arpadveress 
It has been demonstrated experimentally and numerically that accidental releases of pressurised hydrogen are prone to spontaneous ignition. The actual causes of ignition could include electrostatic and corona discharge; mechanically generated sources; diffusion ignition due to shock heating and catalytic ignition. It is also recognised that two or more of these mechanisms could be present together.
This is a cut out from a recent study circulated in the EU.
EN 1127-1 says possible ignition sources might be:
– Hot surfaces
– Flames and hot gases (including hot particles)
– Mechanically generated impact, friction and abrasion
– Electrical equipment and components
– Stray electric currents, cathodic corrosion protection
– Static electricity
– Lightning
– Radio frequency (RF) electromagnetic waves from 104 Hz to 3 × 1011 Hz
– Electromagnetic waves from 3 × 1011 Hz to 3 × 1015 Hz
– Ionizing radiation
– Ultrasonic waves
– Adiabatic compression and shock waves
– Exothermic reactions, including self-ignition of dusts
Ex personnel competency shall be a key issue even when making studies. Topic hydrogen is trendy today, but it is still explosive in many ways.
Keep up good work!
Arpad
