Hydrogen looks promising as a plentiful alternative to fossil fuels, but the risks of electrical shock and flammability must be managed first, writes Michael Edwards GradIOSH.
There has been talk for years about how the world can move away from fossil fuels towards environmentally friendly alternatives. As well as power generation, the automotive industry has been developing other ways of propulsion. While the main low- or zero-emission vehicles sold today are lithium-ion battery electric vehicles, hydrogen fuel cell vehicles are a viable alternative.
Hydrogen-powered fuel cells convert the chemical energy in the stored gas to electrical energy via an electrochemical process. This creates electricity to power the vehicle.
This process is extremely efficient. Nine litres of water can produce one kilogram of hydrogen via electrolysis. One kilogram of hydrogen contains 33 kilowatts of energy, which translates to a range of around 100 kilometres.
Hydrogen used in fuel cells has an energy to weight ratio 10 times greater than lithium-ion batteries. Consequently, it offers much greater range while being lighter and occupying smaller volumes. It can also be recharged in a few minutes, much the same as refuelling gasoline vehicles. However, hydrogen fuel cells have disadvantages compared with their battery-powered cousins: the availability of refuelling stations (in the UK, there are just 11); the cost of refuelling of between £10 and £15 per kg; and potentially less efficiency than batteries, from source of generation to fuelling the vehicle.
But are hydrogen-powered vehicles safe?
The two main hazards from fuel cell and hydrogen-powered vehicles are electrical shock and fuel flammability.
Fuel cells power vehicles by electrochemically combining hydrogen gas (H2) and oxygen (O2) from the surrounding air into water (H20) and electrical energy. The electrical energy is then used to power both the locomotion of the vehicle through electrical motors and the current electrical usage devices such as the radio, lights and air-conditioning.
Some fuel cell vehicle motors run on voltages exceeding 350V. With such high currents, the danger of electric shock is great, with 50V being high enough to stop the human heart.
The flammability of hydrogen is also an issue. Hydrogen has a flammability range between 4% to 75% in air, which is very wide compared with other fuels (gasoline is to 7.6%). Under the optimal combustion condition (a 29% hydrogen-to-air volume ratio), the energy required to initiate hydrogen combustion is much lower than that required for other common fuels (for example, a small spark will ignite it). However, hydrogen is about 57 times lighter than gasoline vapour and 14 times lighter than air. This means that if it is released in an open environment, it will typically rise and disperse rapidly. This is a safety advantage in an outside environment. Hydrogen also burns with an almost invisible flame, making it less noticeable and harder to firefight.
So leakage of hydrogen can be a concern, especially when vehicles are stored in enclosed spaces as hydrogen can build up in roof spaces. Due to its small molecular size, hydrogen disperses quickly at normal atmospheric pressure. Therefore it needs to be maintained at higher pressures (up to 10,000 pounds of force per square inch). The rupture of a pressure tank can cause high concentrations of hydrogen to form in the vicinity of the vehicle, as the turbulent flow rate of hydrogen is extremely high. Even though hydrogen disperses quickly, this emission will cause a combustible mix to form for a short period in the open.
But do these hazards pose a risk to drivers and maintenance operatives?
No hazard ever exists in a vacuum. All vehicles must be manufactured to minimum safety requirements, either nationally or internationally.
The United Nations World Forum for Harmonization of Vehicle Regulations sets safety standards for motor vehicles. Standards for electrical safety, such as IEC 60664-1:2020 Insulation coordination for equipment within low-voltage supply systems – Part 1: Principles, requirements and tests, and ISO 19881:2018 Gaseous hydrogen – Land vehicle fuel containers, give minimum requirements for design specifications of components for electrical and fire safety.
H2Tools.org produced a paper based on the safety of hydrogen fuel cell cars.1 Researchers tested the electrical safety measures and leakage of hydrogen, both in use and post-crash. The electrical isolation and electrical continuity met the requirements in use and post-crash and no leakages from the tank were identified.
Maintenance of hydrogen fuel cell vehicles is a niche profession. Operatives will need to be aware of not only the requirements of the design of fuel cells, but also of the risks of defeating protective features to adequately maintain the vehicle.
So what does this mean for us as OSH professionals?
While we might be unlikely to deal with hydrogen-powered transport that much in our current work environment, it is possible that hydrogen fuel cells will be more available and more used in the future. We should be aware of any developments in technology related to hydrogen fuel cell use in our horizon-scanning activities and how we can control risks that emerge.
What do you think about the risks posed by hydrogen fuel cell vehicles? Tell us in the comments below.
1. Pacific Northwest National Laboratory Hydrogen Tools Portal (2011). Assessment of safety for hydrogen fuel cell vehicle. See: https://h2tools.org/sites/default/files/2019-08/paper_56.pdf (accessed 21 May 2021).