In case it turns out there is Ex hazardous area, it exists, shall we look for ignition sources if that hazardous area was not identified earlier?!
Whose responsibility to ask for? Lucky situation if MSDS defines combustible in certain circumstances, BUT who shall take care for it? Customer or supplier of design, installations and all around?
In that case BOTH.
I personally do face situations where disagreement intends to rule the current scenario, and all involved do not see the way out.
Better to be pro-active and preventive. Ex safe operation is not easy to achieve and handle, but to realize on later stage barely impossible.
Keep up good work!