It depends on many things... I did read a lot about this a while back so ill try and brush off some of the cobwebs in my memory and assume you are not
close enough to the blast to be vaporised
If you wish to stay in your shelter, for longer than just surviving the initial shock waves, plywood and tarp would be nowhere near good enough
I remember hearing that you would need at least 3ft of top soil above your head to offer any protection... obviously the more the better... but you
would also need to construct the shelter strong enough to avoid collapse.
Any hole in the ground needs to be supported to prevent a cave-in and involves a lot of effort... I think your best bet would to stay in your home.
First get yourself some good NBC protection... You can pick up S10's and full sealed NBC suits on ebay... in date filters are a little harder to get
hold of but it can be done... Make sure the NBC suits are still vacuum sealed before you purchase. You will also need gloves and overboots. Store all
of this somewhere safe and easily to access in an emergency along with some basic kit and provisions... Torch, wind up radio, knife etc...
Also check out some maps of your country... try to find couple of places suitable to eventually bugout to in the event of an emergency... somewhere
remote and not near any major citys or military bases.
You have about 20mins after a blast before the fallout starts to rain down on you. In the first few seconds you have to decide if you can cut and
run... or sit it out... I would base this decision on how much structural damage your home has sustained.
Assuming you decide to stay...
Find a suitable part of the building on the ground floor or basement. Kick 3 or 4 doors off their hinges (from the top floors of home) and prop them
up in a line against a main support wall (in the area you have chosen for your shelter) then pile as much material as you can on top of the doors...
If you are really prepared you will have 20 bags of builders sand you can place on top of the doors, if not... use anything, tables, suitcases full of
clothes, cushions from your sofa, soil from potted plants... anything... Seal up all exterior doors and windows with tape and board up any broken
windows. You will also need a large supply of water and enough food for 3 weeks. Keeps some jerry cans around your home full of water (although you
will need to replace the water with fresh water every 2 weeks)
For emergency food grab anything from your kitchen that is easy to prepare and has a good shelf life outside of a fridge (like tinned, vacume packed
or dried foods)
I personally have a mixture of MRE's and British army ration packs for an emergency.
Assuming you live near a major city you would eventually have to move away from the blast zone. After 3 weeks is up its time to suit up and move
out... Use your NBC gear, grab your bugout bag and hope there’s some kind of civilisation left or head to your bugout zone...
Like i said before, this is all from memory, its probably not all correct so i would strongly advise doing some research.
There is also some very knowledgeable people on this forum who im sure will correct me on a few things.
Oh yeah... one last thing... Toilet... Urrrgh!
take a bucket and some plastic bags into your shelter... place bag over bucket and use as toilet... when finished tie the bag and tape some plastic
bags over your feet.... take the bag as far away from your shelter as possible (another room if poss) Then remove the plastic bags from your feet
before re-entering your shelter to avoid contamination...
I did hear somewhere that you should puncture the bag because human excrement gives of gases which will eventually cause the bag to swell and go
pop... turning the bag into a poop bomb LOL