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Airships are much safer than aeroplanes

What did you say?
I said “Airships are much safer than aeroplanes.”
That’s what I thought you said.
Don’t be daft. Everyone knows people stopped building airships because they were so dangerous.
I beg your pardon?
Well, they were always crashing in flames and killing all the passengers.
OK - name two airships which crashed like this.
Easy. The Hindenburg.
And the second?

Actually there isn’t even one. When the Hindenburg crashed in flames on 6th May 1937 only thirteen of the thirty six passengers and twenty three of the sixty one crew were killed. The World's first airship was built in 1852, by a French engineer called Henri Giffard. More than a hundred and fifty years later there has only been one airship accident involving the death of a passenger - and that was the Hindenburg.

During the 1920s and 1930s there were three very highly publicised accidents involving airships: the American Shenandoah, the British R101 and the German Hindenburg. However, only the Hindenburg involved the death of a passenger, not one of these accidents was caused by a hydrogen fire; all of them were the direct result of political interference. The accidents to the Shenandoah, R101 and Hindenburg were and still are very much the exception: all the published accident statistics show that airships are now and have always been much safer than aeroplanes.
OK, OK - so helium is safer than hydrogen. But the airship will still crash if the envelope bursts: think of a party balloon.
Actually, don’t think of a party balloon - an airship is not a bit like a party balloon.

Take a party balloon and stick a pin in it. There will be a loud bang and the balloon will disappear. If you pick up the pieces you will find it has been torn in half. Now stick a piece of Sellotape® or similar on the balloon and stick the pin through that. The Sellotape will stop the balloon from tearing and it will just deflate quite slowly. Every airship that has ever been built has been made of a rip-stop material.

Party balloons are made of a very stretchy material. As you blow up the balloon it stretches, and this needs a force which comes from the pressure inside the balloon. The bigger you make the balloon the more it stretches and so the higher the pressure must be inside it. If you blow the balloon up too much it will burst.

The envelope of an airship is made of a non-stretchy material, and the pressure is only just above atmospheric pressure. There are two reasons why we need to keep the pressure inside the envelope very low.

Most people do not realise how very low the pressure of the helium inside an airship is: it is actually only about 50 mm of water.

Take a see-through drinking straw and make a mark on it about 5 cm from the bottom, then another mark 5 cm above that. Put the straw into a glass of water until the top mark is level with the surface. Keeping it as nearly vertical as you can blow very gently into the straw until the water level in the straw reaches the bottom mark.

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This is a pressure of 50 mm of water, about the pressure of the helium in an airship!

Plastic bags are dangerous, so younger children should not try this next experiment except under the supervision of an adult.

Take a pedal bin liner, the larger the better. Wave it around to make certain the sides are not sticking together, and then pull it through the air to make it inflate. You can also use a hair drier to inflate it, but do not try to blow it up by putting it near your mouth. Close up the end and seal it with a rubber band. You may need to slide the rubber band along the neck to make the volume of the air in the bag smaller until it is quite tight.

Now stick a pin into the bag and watch what happens.

The pressure inside the envelope of an airship is so low, and the volume of helium inside it so great (more than 1000 m³ of helium per tonne of buoyancy) that even if there is a hole, or even several holes, in the envelope the helium will only leak out very slowly. In 1994 the British Ministry of Defence carried out some tests on a non-rigid airship. These tests included firing several hundred bullets into the envelope. It came down to Earth of course - more than five hours later!

A party balloon is made of a type of rubber which is slightly porous, so the air will leak out of it over a few hours or days. But airships, even the toy foil helium balloons you can buy in shops, are made of a non-porous material. In 1984 I was teaching at a school in London. I had to go into hospital and one of the children in my class gave me a Get Well Soon helium balloon. More than twenty years later it is still fully inflated! If you stop to think about the envelope of an airship and the hull of a ship, and how they are made, you will realise that it is probably a lot easier to make an airship which does not let out helium than a ship which does not let in water.

If all the engines on an airship stop working at the same time the airship will still stay in the air, it will just not be able to move. Then the pilot, or even a passenger if all the crew have been taken ill, can let the helium out very slowly, and by the time it has reached the surface, of the land or of the sea, say five hours later, all the rescue teams will be there waiting for it. The same is true for any other systems failure. No disaster movies here!

An airship carries much less fuel than an aeroplane, and travels much more slowly, so an airship is much less likely than an aeroplane to fly into something like a mountain, but even if one were to do so there is much less chance of it catching fire, and the passengers are much less likely to be killed or badly injured.

Airships were used in two World Wars and have been and are still being used in other War Zones with great success and with a very good safety record: this is discussed in the Pages on 20th and 21st century airships.

© Barry Gray January 2006