The following information is reprinted with permission from  Gone with the Wind - Manual for Gas Ballooning by Walter Muller, Astrid Gerhardt and Gerhard Hurck.  Copyright September 2002

6.0. Hazards and safety when using hydrogen

6.1 Hydrogen

6.2 Characteristic values

6.3 Hazard properties

6.4 Hints for practical use

6.5 Brief information on static electricity. Electrostatic charging and the danger of discharge

6.1 Hydrogen*

Of all gases qualifying as lifting gas meaning lighter than air", hydrogen has the lowest density and the highest availability. Considered aerostatically it is the filling gas of the highest grade, with its help some significant scientific findings concerning the atmosphere could be brought about in gas balloons and some remarkable sportive balloon flights were made possible.

Table of data

Standard density (0° C) = 0.09 kg/m3
Mass-related volume = 11 m3/kg
Relative density (air = 1) = 0.07
Density ratio (H2 - air) = 1:14
Lifting capacity = 1.2 kg/m3

Hydrogen was first discovered as combustible air" in the 18th century  (1766, Cavendish U.K.). It then received its name as chemical element hydrogen" (trsl. From Greek: to create water) and has been known since as hydrogen. In 1783 it was first used as a balloon filling gas for the ascent of the first gas balloon (Charliere), just a few weeks  after the first flight of a manned hot air balloon (Montgolfiere). Hydrogen, the most abundant element in the universe, has the simplest and lightest atom (1electron revolves around 1proton). In an unbound state it forms two-atom molecules described by the formula of H,.

In industry hydrogen is in use in manifold fields of production, e.g. as an element/partner in chemical reactions, or as a fuel produced through the burning with oxygen.

The production of hydrogen is effected mainly through a chlorine-alkali-electrolysis or through catalytic separation of methane or hydrocarbons. Compared with conventional helium, hydrogen has a very high purity of more than 99 %.

6.2 Characteristic values

Hydrogen is a flavorless, colorless and combustible gas. It is highly inflammable, and highly explosive when mixed with air (oxygen). These characteristics, which will be treated in detail in the sections to follow, point to the specific dangers of the gas. Such dangers have to be born in mind when using hydrogen in balloon sports. Important safety characteristics:

Ignition temperature = 560° C

Ignition energy = 0.02 mJ (mWs) (1)

Ignition limits =4 - 76 vol.% (2)

Flame temperature = 23000 C 1:2)

Combustion speed = 2.65 m/s (3)

Detonation limits = 10 - 65 vol.%

Detonation speed = 1.5 - 2.2 km/s

Energy of explosion= 2 kg TNT/m3 H2

(1) 20 degrees C Normal pressure

(2) in air

(3) Maximum value at 45 vol % H2

6.3 Hazard properties

 

H2, is colorless and odorless.

  • Escaping gas cannot be seen or smelled

  •  Escaping gas can displace breathing air and there is danger of suffocation.

  •   H2 burns with a colorless flame.

  •   A fire with H, involved is difficult to discern at the beginning.

H2, is highly inflammable.

  •  It has by far the lowest ignition energy of all gases. Due to its high inflammability few sparks caused by an electrostatic discharge, yet even a silent discharge in the vicinity of a thunderstorm (Corona effect), are sufficient to cause an ignition.*
  • The danger of an ignition through electrostatic charge increases with a high flow-out speed (relaxation) and when the gas is polluted by rust or dust particles.
  • Danger of an ignition through the energy of a static charge as it occurs while wearing clothes made of synthetic fiber or shoes that are not conductive.

H2 without the addition of air during free flow-out quickly volatilizes upwards.  (about 60 m/s). No explosive gas mixtures are formed. After just a short period.  After just a short period the value will fall below the inflammability limit again.

H2 has a high flame temperature but a low heat radiation.

  •  Due to its far higher flame speed when compared with other combustible gases (lighting gas, methane, propane, etc.) on the one hand, and due to its lowest heat energy per volume unit on the other hand, H, in the open and when not mixed with air will burn quickly (deflagration), without pressure, and in the form of a high darting flame. The heat radiation of the flame is relatively low. Despite the high flame temperature the surrounding area is not in much danger. (Deflagration of the airship .Hindenburg" in 1937 in Lakehurst)

H2 is explosive in mixture with air oxygen

 

  •  Due to the very large explosive ignition range even small amounts of H2 can lead to explosive gas-air-mixtures. Fast deflagration inside the envelope may turn into a detonation causing the destruction of the envelope. Due to the fast deflagration, however, no high pressure can be generated The mechanical effect of the explosion's pressure towards the outside is small.

H2 may ignite during pressure release

  •  There is always a risk of self-ignition in case of broken inflation tubes and sudden pressure release due to the heating of  the gas." The ignition risk rises with increasing dryness of the air. Numerous deflagrations and explosions in the history of balloon sports,-be it during inflation, during the flight with a storm front approaching or during deflation after landing-account for the high inflammability of combustible filling gases.  By improving the conductivity of the whole system (fabric and lines) according to building regulations and to special prescriptions concerning inflation and deflation to reduce, the dangers could be reduced to a tolerable level.  When the following hints and rules are being taken into account for the use of hydrogen, safety can be guaranteed to one’s best judgment.

The responsibility is exclusively in the hands of the pilot

  • Does the balloon have permission for combustible gases

  • Are all parts of the balloon connected in such a manner that they are conductive?

  • Have all possible ignition sources been removed?

  •  Also mind the corresponding instruction in the flight manual.

6.4 Hints for practical use.

The following hints refer to filling from pipes, stationary gas tanks or gas tank trucks.  Requirements and terms as listed in the official admission documents for gas balloon launch sites including the corresponding rules and  regulations, remain unaffected and ought to be given priority.  The required safety instructions can be derived from the hazard properties of hydrogen.

The inflation instructions listed in chapter 5 are also valid and have to be followed:

Balloon

The gas balloon must have permission for the use of hydrogen (flight manual).

Protection Zone / Inflation area

The protection zone has to be cordoned off, visible signs, which indicate that smoking is prohibited, have to be placed.  All possible ignition sources have to be excluded.  Persons that are not authorized have to be kept away from the inflation place.  The same is true for moving or standing motor vehicles.

Inflation

Pilot, balloon master, and inflation aides have to be informed about the hazards and safety instructions when using hydrogen.  They must be familiar with the local conditions.  The inflation personnel must wear clothes and shoes that are antistatic.

Inflations tubes.

The inflation tubes must be conductive and leak-proof.  The main closing valve always hast to be staffed.  The person in charge has to be in visual contract with the pilot or balloon master all of the time.  Two fire extinguishers (powder) with a minimum content of 12 kg has to be within reach.

Explosion Protection

Minimum safety distances

-          10 meters between inflation socket and protection zone.

-          6 meters around the balloon.  Only explosion safe lamps and tools may be used.

Launch

When there is evidence of an approaching thunderstorm the inflation process must be immediately stopped.  If necessary the envelope can be deflated with the help of the quick deflation system (parachute).  Starting is prohibited when there is a storm front approaching.

Flight

When the risk of a thunderstorm becomes manifest during the flight or a thunderstorm is already in full swing, immediately landing is inevitable. 

Deflation

Be cautious while deflating: friction and motion of the envelope can lead to electrostatic charge.  For deflation the same rules apply as for inflation concerning the distances, the clothing and ignition sources.

Action in case of gas fires

If possible, extinguish the flame by immediately closing the gas supply line.  If this is not possible, leave the gas fire burning until the fire fighters arrive, because there is always a risk of re-ignition after the flame has been extinguished.

Balloons that are filled with H2 burn without pressure and with a high darting flame.  Remains of the burning envelope falling down can be a potential threat to people standing nearby.  Special caution is required in cast of the burning of the balloon envelope that is filled with as and air.  Deflagration can suddenly turn into a teonation with a pressure and heat effect.

 

6.5 Brief information on static electricity, electrostatic charging, and the danger of discharge

1.  Electricity can be current or static:-Current electricity = Electric current – motion of electric charges by means of conductors in an electrical circuit – Static Electricity = static electricity – charging with varying charges (+/-)

2.  Static electricity becomes dangerous when different charges balance each other.  This results in a flashover or a lightning.

3.  The danger of an ignition through and electrostatic charge depends on the ignition power.  The ignition power for combustible gases, especially for hydrogen is very low.

4.  Electrostatic charges are among others the result of the mechanical friction of solid surfaces.

5.  One of the preconditions for an electric charge are varying electric resistances of different materials.  The higher the resistance of the material the more charge carriers will carry.

6.  Streaming pure gases are not receptive to charging.  The only substances that are receptive to charging are the pollutions in the gas and materials where the gas flows by.

7.  An electrostatic charge can be discharged by electric conductors.

 

Footnotes:

 

"The combustible and explosive filling gas hydrogen nowadays is the gas that is most commonly used as a filling gas for balloons One exception to this fact is the incombustible filling gas helium, winch is most commonly used in the country of production USA Such combustible and explosive gases like hydrocarbon gases, which had been in use far into the past century, lighting gas to name but one. are not a matter of discussion in the chapters to follow They are characterized by early the same hazard properties as hydrogen. The authors therefore refer to the common writings.

*See appendix containing brief information on static electricity  

** A specific characteristic of hydrogen is the heating of the gas in case of pressure release (negative Joule- Thomson effect). When pipes or tubes that are under high pressure burst there is always a risk of self-ignition of the escaping gas.