My question concerns the construction of balloons. Would the gas (whatever it be) contribute to the fire, which seems to have started in the basket? Would the fire spread too rapidly to have any hope of extinguishing it? Is there any way to descend the balloon quickly in an emergency, other than crashing? How high do these balloons fly and would fire burn more quickly at a great height? What would the safety procedures be in the event of fire?
The ‘gas’ is just hot air. The balloon lifts only because hot air rises, as opposed to a Zeppelin/Blimp/Lighter Than Air vehicle that’s filled with something that floats like, I don’t know, hydrogen.
I didn’t look at your link yet, but I’m guessing once the balloon is on fire, you’re really in trouble. I’d think/hope they’d make it out of fire retardant materials, but, really, it can only have a hole so big in it before it’s going to lose altitude at an unsurvivable rate. And, of course, if the basket and/or ropes go, the passengers are going to fall.
I posted earlier on this but it seems to have gone unnoticed. 
Photos of the scene show a major power line running right through the middle of the area. There’s still no details except the four or five they keep repeating. As I said, I don’t think balloons can carry 16 adults… there are almost certainly children in the casualties.
I didn’t realize that there were hot air balloons capable of carrying that many passengers.
I think aldiboronti knows that. I could be wrong, but in reference to the fire starting in the basket, I took the question to be asking about the fuel for the burner, which might be propane or some other gas? I don’t what hot air balloons generally use for fuel.
Some can. We tend to think of gondola baskets as being a few feet square and accommodating Phileas Fogg plus a couple of his companions, but some of the modern ones that are constructed for balloon experience flights are the size of a minibus
ETA- Example: http://i.usatoday.net/communitymanager/_photos/dispatches/2011/12/26/Orlando%20Balloon%20Ridesx-large.jpg
I’ve been at launches of balloons with up to 6 people on board, and it looked like the gas tanks were in the basket with the passengers. It always seemed like it needed a full propane canister per person, but I was 20-30 feet away.
The internet indicates the gas fuel is propane.
I never saw one that held 20 people, but the smaller baskets only had about 8x8 feet of room in the basket.
At several hundred feet up, if one of those tanks leaked and started to burn / broil passengers, it seems like the passengers could either stand there and be burned… or jump. 
2013 Luxor hot air balloon crash
On 26 February 2013, at 07:00 Egypt Standard Time (05:00 UTC), a hot air balloon crashed near Luxor, Egypt. The crash resulted in 19 deaths out of 21 passengers – 18 on-site and one in hospital hours later.[2][3] It was the deadliest ballooning disaster in history, surpassing the Alice Springs hot air balloon crash in 1989 which killed 13 people, and the deadliest aerostat disaster since the USS Akron crash in 1933 which killed 73 people.[4][5]
Hot air rises because it’s less dense than cooler air. So a hot air balloon operates on much the same principles as a helium or hydrogen balloon.
It’s nearly always propane.
I frequently crew for a commercial hot air balloon pilot. He recently purchased a system that holds 16 people or so. The envelope itself holds 250,000 cf of air (I haven’t crewed this system yet.) But he also has systems as small as 70,000 cf for private flights.
The envelopes themselves are made up of several different materials. The main part is made of rip-stop nylon. The top is (I believe) a heat resistant nylon, and the scoop and throat (the parts closest to the burners) are made of Nomex, a fire-resistant material that is also used in firefighter gear.
The burners use propane as a fuel. The number and size of tanks varies. The 70,000 cf system has 3 15 gallon tanks.
Huh. This crash killed more passengers than the Hindenburg (the Hindenburg crash killed 35 people, but 22 were crew and only 13 were passengers).
Maybe not. There is speculation that two passengers missed the flight and there would have been at least one crew.
BTW, “crew” in this context means unloading the balloon, setting it up for flight, driving the chase vehicle, and packing up everything post-flight. There’s no in-flight service. 
While it might not have helped in this particular case, I have always wondered why there never seems to be any flame arrester surrounding the burners in balloons. Something like in the Davy lamp; just a thin mesh of wire. And it could easily be made retractable; folding together like the bellows of an accordion, so it needn’t take up space when not in use.
Open flame and flammable fabric just seems to me like a really bad combination!
The part of the envelope near the flame (the “mouth” or “throat”) is made of Nomex, a flame resistant material also used to make firefighter gear.
I doubt the balloon was set on fire at altitude by the propane tanks. I think the fire was more a result of the balloon gondola running into high voltage transmission lines (the wreckage is reported to be right underneath a main line) as the pilot tried to stay under the overcast. I would imagine propane tanks bouncing around unshielded electric lines is not a very good mix.
Looked up the weather for Maxwell, TX. The closest reporting station is San Marcos Airport which is about 10 miles away. At 7:47am CT (the crash occurred at 7:40am), San Marcos was reporting light winds, 2 miles visibility in fog/mist, and overcast skies with a ceiling of just 300ft.
If I am reading the sectional map right, the minimum safe altitude is 1400ft. If the balloonist was trying to stay out of the clouds, he didn’t have much room for error if he suddenly come across something sticking up a little bit higher than expected.
I’d like to know where exactly he launched from, the weather there, and what the weather briefing and forecast was. San Marcos weather had been clear just 90 minutes before the crash, I wonder if they launched in good weather and the weather closed in unexpectedly.
The likeliest cause of fire in a hot-air balloon is a propane leak, ignited by the main burners. The unenviable choice is between burning and jumping.
I once had a factory next door to Thunder Balloons http://www.ballooninghistory.com/thunder/ headquarters. One day nobody came in to work. And they never came in again.
It was a tragic business; I understand it was due to a propane fire as above.
As more information comes in some have reported that the balloon hit the power lines. What happens in cases like that is the huge electric arcing from the short-circuited high-power lines will ignite almost anything in or on the balloon that touches them, and eventually the propane gas system starts leaking and ignites. I’ve seen at least one video (of a different, past incident) where power lines actually made contact with a propane tank itself and it exploded immediately.
The material that makes up the balloon itself is fairly flame retardant (I assume it’s some kind of rip-stop nylon) but once you have a propane-fired inferno burning directly underneath it (heat rises) nothing can stop the material from simply melting and disintegrating. As this happens (rather quickly) the hot air begins to escape, and the balloon rapidly loses lift (i.e. buoyancy) and starts falling faster & faster. I’ve also seen another older video where a fire destroyed (again melted) the ropes that attach the gondola to the airbag, which then immediately plummeted to the ground.
Too early to say for sure exactly what happened, but the power lines being so close to the crash site make them a definite possibility.
Power lines and hot air balloons don’t get along well. About 30 years ago a friend of mine and his siblings gave their parents a hot air balloon ride for their anniversary. During the descent, the balloon grazed a power line causing it to fall. They were low enough that they all survived with just bruises and scrapes.