Googling
"shelter in place"
gets lots of hits. I live in an area with refineries, and there have been several shelter in place warnings over the years. Here are a few links to shelter in place Web sites:
http://www.nicsinfo.org/sipcenter.asp
http://www.smcready.org/Community/Shelter.html
http://www.nationalterroralert.com/shelterinplace/

These links trigger the download of .pdf files:
http://sanjoaquincounty.redcross.org/media/shelterinplace.pdf
http://publicsafety.utah.gov/homelandsecurity/documents/fs_SIP.pdf
http://publicsafety.utah.gov/homelandsecurity/documents/fs_SIPKit.pdf

I note that the Utah guides are in response to the potential for leaks from a military stockpile of chemical agents, so this page
http://publicsafety.utah.gov/homelandsecurity/csepp.html
might be of interest for those who are concerned about WMD whether by accident or intent.


My general recollection from our CERT training is that if you're in a shelter in place situation, you're better off selecting an interior room and sealing it rather than trying to seal windows and door of the whole house, along with all the HVAC ducts. We have a large walk-in closet that I'd choose - no ducts, one door, one light. (I have a bottle of Jack Daniels in there, along with a flashlight.)