Many hazards are associated with pressurized air, particularly air under high pressure. Dangerous explosions have occurred in high-pressure air systems because of DIESEL EFFECT. If a portion of an unpressurized system or component is suddenly and rapidly pressurized with high-pressure air, a large amount of heat is produced. If the heat is excessive, the air may reach the ignition temperature of the impurities present in the air and piping (oil, dust, and so forth). When the ignition temperature is reached, a violent explosion will occur as these impurities ignite. Ignition temperatures may also result from other causes. Some are rapid pressurization of a low-pressure dead-end portion of the piping system, malfunctioning of compressor aftercoolers, and leaky or dirty valves.

Air compressor accidents have also been caused by improper maintenance procedures. These accidents can happen when you disconnect parts under pressure, replace parts with units designed for lower pressures, and install stop valves or check valves in improper locations. Improper operating procedures have resulted in air compressor accidents with serious injury to personnel and damage to equipment.

You must take every possible step to minimize the hazards inherent in the process of compression and in the use of compressed air. Strictly follow all safety precautions outlined in the manufacturer's technical manuals and in the NSTM, chapter 551. Some of these hazards and precautions are as follows:

1. Explosions can be caused by dust-laden air or by oil vapor in the compressor or receiver if abnormally high temperatures exist. Leaky or dirty valves, excessive pressurization rates, or faulty cooling systems may cause these high temperatures.

2. NEVER use distillate fuel or gasoline as a degreaser to clean compressor intake filters, cylinders, or air passages. These oils vaporize easily and will form a highly explosive mixture with the air under compression.

3. Secure a compressor immediately if you observe that the temperature of the air being discharged from any stage exceeds the maximum temperature specified.

4. NEVER leave the compressor station after starting the compressor unless you are sure that the control and unloading devices are operating properly.

5. Before working on a compressor, make sure the compressor is secured. Make sure that it cannot start automatically or accidentally. Completely blow down the compressor, and then secure all valves (including the control or unloading valves) between the compressor and the receiver. Follow the appropriate tag-out procedures for the compressor control valves and the isolation valves. When the gauges are in place, leave the pressure gauge cutout valves open at all times.

6. Before disconnecting any part of an air system, be sure the part is not under pressure. Always leave the pressure gauge cutout valves open to the sections to which they are attached.

7. Avoid rapid operation of manual valves. The heat of compression caused by a sudden flow of high-pressure air into an empty line or vessel can cause an explosion if oil or other impurities are present. Slowly crack open the valves until flow is noted, and keep the valves in this position until pressure on both sides has equalized. Keep the rate of pressure rise under 200 psi per second.