In the worst hot air balloon accident in at least 20 years, 19 tourists died in a hot air balloon explosion in Egypt on Tuesday.
While there are conflicting reports of how the accident happened, a look at safety regulations and past accidents provide a glimpse into the risks of the oldest form of human flight.
"A balloon is a very simple thing," said Glen Moyer, editor of Ballooning Magazine, the Journal of The Balloon Federation of America. "You've got the protection of the wicker basket and a little rubber padding. It's generally very safe, but when something bad happens there are not a lot of options."
The primary dangers, he said, are hitting power lines and hard landings.
The balloon's operating company said a gas cylinder exploded on board, according to the BBC. But it's unclear what caused it to explode.
Some element of pilot error usually plays into an accident, such as not seeing a power line, Moyer said.
Fires are not common, but often lead to explosions because of the close access to propane. A fire would almost certainly be caused by a mechanical failure, Moyer said, such as a leak in a hose or a loose valve connection. Then any sort of spark, even from a nylon jacket, could cause a fire and explosion, he said. The only escape at that point is jumping to the ground, as the pilot and one passenger apparently did in the Egypt explosion.