Hydrogen and helium are the lightest elements in the periodic table. They exist as gases at room temperature and are the two most common elements in the universe, with hydrogen making up about 75% of all matter.
On Earth, hydrogen mostly exists in molecules such as those of water, minerals in the earth and organic compounds. Most of the helium on earth is emitted from radioactive elements underground. Both elements exist in very low quantities in the atmosphere.
Hydrogen was first identified as an element in the 1700s, but had been produced since the 1500s by simple reactions of acid and metal.
Hydrogen gets its name from the Greek words for hydro and genes (water former), because it produces water on burning.
Hydrogen is the odd one out in the periodic table. It is a gas – the same as helium – but can act in a similar way to the alkali metals. It likes to form covalent and ionic bonds, which is also unusual. It is prevalent in organic materials.
Hydrogen is most often positioned above the alkali metals in the periodic table although its properties are only superficially similar.
Hydrogen has a molecular weight of 1 and is lighter than air (the main component of air is nitrogen, which has a molecular weight of 28).
Helium was identified in several ways. In the 1800s, various scientists first observed it in the spectrum of light from the Sun and then in the spectrum of gases being emitted from Mount Vesuvius in Italy. Helium was also identified when an ore of uranium was dissolved in acid.
Hydrogen was originally used to fill balloons and airships. However, it was replaced by helium following the Hindenburg disaster in 1937. It is also used in many different chemical processes as a reactant. Hydrogen has a lot of potential as a fuel – by burning the gas and using hydrogen fuel cells to generate electricity. Hydrogen fuel cells are already being used in public transport to power buses (e.g. Aberdeen has six hydrogen fuel cell buses operating on its routes).
Because helium is very unreactive, it is sometimes used to create an inert atmosphere to carry out delicate or hazardous processes. It is also non-toxic so is used by divers as a safer
Helium is named after the Greek Sun God, Helios, because it was in the Sun’s corona that it was first detected.
Helium has a molecular weight of 4 and, like hydrogen is lighter than air. While helium is not as light as hydrogen, it is inert and non-flammable (unlike hydrogen, which is highly flammable). For this reason, helium is used to inflate party and meteorological balloons as they will rise in air.
alternative to nitrogen at more extreme depths. Liquid helium is extremely cold (-2700C), so it is used as a coolant for magnetic resonance imaging (MRI) scanners, instruments in satellites and other delicate instruments.
Hydrogen and helium have different hazards, but similar chemical properties. As both are gases, ventilating an enclosed space where they have been released is essential before people are allowed to enter, unless they are wearing appropriate protective equipment. As both gases are lighter than air, it is important to remember that they will accumulate towards the top of any space into which they are released. While hydrogen is non-toxic, it is highly flammable, so a release of this gas in an enclosed space has the potential to create an explosive atmosphere. Therefore, it is important to ensure there are no ignition sources in the area.
Some of the calls NCEC receives concerning helium are about people who have deliberately inhaled the gas to achieve the ‘squeaky voice’ effect. However, inhaling too much helium can cause loss of consciousness as it limits the amount of oxygen in the lungs. Inhaling helium may cause these effects without warning or they may first present themselves as a feeling of light headedness or dizziness. Inhaling helium from a high-pressure source, such as a cylinder, can also cause physical damage to the lungs due to the force with which it leaves the cylinder.
Hydrogen can be released from chemical reactions. Consequently, it can be an issue in incidents where it was not the gas initially released. NCEC often receives calls that are related to acid spills. Our typical advice is that hydrogen is given off when the acid reacts with metals. It would appear as bubbles being given off where the acid and metal are in contact. Fumes might also be visible depending on the conditions. The amount of hydrogen given off depends on the strength of the acid and the reactivity of the metal.
In one incident, NCEC was contacted about a fire that potentially involved containers of liquid helium and liquid nitrogen. Our emergency responder was able to advise that the liquified gases would displace air and pose an asphyxiant risk if released from their containers but could also help with extinguishing the fire in the same way that carbon dioxide does (i.e. by starving the fire of oxygen). The caller was advised to cool the containers to prevent pressure building up inside, avoiding the risk of the container rupturing. It later transpired that the liquified gases were not involved in the fire, but the advice had helped to minimise the risk to the fire and rescue service crew involved with the incident.
Lithium, Sodium & Potassium
Next month’s issue will focus on the alkali metals, which include lithium, sodium and potassium. These elements are fundamental to our lives – from a biological point of view and the technological advancement in our daily lives. These are also some of the most reactive elements and we will discuss how this impacts NCEC’s emergency response advice.