The US DHS has identified three security issues related to chemicals:
Release—Toxic, flammable, or explosive chemicals or materials that, if released from a facility, have the potential for significant adverse consequences for human life or health.
Theft or Diversion—Chemicals or materials that, if stolen or diverted, have the potential to be misused as weapons or easily converted into weapons using simple chemistry, equipment or techniques, in order to create significant adverse consequences for human life or health.
Sabotage or Contamination —Chemicals or materials that, if mixed with readily available materials, have the potential to create significant adverse consequences for human life or health.
Guidance on chemical security and threshold limits can be found on the following link:
http://www.dhs.gov/xprevprot/programs/gc_1185909570187.shtm
Recently, the Associated Press obtained a NYPD video detailing how investigators set up a fake company that bought 300 pounds of chlorine and had it delivered to Brooklyn with little hassle or human interaction. Investigators say the operation proves there are few barriers to buying liquid chlorine and using it as a deadly gas by exposing it to air. New York City hasn't experienced a specific terror threat involving chemicals, but police recently put more emphasis on screening shipments of chlorine after learning it's now favoured in homemade bombs in Iraq.
