The US scheme is pretty complicated, with lots of overlap between state and federal agencies and, national security issues to address.
I know I'm not the one to elaborate because Americans know way more about this than I do, but here it goes:
The Basic (Federal) Players -- NIOSH which is under CDC which is under DHHS; OSHA which is under DOL; DOT which has several agencies ; and EPA.
At the State level, there are numerous cascading branches of Public Health, Commerce (and/or Labour), and Environmental Departments, many of which have overlapping responsibilities and boundaries. The differences between 'enforcement', 'authority' and 'resource' become pretty significant when Local, State and Federal lines get crossed.
Confused? I bet it is a nightmare for some of there safety managers.
Knowing where one stands can be quite challenging at times.
and to cap it all the links have not worked, but if you go to niosh there are links from there
http://www.cdc.gov/niosh/homepage.html
http://www.hhs.gov/
http://www.osha.gov/
http://www.dol.gov/
http://www.dot.gov/index.cfm
http://www.epa.gov/epahome/pestoxpgram.htm
