Gi-Ho Hwang, head of the Hydrogen System Engineering Team (left) and Myung-Ju Jung, senior engineer from the Fuel Cell System Team (right)
FCEVs is a truly green vehicle which only emits water vapor and even cleans the air as it drives. However, there are concerns about the safety of FCEV. Are FCEVs really as dangerous as some believe? We asked Gi-Ho Hwang, head of the Hydrogen System Engineering Team and Myung-Ju Jung, senior engineer from the Fuel Cell System Team.
Q. Hydrogen energy, is it as dangerous as a hydrogen bomb?
Hydrogen in fuel and Tritium in hydrogen bombs are fundamentally different
Although FCEVs are a promising alternative to conventional gasoline and diesel cars. There is still much skepticism about FCEV’s viability because of safety concerns. There are a significant number of people who think of the hydrogen bomb when FCEVs are mentioned. Is there are justification for this belief? “The word hydrogen is used for both but FCEV and hydrogen bombs are fundamentally different. FCEVs use hydrogen molecules which are stored in a high pressure tank at 700 bar. The hydrogen is depressurized and supplied to the Fuel Cell which is then used to generate electricity. The hydrogen storage tanks were verified thoroughly to ensure safety on a par with conventional cars and CNG vehicles.” Hydrogen bombs require a nuclear bomb to raise the temperature to 100 million ℃ which then triggers nuclear fusion. The Fuel Cell in a FCEV simply creates electricity at a temperature lower than 100℃.
Q. Are hydrogen tanks fire and collision safe?
FCEV fire safety test
There has never been a FCEV accident caused by hydrogen leakage. Hydrogen atoms are 14 times lighter than air so they are dispersed very quickly, which is why hydrogen does not catch fire even if it leaks from a tank. “A hydrogen fire does not happen even if a hydrogen tank catches fire. The hydrogen storage tanks, supply system, and Fuel Cell stack are equipped with a hydrogen leak detection sensor which helps prevents fire. When a hydrogen leak is detected while the FCEV is in operation, the system sends a warning message to the information cluster or automatically shuts off the hydrogen supply to ensure safety.” Hydrogen tanks require ‘High Strength’ to prevent rupture and ‘High Stiffness’ for durability. Strength is defined as the level of resistance to an influence of an external force. Stiffness is the level of resistance maintaining its original shape. The carbon fiber materials used in making hydrogen fuel tanks is as light as a plastic but has six and four times the strength and stiffness of steel, respectively. “When a bullet penetrates a hydrogen tank, it does not explode. Instead, hydrogen leaks out through the bullet hole. In a standard collision test, not even a tiny amount of hydrogen was detected because none had leaked out. Even when NEXO is on fire, a number of safety devices prevent hydrogen from catching fire. Similarly, a hydrogen tank explosion is prevented by quickly releasing hydrogen from the tanks. NEXO was able to receive the EURO NCAP top safety rating because the tests proved its exceptional safety.” According to the Ministry of Land, ？Infrastructure and Transport’s requirements a high pressure tank for automobile application’ has to meet 14 safety requirements including rupture, flame, and bullet penetration. The tanks are also subjected to front and rear collision tests, and extreme temperature (hot and cold) tests. Aiming for the mass production of NEXO, HMG doubled the number of test criteria for a hydrogen tank to ensure compliance with the safety standards of key markets. Approximately 200 different tests were conducted to ensure hydrogen tanks meet the strict safety and durability standards set internally.
Q. What are the durability and safety standards of hydrogen storage tanks?
Hydrogen storage tanks
Hydrogen storage tanks are subject to some of the highest safety requirements and to a thorough certification process. Tanks have to withstand very high pressure, equivalent to being 15km under water and to last for 123 years assuming it is charged once a day. Regulatory requirements for durability over 15 and 20 years is withstanding 4,000 and 5,000 charges in South Korea and EU, respectively. Hydrogen tanks for NEXO were subjected to a wide range of tests including a drop test and extreme temperature tests, whilst charging 45,000 times. Additional tests subjected the tanks to 15,000 more charging to ensure safety and durability beyond the regulatory requirements.
Q. Hydrogen tanks are designed to store hydrogen at extremely high pressures. Does it not pose a safety risk?
Hyundai's hydrogen-fuel-cell-powered Nexo SUV
A Fuel Cell stack requires a minimum pressure and furthermore the pressure for the hydrogen supply needs to increase when higher electricity output is required. It is very difficult to reduce the pressure level down to a desirable level, which is why NEXO’s hydrogen supply system has a two-stage depressurization design. The first stage depressurization unit reduces the pressure from 700 bar to 16 bar. The hydrogen pressure level is further reduced to 1.0 to 1.5 bar right before the hydrogen is supplied into the Fuel Cell stack. Many people have serious concerns about hydrogen fuel tank safety even after they have been made aware of all the evidence of their safety. The safety of FCEVs and hydrogen tanks are excellent as of today. However, Hyundai Motor and Kia Motors are continuing to work on smart hydrogen tanks with realtime status monitoring systems. We are also making R&D efforts to reduce costs and improve storage efficiency, so that FCEVs can be more accessible to customers.
