Sabotage of underwater city by a simple expedient that snowballs (as in "leaving a vent open")

I’m trying to find back a short story from probably the 50s or 60s, possibly even earlier, concerning the successful sabotage of an underwater city by a unfriendly bunch of terrorists. They had to perform a nominally innocuous action (I think it was leaving a certain ventilation flap open at the right time) to achieve full success. The simple action, together with the inhabitants’ reaction (rushing for the exit?) snowballed into a catastrophic event and successful destruction of said city.

The story is written from the point of the counter-terrorist investigators, who know there will be a hit, but they don’t know how or when it will be implemented.

I definitely read it in French, and I think it was in one of the volumes of the French anthology "la Grande Anthology de la Science-Fiction", which contained various English short stories translated to French (36 volumes, the first batch of of which was issued from 1966-1975, and the second 1983-1985).