drums, tanks, or other containers is extremely dangerous
and could lead to property damage or loss of life.
Whenever available, use steam to remove materials
that are easily volatile. Washing the containers with a
strong solution of caustic soda or a similar chemical will
remove heavier oils.
Even after thorough cleansing, the container should
be further safeguarded by falling it with water before any
cutting, welding, or other hot work is done. In almost
every situation, it is possible to position the container so
it can be kept filled with water while cutting or other hot
work is being done. Always ensure there is a vent or
opening in the container for the release of the heated
vapor inside the container. This can be done by opening
the bung, handhole, or other fitting that is above water
When it is practical to fill the container with water,
you also should use carbon dioxide or nitrogen in the
vessel for added protection. From time to time, examine
the gas content of the container to ensure the concentra-
tion of carbon dioxide or nitrogen is high enough to
prevent a flammable or explosive mixture. The air-gas
mixture inside any container can be tested with a suit-
able gas detector.
The carbon dioxide concentration should beat least
50 percent of the air space inside the container, and 80
percent or more when the presence of hydrogen or
carbon monoxide is detected. When using nitrogen, you
must ensure the concentration is at least 10 percent
higher than that specified for carbon dioxide.
Carbon dioxide or nitrogen is used in apparently
clean containers because there may still be traces of oil
or grease under the seams, even though the vessel was
cleaned and flushed with a caustic soda solution. The
heat from the cutting or welding operation could cause
the trapped oil or grease to release flammable vapors
that form an explosive mixture inside the container.
A metal part that is suspiciously light maybe hollow
inside; therefore, you should vent the part by drilling a
hole in it before heating. Remember: air or any other gas
that is confined inside a hollow part will expand when
heated. The internal pressure created may be enough to
cause the part to burst. Before you do any hot work, take
every possible precaution to vent the air confined in
jacketed vessels, tanks, or containers.
JUDGING CUTTING QUALITY
To know how good of a cutting job you are doing,
you must understand know what constitutes a good
Figure 4-31.Effects of correct and incorrect cutting procedures.
oxygas cut. In general, the quality of an oxygas cut is
judged by four characteristics:
The shape and length of the draglines
The smoothness of the sides
The sharpness of the top edges
The amount of slag adhering to the metal
Drag lines are line markings that show on the sur-
face of the cut. Good drag lines are almost straight up
and down, as shown in figure 4-31, view A. Poor drag