JEFFERSONVILLE, Ind. -- Stationed in Khandahar, Afghanistan, for nine months in 2012, Sgt. Matthew Thomason got used to falling asleep to the lullaby of gunfire and explosions -- so much so that he could tell what kind of weapon was being fired just by the sound. When he returned home to Clark County in September 2013, he thought he would miss the noise of war as he transitioned back to the quiet civilian world.

The first time he heard the crack of fireworks around July 4 the following year, he realized how wrong he was. Thomason, a 28-year-old Louisville native and Sellersburg resident, remembers being at that first Independence Day party when a flashback was suddenly triggered. He was either playing a game or in a conversation with his wife -- he can't remember which -- when someone behind him set off fireworks without warning.

"When that happened, I physically just jumped and didn't really know where I was for a minute," he said. "I had a flashback and we had to leave, and that started to be a trend."

Several months prior, Thomason was diagnosed with post-traumatic stress disorder, or PTSD, at a local U.S. Department of Veterans Affairs clinic. He was later diagnosed with traumatic brain injury, though he doesn't know which explosion did it. Now when July 4 comes around, he and his wife go out of town, somewhere like the Smoky Mountains where Thomason can find peace and quiet. And he's not the only one.

Thomason is one of an estimated 11 to 20 percent of veterans of the post-9/11 Iraq and Afghanistan wars diagnosed with PTSD, according to data from the U.S. Department of Veterans Affairs. While fireworks don't trigger PTSD for all soldiers or veterans, it seems to be a more common occurrence in recent years. Cindy Ramminger, coordinator of the PTSD clinical team at Robley Rex Veterans Affairs Medical Center in Louisville, said fireworks were an issue for veterans from as far back as the Vietnam and Gulf wars.

But with so many soldiers coming home from the wars in Afghanistan and Iraq it's becoming a bigger problem, Ramminger said. It's not uncommon for her to hear of veterans leaving their homes on the very holiday they fought in the name of, just to escape the noise.

"It can remind them of what might sound like an incoming rocket or mortars or gunfire, which can cause them to get on alert and it can cause them to be frightened," Ramminger said. "It can push them into a flashback (and) can cause intrusive thoughts, so they'll start remembering a traumatic event like when they got blown up in an IED attack or lost a friend to some kind of explosion."

Thomason said as a solider, he was repeatedly trained to react quickly and defensively when there was a perceived threat. So when he unexpectedly hears fireworks in the weeks leading up to July 4, his body immediately jumps to attention. Unlike what you'll see in the movies, Thomason said his flashbacks aren't necessarily visual. It's more about the smell of the powder left behind by fireworks, a smell similar to a freshly fired M4.

He calls it an overwhelming "feeling of terror."

Thomason has found ways to cope, like making sure his back is against a hard structure when he's feeling unsafe. Breathing exercises help, too, but those tactics don't always work. Sure, he can leave town on July 4 to avoid the triggers, but what about the days leading up to then? Thomason said his terror starts as early as May as people start stocking up on fireworks and setting them off unexpectedly.

Shawn Gourley, the co-founder of Military with PTSD, a nonprofit organization based in Evansville, said that's the issue many veterans have with early fireworks. Gourley started a Facebook page in 2010 to help spouses of veterans and later created a website with resources for couples and families. Last year, a member shared a photo of a sign he created to put in his front yard that read, "Combat veteran lives here. Please be courteous with fireworks."

The photo got millions of shares, Gourley said. She asked the member if the organization could mass produce the same sign and send them out to veterans. The member said yes and before she knew it, Military with PTSD had sent out more than 4,000 signs to veterans across the country — at no cost to the veterans. This year, the organization has sent out more than 1,600 signs. Different signs for supporters of the cause, including civilians, are now available on the website for a fee.

Gourley said the signs have helped veterans start discussions with neighbors. A knock on the door and a heads up that someone plans on setting off fireworks can make a big difference, she said. For the neighbors, the signs show them a way to help the people who served their country.

"It isn't to stop fireworks. What it is, is any day leading up to July 4 and the days following July 4. If you're going to be setting off fireworks, if you could just give the veterans a heads up. It's the unexpected fireworks that is what bothers them, what can trigger (PTSD)."

In Indiana, state statute allows for fireworks between 9 a.m. and 11 p.m. year round and until midnight on holidays like July 4. Local ordinances can limit when fireworks are allowed, but state statute trumps those ordinances between June 29 and July 9. During that timeframe, local municipalities can not restrict fireworks use beyond the statute.

In Sellersburg, where Thomason lives, an ordinance prohibits all fireworks during the rest of the year. Town attorney Jake Elder said the council planned on adding an ordinance to make exceptions during July 4 season to the meeting agenda for Monday's council meeting. Elder said town officials thought such an ordinance already existed.

Thomason said he's called Sellersburg police about fireworks being set off as early as June 1, but he said he hasn't gotten a response. Police Chief Russ Whelan said he is not aware of any complaints pertaining to fireworks triggering PTSD. Whelan added that the department looks to state statute when regulating fireworks in the town.

Indiana Rep. Steve Stemler, D-Jeffersonville, said he's not aware of any talk about amending state statute in light of the issue. But he said anything that could help veterans dealing with PTSD should be considered.

Thomason said he doesn't want to ruin anyone's fun. Putting a sign in his yard isn't for him, and he knows many veterans who are embarrassed even to talk about their PTSD.

"I think a lot of people would like just more understanding and more respect. There's no need to be setting off fireworks consistently before Fourth of July," Thomason said. "Because going to that place in my head on a regular basis for two months is really a tortuous thing."

Gourley said she understands that not every veteran wants a sign in their yard, but she thinks finding a positive way to confront triggers is better than avoiding them. And beyond that, she said the signs have inspired appreciation. One veteran told her that after putting a sign in his yard, a woman showed up at his door with a bouquet of flowers and a thank you.

Scott Ham, a retired command sergeant major with the Indiana National Guard who lives in New Albany, said he doesn't have PTSD and isn't triggered by fireworks, but he knows vets who are. He said it's important for loved ones to be respectful of those veterans who are triggered by fireworks.

"All of my friends that I know that have issues with it, have all said that it seems like their friends and family insist on pressuring them that it will be OK," Ham said. "But the last thing you want to do is put someone in that position when you don't know what the potential outcome could be."

Thomason, who was medically discharged in February, said his symptoms have gotten easier to manage, but he thinks they'll always be there to some extent. He's now able to work part-time for a New Albany-based piping fabrication company, though he often works from home where he's confronted with fireworks three to four times a week in June. On the Fourth, he may not hear the fireworks or see the colorful display in the sky, but the holiday still represents what he fought for during those 10 years of service: a country where everyone is treated equal.

"That's the America that I fought for, where we have freedom to choose, and we're not discriminated against or put down because of anything," Thomason said. "So for me it still means that. The only thing that's truly changed is how I celebrate it."