When Hughes Environmental technicians work on a combustible dust cleaning job they use certified explosion proof vacuum cleaners that the NFPA and OSHA require. These vacuums are designed to use compressed air to create a vacuum, and do not have a motor or moving parts that can create sparks or static electricity.
Most people assume that these are just like a larger version of a household shop vac, but they actually use a completely different method of creating suction. Instead of a motor spinning a blower fan to create suction, our explosion proof vacuums have compressed air blown into them, which creates a vacuum effect.
How does blowing air into the vacuum create suction? These industrial vacuums make use of the Venturi Effect, which is caused when a constriction in the air passage causes the air to speed up and slow down again. When it passes through the constriction it creates low air pressure, resulting in a vacuum. The suction created by the Venturi Effect is significantly more powerful than anything an electric vacuum can produce, and it is all done with no moving parts or dangerous electrical cords.
In our explosion proof vacuums the compressed air is blown into a chamber (A), where it is then forced through a compressing nozzle (B). Being forced through this nozzle caused the air to speed up significantly, where it then enters the mixing chamber (C) and the air velocity slows back down. This slowing down of the air velocity creates negative air pressure, which is used to create suction for the vacuum hose (D). This mixture of compressed air and vacuumed air/debris then goes through a high quality filter (E). In our vacuums the compressed air creates negative pressure inside the metal drum, which then creates suction an attached hose, but the idea is the same as in the diagram.
A 2012 report by the NFPA showed that between 2006 and 2010 there were over 8,600 fires in industrial or manufacturing buildings. Dust was determined to be the cause of ignition on 12 percent of these fires, which means at least 1,032 fires were caused by combustible dust.
