What can go wrong and cause an accident in a hot air balloon?

Later this week I am interviewing a member of a local hot air balloon club for a story. It got me thinking - I have never really given much thought to how hot air balloons work. I’ve never been in one; I’ve never seen one up close; all I know about them is that you sit in a wicker basket and that there’s a flame under the bottom of the balloon that creates the hot air to provide lift.

I never hear or read about hot air balloon accidents, though. Is this because they are extremely rare?

What exactly can go wrong on the balloon? Is the simplicity of the system the reason why it is so safe (if indeed it is?) What happens, for instance, if:

You run out of fuel for the heat source?

Something pierces the balloon? (A bird with a sharp beak?)

It suddenly starts raining very hard?

And also - how do you steer the thing?

Is there anyone here who knows the details of operating a balloon and can give an educated opinion on this?

I think the biggest danger is wind. I remember seeing a clip on one of those “Most Amazing Videos” type show where a balloon got blown into a radio tower and tangled up. The occupants had to end up climbing down the tower.

Getting blown into things is a frequent cause of death or injury. Even on flat ground, a high wind will topple the basket when it hits the ground. Running out of fuel means you’ve lost the ability to ascend or to control your descent. Hard landing, or crash with obstacle. There’s always the chance of a leak in the fuel system, resulting in a nasty fire.

As for steering, you don’t. You can go up and down, but otherwise you go where the breeze blows you.

The missing kid blurts out on CNN, “… you said we did it for the show.”

There was a pretty bad accident in Alice Springs ten years ago when one balloon rose into another and ripped.

See here: http://news.google.com/newspapers?nid=860&dat=19890814&id=mDkQAAAAIBAJ&sjid=WY8DAAAAIBAJ&pg=6636,5101833

A gas burner malfunction would be a serious matter.

And by doing so you can catch winds blowing in different directions, which gives you some control over where you are going.

Coincidentally they had that on a TV show, Destroyed in Seconds, here tonight. The host did ask, “Who allowed the balloon to be launched upwind of all those obstacles?” There were a lot of towers it could have hit. Took the father and 2 kids an hour to climb down.

Quite bad, as this eliminates your only means of control. But should also be quite rare, as you’ll be carrying substantially more fuel than you will need for the planned flight.

Very hard for a bird to cause a hole, and small holes would not be a problem. Holes caused by other aircraft and ground-based objects could be serious.

Balloonists are supposed to be sufficiently weather-savvy to avoid such problems. But I have seen a balloon flown in significant rain, and it had no big problems (except for being hard to pack up, and needing to be dried).

As noted above, it simply drifts with the wind. But wind direction may vary with altitude, so a clever pilot can actually do some steering.
The biggest hazard is wind. Powerlines take a toll of careless balloonists.

During launching you can have a failure to communicate which results in the balloon lifting off with one ground helper hanging on a mooring line.

IF that person realizes their error & lets go only a few feet off the ground, they’ll be OK-ish. e.g. a broken leg or two.

If not, they’ll suddenly be hanging on the end of a rope 50 ft in the air & climbing fast. The pilot can’t immediately set down; shutting off the burner will cause the balloon to slowly lose heat and land ~5 minutes later. Even though their life depends on it, most people can’t hold on that long.

Ground crewing a balloon launch takes some skill & everybody knowing the plan. I’ve seen more than one video of people falling to their deaths as I’ve described.

Ex-balloonist here.

Accidents fall into 3 broad categories: launch events, landing events, and propane problems. Often you get a mix of launch or land with propane.

The hands-down most common accident is putting the flame through the side of the envelope while heating up pre-launch. It’s ugly, compromises the envelope strength, and expensive to fix, especially when one of the stay wires gets toasted.

Next most common is hitting something while launching. Utility lines, trees, buildings, etc.

Landing accidents (controlled) are usually a repeat of running in to something.

Propane is the nastiest. Balloons go boom, and considering there are multiple bottles on board, there can be a LOT of boom. Usually, a line is damaged, causing a leak and a fire.

You can also flame out at altitude, but this is rare. Burners are designed with a redundant fire system, so should the primary go out, the secondary can be used immediately. No balloonist I know ever launched without full tanks, BTW.

The next statement applies to the type I flew, which is a top vent. Side vents will vary. If you lost everything at altitude and your vent is properly seated, the envelope will streamer and also act like a parachute. You’ll come down hard, and it’s not pleasant, but the odds are you’ll walk away from the landing.

As far as control, the only axis you can control is vertical. However, winds vary by altitude, so you have some control side to side by playing the wind layers.

No one launches in rain. Balloons are restricted to VFR only conditions, and you can’t get anywhere near a cloud. Also, propane and lightning are a bad mix. FWIW,
winds exceeding 12 MPH meant no launch; landing can be done up to 15 MPH on the ground.

Yeah, power line collisions are the ones that stick in my memory.

Is it possible to accidentally set light to the envelope? If so, that would be pretty catastrophic.

They’re treated with flame retardants, so they will burn through and melt, but not go up a la The Hindenburg. Burn throughs either happen on the ground while heating up, or when the pilot is trying to climb to avoid an obstacle and doesn’t make it. With the limited range of motion on the burner, it’s very tough to burn through in normal flight conditions.

I grew up with the Albuquerque Balloon Fiesta and the vast majority of the fatal accidents have been balloons hitting things while in the air, usually power lines. It seems that this happens every other year or so, but I could be remembering incorrectly. I do know that when they happen someone almost always dies. Last time I was out there for the Fiesta it happened and one or two people died.

Landing accidents can be nasty but, AFAIK, are not usually fatal. I’ve been dragged around by enough balloons* to know that you can get knocked around quite a bit on the landings.

About steering. In Albuquerque they can actually do a bit of steering. Albuquerque has a fairly predictable wind pattern called the Albuquerque Box. in the Box the wind at the lower altitude usually is southern and the upper altitudes it blows north. So by varying your altitude you can pick which way to go.

Slee

*Catching balloons during October was a normal part of growing up. I jumped on a couple balloons every year when I was growing up. They landed all over the freaking place. I only got banged up a couple times when the wind was up a bit. Nothing like getting dragged around by a balloon.

I assume that if you lose your heat source, but the balloon retains its structural integrity and has no leaks, it would then behave like an ordinary toy balloon filled with air, and allow a reasonably soft landing. Presumably, as the descent progresses, the upward pressure on the bag will tend to force the bag into an inverted cone shape, pushing air out the opening in the bottom. So if this happens, is there a way to close off the bottom opening?

One problem is that the rate at which a hot-air balloon loses heat has a lot to do with its vertical velocity. As you descend the balloon cools more, which increases your rate of descent, which increases cooling.

In a terminal descent, you want the bottom open and the top closed. Ramming air up through the bottom creates a parachute effect, but it won’t stay completely inflated; it will become a hybrid parachute/streamer. So long as that air rams into the envelope, you have a good chance of riding it out successfully.

If the upper vent opens, you’re screwed. A complete streamer will most likely be a fatal fall.

Hitting the ground heavily is a major cause of injuries and is pretty common. If you are used to balloons then you can train for the impact, but my Father broke his leg after a hot air balloon ride just because the gondola hit the ground too hard.

Running into power lines gets the balloons at the Albuquerque International Balloon Fiesta a lot.

Obviously heavy winds, or even a light wind can cause you to hit the ground kind of hard, and possibly hit it at an angle which might cause the gondola to topple and throw you out.

Basically a hot air balloon is a big bladder with a vent at the top of it. You fill it with heat from the bottom and you can release the heat at the top by pulling on the flap with ropes that hang down inside of it.

sleestak I thought the Albuquerque Box actually went in all four directions at different altitudes.

EDIT: Looking at Wiki, I see I was wrong.