Flight detent, Whilst the fire station may be situated near 21L, my experience is that response time is anything but quick. The language difficulties make communicating what you really want quite difficult. Consider the following... you are starting an engine at the gate, and the ground engineer reports "tailpipe fire". Honestly, would your immediate actions include sending a "Pan" call to the ground controller, or something less urgent, perhaps to the effect of "callsign ___ tailpipe fire, stand XXX, standby for intentions" ? (typically a tailpipe fire will extinguish when the fuel is cut) If you chose the latter option, it would have taken numerous radio calls to get the message through to ATC, coupled with stepping on each other and ATC approving the aircraft at the adjacent bay to push in the meantime! Yes, this incident happened around 10 years ago there.
It is also not apparent if the United aircraft was tankering fuel to Tokyo .This would increase its GTOW significantly.
Bangkok is the worst airport in the world that I operate in to w.r.t .communications, both the quality of the controllers and their equipment. Regularly the ATIS is appended with "controller training in progress" (if you can understand the ATIS at all!)