If you think about the type of environment a crawlspace under the home creates it’s easy to see why there would dangers down there. In general, they are damp, dark places that often go undisturbed for long periods of time. These conditions are perfect for many kinds of insects, rodents, and animals, some of which may be poisonous. Be aware also that if a creature feels threatened or cornered, the situation could become dangerous. In a tight space like this, it could be difficult to get out of the way quickly.
It is not just insects and rodents you will want to watch out for, additional hazards such as mold, fungi, standing water, and even sewage are all found in under the home crawlspaces. All of these things are well known to be dangerous if exposed to them so it's clear to see the need to be extra careful when in close proximity to them.
If you suspect the property has sustained any structural damage then it is best to avoid entering the under-home crawlspace altogether, at least until you know the type of damage you are dealing with. The wisest course of action in this situation is to have the home professionally inspected first.
How can you prepare yourself to enter an under-home crawlspace? Firstly, make sure you are wearing protective clothing and appropriate equipment before entering the space. You will also want to have someone else at the home with you who knows where you are and what you will be doing down there. This way, they can provide assistance or get help if you run into any difficulties.