The rescue mission came after police were called to the home in Quebec City's Charlesbourgh neighbourhood Tuesday night to respond to a problem with an alarm system.
When they showed up, they found a filthy house with more than two dozen cats inside, and the floors covered in urine and excrement.
"The levels [of ammonia] are way above what is considered acceptable in a residential environment — high enough to pose a health hazard," said Jean-François Daigle, spokesman for the Quebec City fire department.
An acceptable level of ammonia is 1.7 parts per million (ppm). Ammonia levels in the home were registered at 240 ppm. A level of 300 ppm can be fatal.
Firefighters had to wear breathing masks and protective suits to inspect the premises.
Animal protection services had to wait nearly a day to carry out their rescue operation in order to air the house out and to obtain the proper protective gear to be able to go inside.
The man and woman living in the home were sent to hospital for a check-up.
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