To fuel their 4th of July celebrations, 40 percent of Americans plan to buy fireworks, according to VISA's new national survey on Independence Day spending.

It's innocent fun for most, but for the nation's veterans suffering with Post-Traumatic Stress Disorder, they can cause discomfort and suffering.

The sound of a firecracker, the light of the explosion can take a vet right back into the combat zone, says Philadelphia VA psychiatrist Andrew Stone. One of his clients was sitting in a cafe when kids set off a few firecrackers.

"Before he could think about what he was doing, he responded with all of his training, as if he were under attack right then," said Stone. "And his coffee went flying and he went under the table, he was quite embarrassed by that."

Stone says other reactions include severe anxiety and discomfort. He says many vets avoid fireworks and 4th of July celebrations because they are afraid the sights and sounds will trigger unwanted memories or reactions.

"In order to stay out of trouble, they stay out of life," said Stone. "If you stay home and don't go out, you won't get into difficult situations, but you miss out on the entire world." Stone encourages vets are struggling with PTSD to seek help. "If people are noticing they are having these reactions, and it's limiting their lives, they should know that there are things to do about it."

Stone says PTSD treatment is very effective, and with time, people with PTSD can get to a point where they can enjoy activities such as going to see fireworks again. The tougher situation is when a small explosive goes off in an unexpected place.  Vets can prepare themselves when going to watch a fireworks display, but may fall back on their training and survival instincts in incidents such as the one at the cafe.