Mainers use propane to fuel outdoor grills, indoor appliances — like stoves and clothes dryers — and to heat homes and buildings. Sold in tanks outside gas stations and grocery stores, the flammable substance can be found all over the state. Propane is the second most common home heating source in Maine, with just under 14% of homes using it for heat in 2023, according to the latest available data from the U.S. Energy Information Administration. While that’s more than three times the national average, it’s still a major step down from heating oil, which is used in more than half of Maine homes. That figure excludes people who buy propane for their outdoor grills or recreational vehicles, meaning propane usage is likely much higher. While the flammable gas is generally considered safe if used correctly, it can be hazardous if improperly handled, leading to fires and explosions. Maine has seen a number of those incidents in recent years, including over the weekend, when two women died after their camper exploded in Old Orchard Beach. In 2019, a propane explosion in Farmington killed a fire captain and injured at least six others. Here’s what to know about handling and maintaining safe propane systems: When is propane dangerous? How does it differ from natural gas? While both can be dangerous if inhaled or ignited, propane is more likely than natural gas to settle in a given space, said Wells Fire Chief Mark Dupuis, who worked in the propane industry for more than six years before joining the department. Natural gas is lighter than air, meaning it dissipates into the atmosphere in an open space; but propane is denser than air, so it settles on the floor and in enclosed spaces — “kind of like you’re filling up a tub with water,” Dupuis said. “In a grill, it will settle in the base of that grill, and if you (attempt) to keep lighting it and it’s not lighting, and all of the sudden it does, it’s going to be a big blast of fire in your face,” he said. What are the warning signs of a propane leak? The key indicator of a propane leak is its smell, Dupuis said. “Propane is odorized,” he said. “People think it naturally stinks. It does not.” But it may be difficult to smell the gas in some cases, according to the Propane Education and Research Council. If the leak is slow, and the smell emerges gradually, people may not notice the change right away. Other strong smells like tobacco, dampness and food can also mask the scent of propane, the council said. And, the odor can be absorbed into certain substances, including soil, water and rust, making it harder to smell. In rare cases, gas may audibly flow from cracks or holes in the system. Beyond smells and sounds, higher-than-expected usage can indicate a potential leak, according to the propane council. What should I do if I smell gas? If you smell propane, leave the area as soon as possible, Dupuis said. Once at a safe distance, call 911 to report the leak, making sure to tell the dispatcher about any aggravating factors, like if you can hear gas flowing. “Do not light anything, throw a switch, or anything to that point,” he said. “Get outside to make that phone call. Don’t do it inside.” Propane needs a spark to ignite, which can stem from an open flame, a static shock or power leaking from a home’s electrical system. High heat alone is generally insufficient, Dupuis said. While it may be possible to shut off the flow of gas from the main tank, Dupuis recommended residents leave that step to professionals and emergency crews. Many appliances have valves that can be closed directly, “but you’re better off just getting out,” he said. Exactly how far to go depends on factors like the intensity of the leak, the size of the propane system and the makeup of the building, Dupuis said. He also noted that the smell of propane is does not necessarily guarantee a leak. Areas around tanks often smell of propane, Dupuis said, and they smell more strongly after being refilled, since some liquid propane may escape during that process. How can I prevent or mitigate leaks? The Maine Fire Marshal’s Office recommends residents install gas detectors “in any living space where propane or natural gas appliances are used.” Keep in mind that gas monitors are generally separate devices from smoke detectors, though some combination devices exist. Bad weather can also create or worsen gas leaks, according to the propane council. Ice, snow and flooding water can all damage propane systems and block vents, increasing the risk of a gas leak and carbon monoxide buildup. “One thing that a lot of us, all of us probably, fail at: making sure that those lines aren’t cracked, that there’s no rusting around them,” said Scott Doyle, spokesperson for Raymond Fire and Rescue. He recommended checking outdoor lines for potential leaks as temperatures rise in the summer and when they fall in the winter. Propane grills and appliances connected to recreational vehicles tend to be more vulnerable to the elements and may need heightened attention, he said. “You’ve got a whole different level of exposure for propane appliances in a camper or RV,” Doyle said. “They’re jostling up and down the road. You’ve got maybe bigger issues with mice, chipmunks, that kind of thing.” If using a propane grill, Doyle recommended using it at least 10 feet from any structure: keep it off the deck and don’t grill under overhanging eaves. “Propane is very safe. A lot of people get scared of propane,” Dupuis, the Wells fire chief, added. “They need to respect propane, but they shouldn’t be afraid of it.”