A party turned tragic this weekend when candles from a birthday cake caused fire to erupt in the basement of a bar in France.

The country of France is on high alert due to several terrorist attacks that have taken place on their soil. Eighty-five people were killed in the terrible attack in Nice on Bastille Day (July 14); one hundred thirty people were killed in the Paris attacks at the end of last year; and a priest was stabbed to death by Islamist extremists during church services just outside Rouen on July 26.

As a result of the high alert, when neighbors of the Au Cuba Libre bar in Rouen heard what they thought to be a blast, people feared that another terrorist attack had taken place.

[Photo by Kamil Zihnioglu/AP Images]According to The Guardian, Lawrence Labadie, the deputy prosecutor in Rouen, told a primarily French-speaking publication that the blast neighbors heard was actually glass from the front window exploding from the heat of the fire.

He went on to say that there were no explosives, "but candles used for a birthday party set light to the ceiling made of polystyrene, giving off a gas that poisoned the victims."

Officials believe that what started the fire was an unfortunate accident. The person holding the birthday cake was walking down the stairs. The candles were already lit and the person tripped, causing the cake to fall.

The fire spread incredibly fast.

Yvon Robert, the mayor of Rouen, told the Associated Press that the fire was "very brief."

The fire started on the floor, spread to the walls, and finally reached the ceiling where the polystyrene ceiling tiles became fuel for the flames.

[Photo by Kamil Zihnioglu/AP Images]Polystyrene is significantly flammable, and when it burns, it releases noxious gas into the environment. Although people on the ground floor of the bar were able to escape, the fire and poisonous gas consumed everyone present at the birthday party in the basement.

World News Online reported that a witness was able to speak to a television station in France about the birthday party fire.

"Everybody wanted to get out," the witness said. "Unfortunately, those who were in the basement didn't have time to get upstairs."

Firefighters were quick to respond to reports of the fire. Roughly 50 firefighters showed up on the scene. Together, officials were able to control and extinguish the fire before it spread to any other structures, but the damage had already been done.

[Photo by Kamil Zihnioglu/AP Images]Thirteen young adults were killed in the birthday party fire. All of those victims were between the ages of 18 and 25. The majority of the birthday party guests that were killed, however, did not die as a direct result of the fire. Instead, they died from inhaling the noxious gas produced when the polystyrene ceiling tiles burned.

Polystyrene insulators are prohibited in many public venues in many places, including France. The material is incredibly toxic, especially when involved in a fire. BBC reported on two different incidents in the past where a fire occurred in public places with deadly results. In 2013, there was a fire in a club in Brazil that killed upwards of 240 people. Last year, a fire in Bucharest killed 27 people.

Polystyrene insulators were responsible for the spread and fatality involved in each fire.

French officials are investigating, but it is currently unknown whether or not they will be charging the owner of the bar.

[ Photo by AP Photo/Kamil Zihnioglu ]Prime Minister Manuel Valls issued a tweet to explain the country's grief for those lost in the birthday party fire.

Incendie grave à Rouen : profonde tristesse face à la tragédie qui a fauché 13 jeunes vies. Compassion et soutien aux familles éprouvées.

— Manuel Valls (@manuelvalls) August 6, 2016

The translation of the tweet is, "Serious Fire in Rouen: Deep sadness with regard to the tragedy that mowed down 13 young lives. Compassion and support for the afflicted families."

[Photo by Kamil Zihnioglu/AP Images]