May 2012

Engineering Case Histories

Case 68: Pneumatic testing dangers

Use caution on what defines a true ‘safe distance’

Sofronas, T., Consulting Engineer

I’ve written previously on hydro and pneumatic testing and how it’s an engineer’s responsibility to question dangerous conditions.1,2 Unfortunately, I still see failures and have been asked what is a safe distance to be at when performing a pneumatic test.3,4 When defining “safe distances” from a pneumatic explosion, a major concern is defining the numerous flying fragments. To understand the energy involved in pneumatic testing, the pressurized air will be treated as a compressed spring. The energy released will be used to propel a fragment horizontally. Fig. 1 shows a fictitious gas spring in a vessel with a spring constant, k, in lb/in., and compressed d, in. The

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