More and more blasting contractors are making the switch to low-pressure respirators. A high-pressure respirator requires an air source of 6 to 15 cfm at 65 to 100 psi. Some contractors connect their high-pressure respirator to the same compressor that supplies the blast air. A low-pressure respirator requires just 8 to 15 psi, but still maintain 6 to 15 cfm of air flow. Low-pressure respirators receive air from an ambient air pump, which draws in fresh air from wherever it is located and sends it to the respirator. As such, the pump should be located upwind from the blast operation, and well away from any area where vehicles may pass by or stop and idle. Whichever respirator model is used, it must be supplied with Grade-D breathing air. It's always a good idea to install a carbon monoxide monitor/alarm as a measure of safety.
Because of concerns about the quality of air they produce, many compressors bear labels warning that they must not be used for breathing air. If you find yourself renting a compressor, where its maintenance and operating history is unknown, or if your own compressor seems suspect, you should look into buying an ambient air pump and low-pressure respirator.
Owners of high-pressure Apollo helmets can save money by converting them to work with an ambient air pump. While high-pressure and low-pressure helmets share many components, be very careful to use the system exactly as designed. Swapping air fittings or hoses can lead to trouble.
The internal passages in Clemco's low-pressure systems are engineered to allow sufficient air volume to maintain positive pressure in the helmet. In fact, the passages in the fittings are substantially larger in internal diameter compared with those in our high-pressure systems. Just one restriction in a low-pressure system can choke your air flow to a trickle, eliminating any protection from dust.
Even the length and composition of the air supply hose are critical. The hose is fabric-reinforced neoprene that resists kinking. It is made with special non-toxic mold-release agents. Clemco's low-pressure systems normally come with 50 feet of hose, the minimum allowable length; but can be used with up to 300 feet of hose, when a maximum of three 100-foot sections are coupled together. It's important that there are a maximum of three connections points as each connection can represent a reduction in air flow. Pressure loss is inherent in all air lines, so Clemco engineers have factored in that loss.
Remember, OSHA has made it clear that the employer bears responsibility for providing a "safe and healthy workplace free of hazards". Maintaining and operating your safety systems by the book go a long way toward satisfying OSHA's requirement and protecting your operators.