Explosion in testing equipment

During a test in which GH2 was driving gas, an explosion occurred in the test section. The drive chamber was over-pressurized to 3500 psi (240 bar).
The test section failed; windows designed for a lower pressure release failed and the walls, which were covered with wall board, ignited causing more damage.

[Ordin, NASA (1974)]

Window in test section failed due to excessive pressures. A higher pressure was obtained than calculated due to choked flow conditions in the tube.

unknown

EXPLANATION OF 'CHOCKED FLOW'
Choked flow is a condition in which the flow rate of a fluid becomes constant, regardless of any further increase in the pressure drop across a restriction.

[https://en.wikipedia.org/wiki/Choked_flow]
"Choked flow is a compressible flow effect. The parameter that becomes "choked" or "limited" is the fluid velocity.
Choked flow is a fluid dynamic condition associated with the Venturi effect. When a flowing fluid at a given pressure and temperature passes through a constriction (such as the throat of a convergent-divergent nozzle or a valve in a pipe) into a lower pressure environment the fluid velocity increases. At initially subsonic upstream conditions, the conservation of energy principle requires the fluid velocity to increase as it flows through the smaller cross-sectional area of the constriction. At the same time, the Venturi effect causes the static pressure, and therefore the density, to decrease at the constriction. Choked flow is a limiting condition where the mass flow cannot increase with a further decrease in the downstream pressure environment for a fixed upstream pressure and temperature."

test equipment destroied and building damaged