The color in a natural gas flame is carbon. Natural gas is a mixture of hydrocarbons, primarily methane (CH4) but with variable (typically < 3%) levels of CO2, Nitrogen and whatever else they can stuff in while keeping the SG (specific gravity or density) inside a specification range as well as maintaining a heating value of about 1000 to 1050 Btu/scf. Additionally there is a Wobbe index spec that standardizes the fuel energy flowrate through a fixed orifice under standard conditions.
The smell in natural gas is a sulfur compound, (H2S, hydrogen sulfide is the rotten egg smell) Ethyl Mercaptan (Ethanethiol, C2H6S) is the typical odorant in Nat Gas. Sulfur compounds are found naturally in rotten eggs, onions, garlic, skunks, and, of course, bad breath.
Hydrogen is colorless and odorless and burns with an almost invisible flame Although hydrogen burns in air over a wide (4% to 75% ) range of mixtures with air, a small leak disperses rapidly and is surprisingly hard to ignite (particularly a small high velocity leak from a high pressure source) considering hydrogen’s very low ignition energy. A big potential problem is letting hydrogen gas collect at the top of an enclosure, and hydrogen detectors are used for most indoor industrial applications. With the advent of hydrogen fuel cell vehicles, low cost hydrogen detectors are being developed that will be positioned all over the vehicles to monitor leaks. Infrared or UV cameras or sensors can be used to detect hot (ignited) leaks.
Adding colorants or odorants is very problematic as the most valuable use for hydrogen may be with Fuel Cells and any CO or sulfur compounds will poison the platinum used in the Fuel Cell. The DOE is spending quite a bit of coin on Hydrogen right now and some of that is to find an acceptable odorant. So far, not much progress, and I am not too sure a good odorant for hydrogen will be found. (go ahead and please prove me wrong)
If you have a continuously venting hydrogen stream, add a twisted nickel-chrome wire to the vent stack and ignite the leak, The nichrome wire will glow a nice bright red-orange and if the flame gets blown out, the hot wire will re-ignite the venting hydrogen. For intermittent venting, I would suggest a pilot flame with a UV, IR or thermal sensor.
Approaching a suspected hydrogen leak with a straw broom or a loosely rolled up newspaper is an industry approved standard method of practical flame detection. Do not try to extinguish a hydrogen flame except by shutting off the source.
