Investigators say the victims were part of a group of 10 or 12 construction workers having a barbeque at the KOA campground off Highway 12 in Lewis County.
One of the men came over to the campfire and showed off a powerful firework that was about 5 inches long and an inch thick. Another man tossed it into the fire, but it failed to light, so he reached in to the fire to retrieve it, police say.
A family member told KOMO 4 News another man tried to stop him from grabbing in, and in the process, the device went off.
Police say those two men lost their hand in the explosion, and suffered other head and facial injuries. They were both airlifted to Harborview Medical Center in Seattle. Both men were said to be in their early 40s.
A third man who was walking nearby was also suffered head injuries and possibly an eye fracture. He was taken to Centralia Providence Hospital.
Investigators believe the two men had been drinking.