8.1. Is it really safe?
Combustion is not possible in a hydrogen storage that contains only hydrogen. An oxidizer, such us oxygen, with a content of at least 10% oxygen or 41% air is required. Hydrogen can be detected at 25 ppm, and it can only explode above 40000 ppm. Also, a hydrogen fire has significantly less radiant heat than a hydrocarbon fire (e.g. petroleum or natural gas), because hydrogen flames have low radiant heat. This decreases the risk of secondary fires. In addition, every tank deposit or small tank is not a bomb, since lithium-6 (6LiD) is required as fuel to create a hydrogen bomb. Furthermore, hydrogen is 14 times lighter than air and rises at a speed of almost 20 meters per second (six times faster than natural gas). For this reason, with ventilation it can be released and dispersed quickly. That is an important advantage with respect to conventional fuels such us diesel, but also for batteries, because if there is a fire they cannot be released or removed easily.
|Comparison on fuel leak and ignition of hydrogen (left) and gasoline (right). (Michael R Swain. Fuel Leak Simulation)
8.2. Previous accidents: the hindenburg
In 1937, after ten successful trans-Atlantic flights from Germany to the United States, the Hindenburg, a dirigible inflated with hydrogen gas, crashed upon landing in Lakewood, New Jersey. The mystery of the crash was solved in 1997. A study concluded that the explosion was not due to the hydrogen gas, but rather to a weather-related static electric discharge, which ignited the airship’s silver-colored exterior covering.
8.3. Reasons for past accidents
In previous decades, important accidents have occurred involving hydrogen applications. The causes can be categorized into:
- mechanical or material failure
- embrittlement of storage tanks
- boiling liquid expanding vapor explosion
- impact by shock waves and missiles
- human error.
Out of these accident there have been tests developed like the hydraulic crush test and fire tests.
|Wall thickness comparison 350 vs 700 bar cylinders. Matching storage tanks with the operating pressure avoids problems of overpressurization (Powertech)
||Examples of fire and hydraulic crush tests (Powertech)
8.4. Safety considerations onboard Hydroville
- The combustion process of hydrogen is similar to the combustion of diesel. Therefore, the design of the motor only has slight changes, allowing the use of extensive experience on diesel engines.
- The shuttle is a catamaran in which everything is duplicated. Should the hydrogen system fail, the system can be switched over to diesel. Even with only one engine operational, the shuttle can reach 18 knots.
- CMB has explicitly chosen to use the most challenging design: a shuttle with class notation, seaworthy and room for more than 12 people—although this leads to more requirements and regulations that must be fulfilled to guarantee safety.
- Life jackets and rafts are available for 24 people, and the capacity of the vessel is 18 people.
- All radio, navigational and safety equipment is approved for commercial maritime trade (MED – wheel mark).
- An independent classification society (Lloyd’s Register) has reviewed the complete design and investigated the risks. They have investigated the risks (HAZID), and all identified risks are included in the design (HAZOP).
- Components will be maintained to the highest standards and important parts will be replaced at standard time intervals.
- The storage tanks meet the highest standard that is used in the car industry for hydrogen vehicles. Every set is tested for fire resistance, impact and crush resistance and overpressurization.
- All of the current, highest standards for hydrogen cars are being used in the design of the shuttle.
- The tanks can withhold a pressure 1.5 times higher than the maximum we can bunker.
- The 12 tanks increase buoyancy in case of a severe collision.
- The hydrogen storage compartment is closed off from the passengers’ space and is airtight. There are six ventilation shafts foreseen. Therefore, hydrogen cannot accumulate or reach the passengers’ area. The ventilation shafts are located at the highest point of the storage compartment and are spread out over the area.
- In the storage compartment, as well as in the accommodation, hydrogen sensors are installed that will detect any leakage immediately and will shut down all tanks at once.
- There is pressure protection in the pipeline system to ensure that the pressure can never be too high—this system is also active while bunkering.
- Pressure and temperature is constantly monitored in every tank. When the smallest deviation is detected all tanks will be locked.
- In practice, all tanks are closed. Pressure is needed to open the tank valves.
- A series of double-pressure regulators is installed. Should one break down, the next regulator will ensure that pressure stays within the limits.
- Every hydrogen tank is equipped with a fire fuse on both sides. When they reach 120 °C the tanks will discharge the hydrogen safely using the ventilation shafts, causing the hydrogen to self-combust.
- All hydrogen pipes from the storage compartment to the engine are double-walled, so hydrogen from a leak will be contained and discharged safely.
- The engines have been tested extensively over 5 weeks. Every speed and load of the motor has been tested when operating on hydrogen.
- 70 vans are in operation with the same technology, no incident related to the hydrogen-powered engine has been reported so far.
- The hull is built using fire-resistant polyester.
- Smoking is not allowed on board.
- To avoid corrosion, the whole hydrogen system is built using the highest grade stainless steel (316L).
- The hydrogen system will be tested with an inert gas before hydrogen is pumped into the pipelines.
- Only trained and authorized personnel will be allowed to operate the shuttle.
- A GPS tracker with an alarm system is placed on board. In case of fire, breaking off from mooring lines or theft, the competent authorities will be notified.
|previous chapter: hydrogen in shipping
||next chapter: history and future