There are variety of unplanned events and disasters that would require you to shelter-in-place such as a tornados, hurricanes, terrorist attacks, chemical spills, quarantine and isolation.
Sheltering-in-place simply means to take shelter where you are.
Some situations may even require sealing off the room from outside containments like an explosion in an ammonia refrigeration facility across the street, or a derailed and leaking tank car of chlorine on the rail line near your home or place of business.
If a chemical has been released, you should take shelter in a room above ground level, because some chemicals are heavier than air and may seep below ground. On the other hand, if there are radioactive particles in the air, you should choose a centrally located room or basement.
Knowing what to do under specific circumstances is an important part of being prepared to shelter-in-place.
As you go about your day start to take notice of locations that you and your family, classmates or co-workers could use as a shelter. Always practice good situational awareness.
The room should either be in a basement or an interior room with at least ten square feet of floor space per person in order to provide sufficient air to prevent carbon dioxide buildup for five hours.