that few sparks will cross it, and those can be extinguished by men
patrolling the break. If no shift in wind occurs, the sides of the fire can then be put out by the crew
working from behind, aided by the firebreak crew.
If the break is made in a forest where the flames might crown (burn in the tops), the trees on
each side of the break should be bulldozed or cut so as to fall away from the center.
Since a change in wind direction may occur at any time, care should be taken not to start back-
fires prematurely, and to keep workers and machines in positions where they can get away if the fire
turns toward them. The burnt-over area, ponds or wet swamps, and plowed land or well-grazed
pastures are suitable retreats.
Workers on the fire lines must be kept provided with food, water, and tools, and relieved for
rest periods. Machinery must have fuel but may be skimped on other maintenance in sufficiently
dangerous situations.
Backfiring, and possibly other phases of fire fighting, may be regulated or prohibited by local laws.
Rekindling. After the spreading of a fire has been checked, it must be patrolled until all danger
of its making a fresh start has passed. A grass fire in a clean field may be safe to leave within an
hour, while wooded areas containing dead or fallen trees, or rich dry soil, may be dangerous until
after several soaking rains.
Dead stumps may burn a long time and are difficult to extinguish unless ample supplies of water
are available. Fires burning under and between logs on the ground can often be put out by moving
the logs apart, or can be caused to burn out more quickly by piling additional wood on them.
The worst hazards are standing dead or hollow trees, called snags by the lumbermen. If close
to the line, snags may set fire to the unburned area by falling into it. They frequently produce
sparks that may drift long distances. Even thorough soaking may not extinguish them, and it may
be necessary to cut them down or maintain an expensive patrol for days or weeks.
Cutting a burning tree is a tricky and dangerous job, as the cutters are in constant danger of
being hit by falling pieces, and temperatures at the base may be too high for them or their tools.
This job is best left to experienced fire-fighting crews.
Snags may be pushed over by bulldozers, but the tops are apt to fall on the machine. A cab with
maximum-strength overhead protection is needed for operator safety.
The best time to check a burned area for hot spots is immediately after a rain, or a heavy dew,
as the moisture near the fires will steam.

Underground Fires. Underground fires, such as occur in rich forest soils and dried-out swamps,
constitute a special problem. When fire gets in them, often by smoldering down a dead root, they