A Minnesota father and his five children are in critical condition after a cigarette lighter ignited a leaking propane tank that exploded inside a storage container, fire officials said.

The Minnesota Department of Public Safety State Fire Marshal (SFM) determined that the 100-pound propane cylinder, which was believed to be empty, contained enough leftover gas to fill the storage container to "dangerous levels," according to a news release issued by the state agency.

The father and his children entered the storage container in St. Paul on Nov. 4 to grab some toys, the SFM said. The children, who entered first due to the father being unaware of the impending danger, did not recognize the distinct odor of mercaptan, according to the state agency.

Mercaptan is the additive that gives propane its "gas" smell. Unbeknownst to the children and father, the spark from a cigarette lighter would set off the explosion, the SFM said.

Although the father and children remain in critical condition at a Minneapolis hospital, they are stable, according to the release.

“This family faces a long road to recovery, but they are bravely sharing their story so that nobody else experiences such a devastating accident,” State Fire Marshal Dan Krier said in the release. “We hope this family’s tragedy serves as a reminder to take precautions when storing and handling propane.”

Cold case:The boy was found in a ditch in Wisconsin in 1959. He was identified 65 years later.

'Praising God': Online fundraisers started for the family's recovery

The family of the five children created a GoFundMe and CaringBridge to fundraise money to pay for their medical bills and surgeries. They identified the children as five brothers.

The GoFundMe, organized by Kyra Frank, who identifies herself as the boys' sibling, has a $50,000 donation goal. As of Tuesday, more than $95,000 has been raised, according to the GoFundMe page.

"As many may have heard, my five little brothers were involved in an explosion. All five are in critical condition and have been life-flighted to Hennepin MN for further care," Kyra Frank wrote on the GoFundMe page. "All prayers are needed and appreciated. My mom is a single working parent and is now taking time off to be with her boys. She could use any and all the help given."

The most recent update on the GoFundMe page says the boys are stable and their vitals are "looking good," but their burns range from 5% to 55%.

"The surgeon informed us that all of them will need surgery at some point throughout this process," according to Kyra Frank. "The stays are going to be extensive and the medical bills are high as well as Mom being unable to be at work."

JaCee Frank, who identified herself as the boys' mother on the CaringBridge donation page, continues to give updates about the children, including on Monday when she announced that one of them has pneumonia.

"Praising God for the miracle all my children are! That I still have them. Despite the obstacles, I’ve actually felt hopeful today," JaCee Frank wrote on the page. "Doctors are all optimistic too. Please continue praying for these boys. They have such an uphill battle in front of them. Thank you so much!!"

What are some propane safety tips?

The SFM recommends the following tips to avoid propane incidents:

• Store propane tanks outside.  
• Never assume a tank is empty as even a small amount of residual gas can create a potentially explosive atmosphere in a confined space. 
• Equip homes, campers, fish houses and other areas with propane heating units with smoke alarms, carbon monoxide alarms and explosive gas detectors, which are available at various retail stores.

Some people may not be able to smell the odorant used in propane, making these detectors a "critical line of defense, especially for children who may not understand the significance of the smell," according to the SFM.

If a mercaptan odor is present or a detector sounds, people should evacuate the area immediately and call 911, the state agency said. Do not turn appliances or lights on or off during the evacuation because even a tiny spark could ignite the gas, according to the SFM.

Jonathan Limehouse covers breaking and trending news for USA TODAY. Reach him at [email protected].