Page 394 - Reciprocating Compressors Operation Maintenance

Safety in Operation and Maintenance 379

WHAT WE KNOW

The few fires we know of and have investigated were caused by the
following:

1. Dirty, scaled-up cylinder water jackets.
2. Oil collecting in low points in discharge piping.
3. Overheating due to compressor valve failure.
4. Overheating due to cooling water failure.

However, it is not possible to attribute a definite cause to all fire events.

How FIRES START

The exact cause of a fire or explosion in a compressor discharge sys-
tem is seldom, if ever, known. However, excessive deposits and high dis-
charge temperatures are practically always involved.
It was formerly thought that oils of very high flash point should be
used in compressors to minimize the danger of fires and explosions, but
this view is no longer accepted. The flash point of a correct compressor
oil is in the neighborhood of 400°F, but a flash point test is performed at
atmospheric pressure and the negligible quantity of vapor formed must
be ignited with a flame in order to burn.
The presence of liquid films on discharge valve surfaces, which are the
hottest parts of compressors, indicates that only negligible quantities of
oil are normally vaporized. Temperatures much higher than the flash
point would have to be reached before large amounts of oil vapor would
be formed, and still higher temperatures would be necessary for auto-
ignition of the oil to occur. (Autoignition temperatures of oil are about
750°F or more at atmospheric pressure and less at higher pressures.)
These higher temperatures could develop only from a combination of
factors. For example, a combination of recompression because of leakage
due to a broken valve and high cylinder pressure due to severe restriction
of the discharge line by deposits could cause an extremely high tempera-
ture. However, it is believed that fires or explosions may occur even
though the high temperature necessary for autoignition of the lubricating
oil is not reached.
Analyses have shown that the bulk of compressor deposits usually
consists of a variety of foreign contaminants, many of which are com-