Natural gas, or "street gas" is 99% pure Methane, CH4, which has a molecular weight of 16, compared to that of air, which is about 28, so it's also a "lifting gas" and has been used as such in a pinch. But it's still a lot heavier than H2 (MW=2) and He (MW=4). The "lifting power" of a balloon gas is determined by the >difference< in MW's of the gas and air. So even though
H2 has half the MW of He, in air, it's only got about 8% more lift for a given volume.
It's also worthy to note that a H2-air flame is nearly invisible - a very pale blue which, unlike carbon based flames, emits negligible infrared radiation. The flames seen in the HIndenburg newsreel were thus obviously not H2 flames. It turns out that the fabric that formed the skin of the airship contained highly flammable additives,
which burned with bright yellow flames. Of course, once the airship's structure failed, the H2 in the cells was released, mixed with O2 in the air and added more fuel to the fire.
In the US, the National Weather Service launched some 120 weather balloons daily from sites across the continent, and for several years now, all of them use H2 vice He due to the latter's
soaring cost. The primary added precautions are avoidance of H2 leaks and accumulation in buildings and avoidance of ignition sources such as static discharges and other electrical arcs, and the like. H2-air mixtures less than 4% and over 75% H2 concentration, as would be
the case in a balloon, are not flammable.
Nonetheless, it's easy to gripped by "Hindenburg Paranoia", as apparently have the LOHAN guys.
Mike Manes W5VSI, CTO EOSS