Detonation in the piping system of a testing facility

A stainless steel manifold ruptured during experimental operation. The manifold was made of stainless steel and had a diameter of three inch (7.5 cm). The hardware was off-the-shelf, slightly modified, pre-safety checked and analysed by the supply vendor. The test apparatus was in an altitude tank at simulated altitude conditions at the time of the mishap.

At the moment of the explosion, it contained a mixture of hydrogen (0.27 lbs, 0.12 kg) and air (0.26 lbs) at 350 psia (24 bar). Damage was restricted to the manifold and some of the experimental package valves.

The INITIATING CAUSE of the rupture was a detonation of an accidentally formed hydrogen and air mixture inside the manifold.

The investigation team determined that the principal cause of the mishap was the lack of backflow prevention devices in the hydrogen and air supplies to the test package. That deficiency permitted the accumulation of the detonation charge within the manifold. A contributing factor was the deviation from preplanned test procedure by the test crew while attempting to make the device work.

manifold, valves

Damage was restricted to the manifold and some of the experimental package valves.

The source report the following lesson:
Even a "Small amounts of hydrogen and air (much less than a kg) and an ignition source can cause detonation and damage in a confined area."

The source recommended following:
"Design backflow prevention devices in propellant piping systems to prevent the accumulation of combustible mixtures in confined areas."