Kap 9 Safety

• Evaporated LH2 also heavy at first, but not as heavy as evaporated LNG

• When mixed with air, the cold LH2 gas will eventually become lighter than air —> Can therefore remain at the ground and move horizontally in explosive concentrations

• Evaporated LH2 has much higher reactivity than evaporated LNG at concentrations above 10 %

• boiling point of LH2 is lower than the boiling point and freezing points of N2 and O2 that make up the air. When LH2 is emitted, LH2 will take energy from the air → air will condense or freeze while LH2 will evaporate. With the exception of enclosed spaces, no LH2 puddles are normally formed, but a pile of condensed/frozen air can form.

• can be a challenge especially for enclosed spaces, e.g. so-called Tank Connection Space, TCS —> if large leakage, LH2 that leaks out may remain at the ground along with frozen air, instead of being vented out through a safety mast

• liquid air can become oxygen-rich, and then strong explosions between LH2 and liquid air can occur

• For these reasons, it is very important that large leaks of LH2 must not be able to occur indoors

1) loss of containment

2) flammable mixture with air or oxygen

3) ignition.

These factors need to be avoided

Hydrogen can burn explosively even below 18 % concentration. See below.

0-4 %: cannot ignite

4-8 %: can not burn downwards, only burns upwards. That is, you won't get hit if youstand near a flame. It burns so slowly that you wouldn't normally get pressure build-up.

8-15 %: As you get closer to 15 %, it gradually becomes more and more explosive.The flame can burn both sideways and downwards, and then pressure build-up canoccur.Outdoors you will not get much pressure, indoors it can damage the building. If youstand nearby, you can get burned.

15-60 %: Very powerful pressure can build up  explosions/detonations

60-75 %: same as 8-15 %.

75-100 %: cannot ignite

This creates turbulence, and the explosion accelerates and becomes more violent ifyou have obstacles in an enclosed space

- Inner zone (fatality risk > 10-5/year): This zone should preferably contain the actualfacility, and preferably be fenced.

- Middle zone (fatality risk > 10-6/year): cannot include residential buildings or hotels,only commercial activities, as well as road, quay, railway and recreational areaswhere stays of limited duration are expected

- Outer zone (fatality risk > 10-7/year): housing, smaller shops, etc., may beestablished, but no schools, nursing homes, shopping malls, etc. with largergatherings of the public

The risk of death of a Norwegian 40-year-old is 10-3 per year initially. That is, every 1000 40-year-old will die every year (from illness, accident or other reasons).

If the annual risk of death from accidents at a facility at the border between the middle and outer zone is 10-6 per year, this means that the risk of death for the 40-year-old who lives on the border increases by 10-6. That is, the risk increases from 0.001 to 0.001001 per year, and becomes 0.1 % higher than it was initially

The technology for hydrogen on ships is not well enough developed yet, and we needa larger base of experience to be able to develop safe rules.Prescriptive rules will stop necessary innovation. If there are rules on how to build ahydrogen ship, people will build it like that, without thinking. It kills innovation. Theway it is now, you have to build what you think is a good idea, and be able to showthat it will be safe. You must be innovative and find good solutions, and then seekapproval for your solution. This approval process is called Alternative design process.Moreover, rules will have to be somewhat general, and thus not optimized for allcurrent designs. For hydrogen vessels where safe design can be more challengingthan for diesel vessels, it may be easier to create a safe vessel by function-basedrules than by prescriptive rules.