[header] How to make a gas mask [title] Know the difference between gas and particle contamination. [step] Tear gas is actually a dust that is sprayed into the air, whereas biological weapons are generally gases. While it is incredibly difficult and expensive to completely protect yourself against gases, you can easily create a barrier against particles at home. 
[substeps] Toxic ash from volcanoes, tear gas, and dust are all particle contaminates. [title] Cut the bottom off of a transparent 2-liter soda bottle.