Ignition of flammable hydrogen/air mixtures by mechanical stimuli. Part 2: Ignition under conditions of rust and surface pyrophoric material contamination

Ignition of flammable hydrogen in air (and other H 2 /N 2 /O 2 mixtures) by mechanical stimuli. Part 3: Ignition under conditions of low sliding velocity (<0.8 m/s)

“…The ignition frequency results obtained using mechanical loading of 1000 and 2500 N with sliding velocities in the range 0.8 to 0.34 m/s are shown in Fig. 2: for convenient comparison, these are shown together with the results obtained previously for mechanical loading in the range 20e260 N [2].…”

“…Ignition frequency with high mechanical load and low sliding velocities e magnesium/rust thermite reactants on the surface A series of experiments was conducted in a manner similar to that described earlier [2]. Test surfaces were prepared using a milling technique to produce "medium" grade smears of magnesium on heavily rusted steel plates.…”

“…In part one [1] it was reported that ignition of flammable hydrogen/air atmospheres can readily occur through friction generated by sliding clean metal surfaces when high load conditions are involved. In part two [2] it was shown that ignition from the mechanical action is very much easier when metal surfaces are contaminated with a pyrophoric substance such as magnesium. Ignition becomes possible with very much smaller mechanical loading and at lower velocities than for clean metal surfaces where the ignition mechanism involves the generation of hot surface areas.…”

“…Because the generated surface temperature and likelihood of ignition should theoretically vary with loading proportional to the fourth root, it is expected that considerably higher loads may be required for ignition than previously employed in experiments [2]. To investigate this, requires the development of a test apparatus to provide constant low velocity movement between the contacting surfaces at high loads.…”

“…There are considerable practical difficulties in carrying out sliding friction experiments under low velocity conditions due to the likelihood of Jerky-slip friction effects [1,2].…”