Brentwood Fire & Rescue now carries pet-sized oxygen masks on its trucks after receiving five donated kits in October.

The kits, provided free through Invisible Fence Brand's Project Breathe program, each include small, medium and large reusable masks shaped to fit an animal's snout, as first reported by WKRN. Each kit also comes with oxygen tank tubing, a slip lead and an instruction sheet, according to Invisible Fence Brand.

Standard human oxygen masks do not fit animals. That gap matters because pets caught in house fires tend to hide in enclosed spaces rather than run for an exit. The behavior prolongs their exposure to smoke and toxic gases, Brentwood Fire & Rescue said in an Oct. 21 Instagram post.

"Since standard human oxygen masks aren't shaped to fit an animal's snout, these masks will help us deliver oxygen to pets in emergencies," the department said.

An estimated 40,000 pets die in U.S. house fires each year, most from smoke inhalation, according to the American Veterinary Medical Association and the National Fire Protection Association. Roughly 500,000 more are affected.

The masks are part of a broader national push. Project Breathe launched in 2006 and has donated more than 27,000 masks to first responders across the U.S. and Canada, according to a Sept. 30 press release from Invisible Fence Brand. The company relaunched the program this year to mark its 20th anniversary and National Fire Prevention Month in October.

As of late September, more than 30 upgraded kits had been donated to fire departments through the relaunch, including departments in Naperville, Ill., and several in Indiana and Ohio. Brentwood Fire & Rescue received its kits in October.

John Butrim, executive general manager at Invisible Fence Brand, said in the press release that the company is reconnecting with fire departments in communities served by its local dealer network. The kits are produced in partnership with Pawprint Oxygen and feature masks compatible with equipment already carried on fire trucks and ambulances.

Fire departments interested in requesting a Project Breathe kit can submit a request at invisiblefence.com/o2, according to the company.