(Full Guide for biological and chemical agents is below the first section on the emercengy mask)

Prepare an EMERGENCY gas mask

Required:

Cotton fabric (a bed sheet is ideal)

Baking soda (sometimes called baking powder)

Sewing kit or strong duct tape (if you use tape, it has to be at least 2 inches (5 centimeters) wide)

Method

Cut two squares of fabric, around 6 inches (15 centimeters) squared. Sew or tape up three of the sides of the two square together to make a pocket and pour in the baking soda (enough to form a good layer over the whole area of the square), then sew or tape up the last edge. If you use tape, it is a good idea to use a few layers per edge and then a few small squares of tape over each corner. Check your finished square by laying it on a flat surface and shaking it to spread the baking soda inside evenly, you should be able to feel the layer of baking soda if you have added enough in. Keep your new temporary mask in a safe place and carry it around, along with a bottle of water for the mask usage, wherever you go. Goggles or glasses (or sunglasses) should be carried too for at least some level of eye protection at all times.

Use:

If you fear a chemical attack is happening, dampen the square and even out any lumps of soda. Press the square firmly over your nose and mouth and leave the area as quickly as possible.

THIS MASK IS ONLY FOR TEMPORARY, EMERGENCY USE. IT IS NOT TO BE USED MORE THAN ONCE FOR ANY REASON. IT IS ONLY EFFECTIVE FOR A VERY SHORT TIME AND MUST BE RESPONSIBLY DISPOSED OF. IT WILL POSE A SIGNIFICANT HEALTH HAZARD AFTER USE.

PLEASE REVIEW THE GUIDES BELOW ON BIOLOGICAL AND CHEMICAL WEAPONS INFORMATION THOROUGHLY FOR ADVICE REGARDING DIFFERENT CHEMICALS AND PRACTICES FOR DISPOSAL.

The most useful parts of the below guides are the last few APPENDIX pages in table form