Federal Law & Regulations
Fire extinguishers are regulated under OSHA and the DOT regarding their manufacturing, testing, and transport. As waste, business-generated fire extinguishers might be considered hazardous under RCRA if they contain toxic chemicals (like Halon, an ozone-depleting substance banned from new production). For households, they are generally not classified as hazardous waste federally, but the high-pressure cylinder presents a physical hazard that bans them from standard municipal solid waste systems.
National Take-Back Programs
There is no single national retailer that takes back fire extinguishers. Your best option is to contact local fire equipment dealers or fire protection companies; they frequently accept old extinguishers to bleed off pressure and recycle the steel/aluminum cylinders. Some local fire departments will accept them, but policies vary widely. If the gauge reads completely empty (zero pressure), some scrap metal yards will accept the cylinder if the valve head is completely removed.