ennui03,
You can consider H2 buffer drum PSV tailpipe service as Hydrogen. However considering overall scenario, if buffer drum is part of any Hydrocarbon treatment facility, you need to design flare system by giving priority to process complex requirements.
Beyond this, there are some peculiar characteristic that H2 follow like...
a. H2 flame is practically invisible ,
b. H2 has very low ignition energy requirement, hence it can catch fire easily in normal Process plant environment.
c. At high pressures, H2 does not follow JT effect and heats up when expand...
considering impact of such special characteristics, please analyse overall process system & flare system considering H2 presence and provide mitigation measures required, if any.