covering as much area as possible, especially near the
Use cotton waste for cleaning purposes; other
bottom and around baffles. Remove air lines and drain
solution from tank at all valves and drain points.
(7) Fill tank with cold water and allow to
(1) Adequate source of water with a large
overflow for 5 minutes or until water is clear. Drain tank
diameter hose long enough to reach the semitrailer.
completely at all valves and drain points.
(2) Compressed air source and air hoses of
(8) Conduct a combustible vapor test to
determine if tank is safe to repair, clean, paint, store,
sufficient length to reach bottom of semitrailer tank.
change material, or ship. Take reading in several areas of
(3) Sufficient quantity of gas tank purger
the tank. If test reading indicates tank is not safe, repeat
chemical obtainable through local procurement. Purging
step (7), until a safe reading is obtained.
chemical No 913, Product-Sol Inc., 2010 Cole Avenue,
Birmingham, Michigan 48008 is the only known source
available to date. Purging chemical can be procured at a
(1) This methods is an alternate to the chemical
cost of approximately .00 per 5 gallons, or 0.00 per
method, It is effective for the removal of high viscosity
55 gallons, plus shipping cost.
petroleum products. Low pressure steam is injected into
the tank for a period of time to bring the temperature of
(4) Combustible gas indicator set (NSN 6665-00-
the tank to 76C (170F). Prior to introducing steam, the
metallic connection on the discharge end of the steam
listed as a Common Table of Allowance (CTA) item in SB
hose must be bonded to the tank shell and the tank must
700-20 and is line item number E57351.
(5) Entry into a tank which is not vapor-free or
(2) After draining tank, ensure that all valves and
which has an oxygen content less than 19.5% require the
drain points remain open.
following: Protective respiratory equipment; lifeline;
approved explosion-proof extension light or flashlight;
(3) Introduce steam through manhole and baffle
steam or air-operated venturi-type air mover or a fan-type
plate opening in sufficient volume to raise the
blower with an air duct.
temperature of the tank to 76C (170F). Close manhole
fill cover to the extent steam line will permit.
(1) After draining tank, close or seal all valves
and drain points.
Ensure that steam does not come in contact
(2) Fill tank with cold water and allow to
with electrical wiring and other components.
overflow for five minutes or until all traces of flammable
The heat of steam can damage the painted
material are removed. Drain tank completely.
surface of the tar, valve seats, gaskets, and
diaphragms, and can weaken fusible plugs.
(3) Close or seal all valves and drain points.
(4) Steam the tank for at least three hours. Turn
steam source off.
Insufficient amount of chemical will result In
an incomplete purging. Once purging has
begun, do not stop until process Is complete.
After purging by steam method, leave tank
valves and drain points open during
(4) Add to tank 40-fluid ounces of the
cool-down to prevent vacuum collapse of
chloro-carbon base purging chemical for each 100-gallon
capacity. A 5000 gallon tank will take approximately
17 gallons of purging chemical.
(5) Leave an valves and drain points open until
(5) Fill tank to top with water. Do not overflow.
tank is fully cooled, at least one hour.
(6) Measure explosive vapor level. Take readings
(6) Insert air line through manhole and vent cap
in several areas of the tank. Reading should be 20% lower
openings and agitate solution with 3-5 psi of air for
explosive level (LEL) or less. If LEL is greater than 20%,
40 minutes. Frequently move air hoses around in tank,