Breaking a mercury thermometer in a room is usually fine when handled safely.
Breaking a mercury thermometer in a room can cause poisoning if it evaporates into mercury vapor in an enclosed environment. Although the amount of mercury in an ordinary thermometer is very small, once it evaporates into mercury vapor in the air, it is a highly toxic substance.
If a certain concentration is formed in a room, it can lead to inhalation poisoning. However, once a mercury thermometer breaks, if the liquid mercury is collected in a timely manner and placed in an airtight container for proper disposal, it will generally not cause serious poisoning.
The first step in breaking a mercury thermometer in a room is to promptly open all windows in the home. After opening the windows, promptly collect all the mercury, which can be scooped up on cardboard and placed in a disposable cup. Promptly remove the mercury globules outside after all of them have been removed.