So how dangerous is hydrogen as a fuel?
In many situations where a vehicle is located outdoors, hydrogen is safer than conventional liquid fuels or natural gas. This in no way implies that hydrogen is not dangerous — there are many situations where hydrogen, like any other fuel or energy storage device, can cause an accident. As one life-long hydrogen expert said to me once, “Hydrogen is no better, nor worse, than any other fuel. You just have to know the rules for working with hydrogen.” – quote from Jacob Leachman discussing hydrogen safety.
Hydrogen safety is paramount in our engineering for applications.
Hydrogen safety – physical properties
The three rules of hydrogen:- ventilation, ventilation and ventilation
Hydrogen’s physical property of buoyancy means that, if not confined, it will disperse into the atmosphere. So ventilation is the primary safety measure to prevent accumulation to a flammable level.
It’s very lean flammability limit and low energy density means that there is little contained energy in a flammable mixture.
It’s low radiated heat means that consequential damage from a flame is smaller than damage created by the flame of other gases.
Hydrogen safety – use international standards
There are already mature standards used throughout the world for hydrogen.
For the automotive sector, the EC79/2009 standard governs application of hydrogen as a fuel to road vehicles.
The ADR regulations cover carriage of dangerous goods including compressed and flammable gas like hydrogen.
The IGF code covers all areas that need special consideration for the usage of the gas or low-flashpoint liquids as fuel.
Hydrogen safety – CMBs three layers of safety
Hydrogen safety layer one:- physical components
CMB have developed the three layers of safety methodology for hydrogen systems engineering.
The physical components – tanks, valves, thermal pressure relief and excess flow devices all form the first layer of safety.
The tanks undergo extensive testing (including a bonfire test, an armour-piercing bullet test, a drop test, corrosion and impact tests) to ensure they are as safe as possible. Tanks from each batch manufactured must survive this suite of tests to conform to the EC79/2009 standard.
The tanks are fitted with thermal pressure relief devices (TPRDs) which release the tank pressure into safety vent lines in the event of a fire, ensuring the tanks do not rupture.
The valve blocks also feature pressure relief devices to vent excess pressure in the event of an overfill – again to the safety vent lines.
They also feature excess flow devices (EFDs). In the event of a catastrophic failure of the high-pressure line from the valve block, the EFD prevents limits the flowrate of hydrogen escaping, minimising the escaped mass before detection.
Hydrogen safety layer two:- sensors and detectors
Hydrogen detectors form the second layer of safety.
Fast response ATEX-rated H2 sensors, along with marine certified smoke/heat detectors and flame IR sensors.
The H2 sensors are used in the engine rooms and the storage areas to detect the slightest leaks and shut the system down before the levels even get near the flammable limit.
Should smoke or flames be detected from other sources, the hydrogen systems are automatically shut down.
Hardwired connections ensure alarms are declared and the H2 system is shutdown safely.
Each cylinder features normally closed valves so shutting the gas off at the source occurs automatically without the need for operator intervention
Hydrogen safety layer three:- leak detection software and control system
Developed from the ground up at CMB Technologies, the H2 control strategy allows for safe and efficient operation of the system.
Years of testing in the automotive sector, teh CMB leak detection and safety strategies provide for static leak detection and dynamic leak detection.
A failure on the static leak detection (checked every power cycle of the engine) will result in the hydrogen system priming then closing the tank solenoids – thereby rendering the H2 system deactivated – until the leak check is passed at the next power cycle. This ensures that small leaks cannot turn into large leaks, the tanks are sealed and the only hydrogen that can escape is the small amount left in the short high-pressure lines and the longer low-pressure lines
During normal operation our dynamic leak detection system continuously compares the measured gas consumption against the usage from the storage cylinders. A discrepancy between those two measurements results in declaring a leak and shutting the H2 system down
The system displays key information in the wheelhouse/control room and allows for operator intervention, such as manual shut down.
Hydrogen safety:- external experts judge the systems
Through hazards identification (HAZID) and hazard and operability (HAZOP) studies, independent experts are called in to agree the safety of vessel operation and refuelling procedures.
Certification is a three to six month process and a mixture of internal and external experts identify potential hazards and threats affecting people, the environment, assets or reputation.
Only when they agree on all aspects of the H2 system operation, and have identified and evaluated problems that may represent risks to personnel or equipment, do they then agree on the mitigations that ensure the vessel is safe to operate.
As part of the certification process, the CMB team completes a Failure Modes Effects Analysis which is also judged in the HAZID and HAZOP process to ensure risks have been assessed and characterised.