Given how frequently space junk re-enters the atmosphere, it's surprising that there is not more information about what to do in this event. So I am putting together here a small guide just in case you happen to be in this situation.
1. Don't panic: it is highly unlikely to actually fall on YOU.
You'll have heard all the commentators saying this, but it really is true: the odds of it being YOU that is the site of impact really are extraordinarily low. In the entire history of human space exploration, there is only one recorded instance of someone being hit by space junk. According to the Centre for Orbital and Reentry Debris Studies (CORDS) this was Lottie Williams of Oklahoma, who was hit by a piece of a Delta II rocket as she was taking a walk one day in 1996. She was unharmed. When Skylab re-entered over Western Australia in 1979, there were no claims for property damage made and no-one was hurt. There's just so much ocean, desert and ice - and this is usually where stuff lands. There has never been a recorded re-entry over a city or town.
The problem is, of course, that it is very difficult to predict re-entry points as there are so many variables to take into account. So it's not easy to be prepared.
But let's just say you are likely to be in the debris footprint area. Here's what you can do.
2. Secure your pets or animals
It's just like fireworks: animals don't like it very much. The fragments may be traveling at tens of thousands of kilometres per hour as they come screaming into the upper atmosphere, (which then slows them down until they fall vertically). The pieces are compressing the air into pressure waves and the energy builds up until it creates an exploding sound or sonic boom. The sonic booms can be frightening for humans too. Take the same precautions for household pets that you might on New Year's Eve. Keep them inside if possible, and remain calm around them. Don't use a chain or slip collar to restrain them. Some recommend playing them classical music (or something else soothing) as a distraction. There are many websites where you can find out more about this.
3. Do not touch fragments of re-entered spacecraft.
In its journey through the atmosphere, the spacecraft or the pieces of it are subject to extreme heating caused the friction of the atmosphere, through which it may be travelling at hypervelocity. Depending on the materials, some may still be burning when they land. Even when cool, there may be jagged and sharp edges that easily cut you.
Moreover, there are many toxic or radioactive elements that may be part of the fuel, the structures, or the experiments flown on board the spacecraft. If you handle them without knowing what you are doing, they may poison you. These include the fuel hydrazine and the metal beryllium. Let the authorities deal with it.
You're probably pretty safe with a titanium or steel pressure spheres, the most common spacecraft part to survive re-entry. However, despite titanium's traditional reputation as an inert metal, there is some recent evidence that the corrosion products of titanium may be harmful. Don't take unnecessary risks.
4. Be ready for fire
If burning fragments are falling all around you, it's not impossible that one may land on your house or the building you're in and set it alight. And when you go outside, there may be more. Do what you would normally expect to do in such an emergency: call 000 (or the fire department in your country); make sure you know where everyone is; evacuate the building (it will be safer outside) and do not go back inside. If you have a fire plan, put it into effect. This may if course involve removing animals or releasing them.
5. Notify the relevant authorities
There's a few people who need to know. Your local, regional or state government may have to play a role in coordinating relief, or recovery of debris, so let them know. It's also a matter of international relations. The country it lands in will have to notify and communicate with the launching state about recovering fragments (these are used to analyse what happened) and perhaps to talk about compensation. If your country has a space agency, they also need to know.
Debris is often found months or years later; and when it's not a high profile re-entry like Skylab, UARS or Phobos Grunt, it may not be obvious which re-entry it came from or who owned it. It's up to the government to find out. (Dr Space Junk has provided this service on occasion).
6. Assist in the scientific analysis
Your experience can be very useful. The colour of fragments falling through the sky tells us something about their temperature and sometimes what they are made of; the number and timing of falls helps map the debris footprint; the size and nature of the fragments may indicate what part of the spacecraft they came from and how it broke apart. While you most certainly shouldn't touch recently fallen material, or move it, you can take photographs and GPS coordinates, and estimate the dimensions of the pieces. What you see and experience can have some value when put together with information gathered from other sources.
7. Be aware of the legal situation
There are two international conventions that you should be aware of. One is the Outer Space Treaty of 1967, which imposes liability for damage caused by space junk on the launching state, and the other is the Space Liability Treaty 1972, which requires that the launching state pay compensation for any damage caused. I don't know, however, if that includes emotional damage - there is some latitude for interpretation. Keeping in mind safety considerations, if you or your property have been harmed by falling space debris, document it as you would for insurance purposes.
The other critical part of the Outer Space Treaty is that the re-entered material is still the property of the launching state, so you cannot sell it on eBay. In the ideal situation, the launching state will try to recover material for analysis. Be co-operative and don't try to pass fakes off as real space junk - they'll know the difference!
OK. This is very rough and ready, but it's a start. One of the sources for these recommendations is the experience of Western Australians when Skylab re-entered in 1979. It was inspired by my series of #Reentrytips on Twitter.