You can skip the thermal calculation to select Arc Flash PPE but there are still a few things to consider:
In case of an arc fault in the pressure vessel of the SF6 switchgear there are dedicated pressure relief openings (rupture disc) that open at a specific overpressure. They then vent the hot gasses of the pressure vessel via dedicated ducts within the switchgear. These can be open on the top or bottom so the hot gasses will eventually come out of the switchgear. Usually they vent down into the raised floor/cable floor. One major thing to consider there is that the floor panels have to be closed all around and are properly secured so they dont get lifted by the overpressure that comes from the heated gas!
There has been at least one accident reported with SF6 switch gear where the operator would operate the last panel of the switchgear (close to the side wall) where the floor was not properly closed next to the panel.
During the switching an arc fault occured and the hot gasses eventually found their way to the operator and caused burns. See here for a google translated version of the accident report
Another thing to consider is, that during type tests of switchgear (no matter if SF6 or air insulated or even MV/LV) the heat is never measured! They only test (among other criteria not related to heat) if test pieces of cotton fabric ignite or not. Depending on the IAC classification this is tested at the front, side and/or rear.
A typical test setup looks like this:
So our recommendation is always to wear at least long sleeved cotton fabric clothing and perhaps safety glasses and gloves.
As Mike already pointed out you also have to double check if your short circuit current and switchings times are below the max values of the IAC test. A typical value for arc rated switch gear would be 16 kA / 1 s
Last but not least you should always consider the pressure rise in the building. It is a requirement by IEC 61936-1 and should be done before erecting the switch gear. Especially with weaker brick wall switch gear rooms you typically need large pressure relief openings or ducts on the switch gear that vent the pressure from internal arcs directly to the outside.