Twenty-five firefighters were called to a health centre laboratory in Oxfordshire following a chemical leak.
A strong smell of ammonia was reported from a laboratory fridge in the Windrush Health Centre, Witney. It was then evacuated.
Three people were checked over by paramedics after breathing in fumes during the leak on Wednesday at 1500 GMT.
The fridge was removed by specialist crews who ventilated the building.
A specialist environmental protection unit was also called to the scene as well as two fire engines, before the centre reopened two hours later.
Station manager Peter Graham said: "The rapid response of the fire and rescue crews undoubtedly helped minimize the effects of the ammonia leak on this health centre allowing the centre to return to normal business, as soon as possible."