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 potential danger exists in these systems whenever high-pressure air is
suddenly admitted into pockets,or dead ends, that are at or near atmospheric
pressure. The air temperature in the confined space is raised to the ignition
point of any flammable material that may be present. This autoignition or
diesel action has been identified as the cause of several major disasters
associated with high-pressure air systems. Such an explosion may set up shock
waves that can travel throughout the compressed air system and possibly cause
explosions at remote points. Under these conditions, even a small quantity of
oil residue, a smear of grease, or a small cotton thread may be sufficient to
cause an explosion. Because of the serious nature of these problems, it is
extremely important that competent personnel,experienced in high-pressure
systems, be employed for maintaining and operating such equipment.
2.2 Preventive Measures. As a safeguard against explosions in high-pressure
compressed air systems, a number of precautions should be taken.
(a) Use of Slow-Opening Valves. These valves are used in pocketed
spaces such as lines to gauges and regulators to prevent a sudden pressure
rise.
(b) Elimination of Flame Arrestors. Flame arrestors, sometimes used to
prevent the spread of flame in pipelines, SHOULD NOT be installed in
high-pressure air systems as they may create additional hazards.
(c) Pipe Coloring. High-pressure air lines
are identified with a
painted light gray band and adjoining light green
arrowhead pointing in the
normal flow direction. These markings are placed
on high-pressure air lines
at each point where piping enters or emerges from
a wall and immediately
adjacent to all valves, regulators, check valves,
strainers, and other
components.
(d) Location of Equipment. High-pressure air storage and dryer
cylinders are isolated from other facilities as a precaution against damage
that could result from rupture of the cylinders.
(e) System Tests. Before putting a high-pressure system into operation,
the required testing of NAVFAC DM-3.5, Compressed Air and Vacuum Systems, must
be accomplished by competent personnel with an engineer responsible for safety.
3 STARTUP.
3.1 Prestart Inspection. Carefully inspect the compressor installation to
ensure the following prestart requirements are fulfilled.
(a) Verify all installation and repair work has been completed.
(b) Ensure system has been cleaned and tested for leaks.
(c) Ensure interstage and discharge safety valves are operating properly.
(d) Ensure compressor and drive are lubricated in accordance with the
manufacturers' instructions.
On units fitted with a forced mechanical
lubricator, pump or crank by hand to see that the oil is getting to all parts
requiring lubrication.
2-3
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