NEW YORK — Shawn O'Dierno's rescued Doberman was a certified therapy dog who could help soothe patients and tolerated the sounds of dropped hospital equipment, loud arguments or crying visitors. But while Reid coped with the stress of a hospital room, he couldn't handle fireworks.

"We were staying at a place by a beach where the fireworks were going on," said O'Dierno, of Portland, Ore. "He went nuts and hid behind chairs."

The situation repeated itself at other celebrations until O'Dierno realized her dog had a fireworks phobia: "His eyes would pop open, and you could see the fear when the fireworks go off."

Experts haven't figured out why some pets are extremely sensitive to fireworks, but some believe the smell of gunpowder may add to jitters caused by loud explosions.

"Fireworks have many stimulus qualities that are inherently aversive to pets," said Mary Lee Nitschke, an animal behaviorist and psychology professor at Linfield College. "The volume and suddenness of a firecracker elicits a startle reaction in most species."

Cesar Milan, dog trainer and host of the National Geographic Channel's "Dog Whisperer" show, says getting a dog ready for fireworks can take months.

At Behave Canine Solutions, a company that offers dog training classes in the Portland area, dogs in the Puppy Preschool program spend a day training for fireworks. The process involves integrating sound, smells and visual displays into activities such as playing or eating.

"What a dog is or isn't exposed to, especially in the first 16 weeks, can affect their behaviors for the rest of their lives," said Denise Mullenix, one of Behave's trainers. The class moves puppies to different stations that play sounds of fireworks, expose them to small smoke balls and burning charcoal, and bring them near sparklers and bright flashes.

Each step, Mullenix said, is designed to "minimize stress and anxiety in situations of exposure to fireworks."

Owners can also train their dogs at home. Milan plays recordings of fireworks at a low volume during an activity that the dog enjoys. Nitschke said she uses a toy similar to Roll Caps that produce an explosive noise and smell similar to gunpowder used in fireworks. You can also pop a paper bag, she said.

Continue introducing sounds of explosions for several weeks, increasing the volume with time. "Involve the sound into positive activities such as eating, at a low sound, or walking with your dog, so the dog becomes familiar with the sound while doing an activity that he enjoys," Milan said.