I do not see any connection between Fire pump running during fire and other loads running. It depends on the following factors.
(1) Is the fire is isolated in one building ( if there are other buildings in the same area). Then ( if isolated) other loads can be run in other buildings.
(2) Even in the same building if the Back up DG set can take up the Fire Pump load and other essential loads it is Ok. People can use the lifts etc if the fire is far off.
Generally power is switched off as a precautionary measure . Some times there is a
Basically the fire pump is a part of sprinkler system and can be powered by electric, diesel or steam. Some local building code requires power independent of the local power grid, a pump using electric motor may utilize.
Installations I have done in my local depending on which code is followed i.e. NEC, CEC, or other state, county, local municipality require a separate service (electric utility) independent from building main service.
Depending on the code that applies, if installed in a dormitory, hall, parking facility, church, hotel, school, fire/police facility, hospital, auditorium, theater require a separate independent service (electric utility) from building main service and a generator
In any case, my experiences have been that an independent service is required as a minimum.
To answer your question, there would not be any additional loads on a fire pump service other than the fire pump therefore other loads being on while the fire pump is running is a moot issue.
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