PVC Pipe Dangers Debunked
4-in.-dia. plastic duct is unlikely to cause a static-induced blast in a home shopSynopsis: Home-shop dust collection is a controversial topic, primiarily because of the safety of PVC pipe in this application. Some claim that sparks in PVC pipe due to static electricity may ignite the dust cloud in the pipe. Others speak up for grounding the pipe, thus ensuring safety. Rod Cole consulted scientists at MIT to discuss the physics and ferret out the truth.
Home-shop dust-collection systems have become increasingly popular, but their safety has been hotly debated. The primary issue is whether PVC pipe is safe for use as ductwork. Many claim that sparks in PVC pipe due to static electricity may ignite the dust cloud in the pipe. The specter of a giant fireball consuming a shop and home is repeatedly raised. Others claim you can ground PVC, thus ensuring its safety.
Two years ago I had to decide for myself: PVC or metal ducts for my basement shop. Being both an avid woodworker and a scientist, I made a concerted effort to understand the issues. Fortunately, I have the resources of the library at the Massachusetts Institute of Technology (MIT) and a professor just down the hall who’s an expert in the physics of lightning.
I studied static discharge from insulators, as well as the more general topic of dust ignition. I found that it’s extremely unlikely for a home-shop-sized system to have a dustcloud explosion. Commercial-sized systems have had dust-cloud explosions, but different phenomena come into play in larger systems, and 4-in.-dia. PVC is too small for use in such systems, where the airflow is much greater than in a home shop.
Sparks are unlikely in 4-in.-dia. PVC pipe
In my research I turned to the Journal of Electrostatics, a publication that covers the effects and interactions of static electricity, particularly in commercial applications. This journal has published a number of studies on the combustibility of dust clouds by electrostatic sparks. The researchers were able to determine some of the conditions necessary to create sparks and ignite a dust cloud.
Sparks can be caused by a variety of conditions—one of which is static electricity. However, sparks are unlikely inside a standard 4-in.-dia. PVC pipe that would be used in a home shop, and more importantly, any such sparks are extremely unlikely to be strong enough to cause an ignition. I can’t say it is truly impossible, but it is very close to impossible, and I do not know of a single instance.
From Fine Woodworking #153
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