Working Principle (Cont’d)
4. FOG IGNITION. The greatest hazard of fog ignition is from an external source.
This can be gas or oil pilot lights or sparks from electrical controls such as
switches, relays, etc. Therefore, it is strongly recommended that all such sources
be eliminated by extinguishing all pilot lights and turning off all electrical power
before fogging.
The design of the machine is such that it is quite difficult to ignite the fog from an
external source since the ignition must be positioned just at the proper distance
from the discharge end to cause fog ignition and this distance is on the order of
only 6-8 inches (-FP). If an external source ignites the fog being
discharged, it will produce a torching effect. Should this occur, quickly release the
FORMULATION ON-OFF LEVER to stop the fog discharge. Never artificially
wedge, or block open the formulation ON-OFF VALVE.
On a DRY FOG setting, which must always be employed indoors and in confined
areas, the ignition source must be continuous since the fog will not continue
torching except briefly if the ignition source is removed. On a WET FOG setting,
it is possible for the fog to continue to torch after removal from the ignition source.
Never use a wet fog setting indoors and in confined spaces. Extreme caution
must be exercised when using a wet fog setting under all circumstances. A wet
fog setting can leave a deposit of liquid on combustible surfaces creating a fire
hazard should torching take place.
A second source of fog ignition can be the machine itself. If the machine stops
running for any reason including running out of gasoline, the operator must
quickly release the FORMULATION ON-OFF LEVER to stop the fog discharge.
If the engine stops, it is possible for some formulation to flow into the still hot
engine tube where it will vaporize. Part of this vapor may then be drawn by
natural thermal convection back through the annular cooling air space between
the cooling duct and the engine tube, to the red hot engine combustion chamber.
If the proportion of vapor to air is just right when this occurs, the vapor will ignite
