A design condition for vent stacks is to always assume that the hydrogen will ignite. The stack musts be designed such that it can withstand those conditions as well as minimize radiation to surrounding personnel and exposures. Although hydrogen fires have comparatively low radiation compared to hydrocarbon fuels, the radiation from large releases from vent stacks can be quite high. Documents such as NFPA 2 and API 521 provide direction on acceptable levels of radiation for different exposures. Also, the temperature of the flame is very high, so if the hydrogen flame contacts materials around the vent stack, they are likely to melt or ignite.