Airships - helium or hydrogen?

Helium

Helium was first discovered in the sun in 1868 by French astronomer Pierre Janssen. He thought it was Sodium. Later that same year, Norman Lockyer observed it and realised this was a completely new element unknown on earth. It was almost 27 years when it was finally discovered on Earth.

Helium is colourless, odourless, tasteless, non-toxic gas. It is found in vast quantities beneath the Great Plains (in America).

Until the 1990s America produced 90% of the world's helium, with the rest coming from Canada, Poland, Russia and a tiny amount from a few other nations.

Hydrogen is more bouyant than helium, but helium has the benefit of being both non-flammable and flame-retardant. This is why it is commonly used in airships.

Breathing pure helium continuously causes death within minutes by asphyxiation.

Hydrogen

75% of the universe is hydrogen. There is very little of it in its elemental form on earth. Most of it is extracted from hydrocarbons. It is highly flammable. It will spontaneously combust at 560 °C. Pure hydrogen-oxygen (between 4 and 75% hydrogen) flames emit ultraviolet light and are almost invisible to the naked eye.

When the Hindenberg famously exploded, the flames that were seen were from the combustible materials that made the ship.

Jacques Charles invented the first hydrogen filled balloon in 1783.

It is 7% more bouyant than helium.

As a rule of thumb, 1 cubic meter of hydrogen lifts 1.1 kilogram, 1 m3 of helium lifts 1 kg and 1 m3 of hot air lifts 300 grams. (In Anglo-American measures: 1000 cu. ft. of hot air lift a maximum of 20 lbs. and 1000 cu ft. of helium lift about 60 lb.) These figures are on the safe side and allow for variations in altitude, temperature, humidity and also purity of the helium.

This quote comes from a handy little site, here http://www.myairship.com/faq/index.html. Steampunk World recommends it, and that's all the recommendations you need, right?

Anyway, hope this helps...