A dog’s sense of hearing is significantly greater than a human’s. Studies have shown that dogs are capable of perceiving frequencies about twice that of a normal human and can pick up and distinguish sounds roughly four times that of humans. This means that dogs can hear many sounds on frequencies that humans cannot even begin to detect and what a human can hear at 20 feet a dog can hear at roughly 80 feet.
That's from ServiceDogCentral.org.
Imagine how loud a simple firecracker is to our furry little friends. Please remember: Pets and fireworks don't mix.