The chemical virus will kill 30% of those it comes into contact with. 65% will turn into zombies. 5% of the population has a nature immunity to the virus.
The chemical virus only lasts in the air for 24 hours. During that time anyone coming into direct contact with the chemical (by touch, breathing it in or by getting it into the blood stream) will turn into a zombie provided they fall within the 65% statistic.
There are two types of zombies - "first generation" and "second generation" zombies.
First generation zombies are those that come into direct contact of the chemical virus within the 24 hour life span of the virus.
Second generation zombies are those that are turned into zombies through being bitten by any zombie type outside of the 24 hour life span of the virus.
Protective clothing, including gas masks, will prevent the virus from infecting a person. The suits must go through de-contamination before they are removed, or by waiting for 24 hours after last contact.