Hydrogen vs. Battery

[CalDreamin]

From the article linked: "The total mass of the hydrogen was estimated at 10 to 20 kg hydrogen."

That means somewhere between 1/6 and 2/3 of the hydrogen actually burned in the explosion.

Right, in this particular incident, some of the leaked hydrogen was not involved in the explosive blast. It might have escaped to the atmosphere without igniting. Or it might have burned without being part of the explosive blast.

And not all of the hydrogen in the system escaped. To get 3.5-7 kg of hydrogen into the air, it has to come out of the tank, which will drop the pressure significantly. There is definitely a danger of a large explosion, if the tank is full and ruptures, but I think the frequency of dangerous fires and explosions may be less than with gas.

I agree that the probability of FCV H2 explosions will likely be lower than gasoline fires in an ICE car, assuming the FCVs are well engineered. The point I'm making is that the potential severity of a H2 explosion from a FCV or a H2 fueling station can be far worse than any fire involving a gasoline ICE car.

The reason is that gas pools, evaporates, and burns. The range of fuel/air mixtures that burns for gas is smaller, but because it can pool and continually evaporate under normal conditions, it can have a fume cloud in a burnable state for quite some time, and once it gets started it burns hot for quite some time.

Right, burning for quite some time instead of having much of it burn in a fraction of a second in a supersonic detonation shock wave is the difference between a liquid fuel fire and a flammable gas explosion. Which one would be worse to live across the street from?

Gasoline is very dangerous, and a well engineered tank and safety system for a FCV may well be less risky than having gasoline everywhere in relatively unprotected tanks. In a typical car accident with a hydrogen tank, it is less likely that the tank will fail at all, and if it does, it will probably be a small enough leak or a safety valve that releases hydrogen slowly enough that ignition won't be catestrophic.

The PRD (Pressure Relief Device = safety valve) in a FCV exists only to relieve in specific external fire impingement scenarios. The PRD plug has to melt at high temperature for it to activate. Judging from the Honda CNG explosion caused by an external fire, these types of PRDs apparently don't protect against all fire impingement scenarios. That doesn't surprise me because there can be variations in the intensity of impinging flames, and the orientation of the flames relative to the PRD location on the tank.

The H2 FCV PRD does not protect against other overpressure scenarios because it's not a general-purpose relief device. If the FCV H2 tank or its associated valves, fittings, or piping is catastrophically ruptured by the impact forces of a collision (or from vibration fatigue, or from brittle fracture, or...) then the PRD does nothing at all to help.

A slow leak from a 10,000 psig H2 tank has to be an extremely small breach. There was an incident many years ago that I was involved with, where H2 in a 2000 psig vessel leaked from what a witness later told me was "a hole the size of a period on a page." This ==> . This leak led to an emergency evacuation of all personnel within a large radius. We can manage these risks with all the safety monitoring, systems, inspections, and procedures in remote industrial settings. Joe Sixpack's FCV car won't have the benefit of all that.

It's certainly possible for a H2 tank in a FCV to slowly leak out its contents with no fire at the leak location. In that case, hopefully the FCV was stored outdoors. Because if it's stored in a garage, the H2 can pool along the ceiling until it finds an ignition source, and it doesn't take much energy to ignite H2-air mixtures. An ordinary light bulb or ceiling fan can trigger ignition.

 

[adiggs]

...
I agree that the probability of FCV H2 explosions will likely be lower than gasoline fires in an ICE car, assuming the FCVs are well engineered. The point I'm making is that the potential severity of a H2 explosion from a FCV or a H2 fueling station can be far worse than any fire involving a gasoline ICE car.

.

From the detailed accident description linked above, I found this telling quote:
"7.0 IGNITION
Hydrogen-air clouds are known to ignite quite easily due to the low ignition energy. This is confirmed by Ordin[7] who has reviewed NASA's experience with accidental release of hydrogen. He found that 64 out of 83 releases ignited."

That doesn't mean that we would see the same behavior with FCV accidental releases of hydrogen, nor does it mean that we won't see an even higher %. The only conclusion I draw from the statement is that simply dismissing ignition of hydrogen in an accidental release is unwarranted.


The rest of the article is also an interesting read. There were some unreal forces at work in that building (explosion strong enough to literally raise the roof, about 1.5 meters, and enough to shear off a rather large pipe; among other effects).

I'm not normally one to get involved in NIMBY, but I'll be attending public meetings around where I live and work if it looks like compressed hydrogen is coming to my neighborhood. I wonder if we'll see businesses adopt a stance that the consequences of a tank rupture are potentially so high, that FCV's are treated like dangerous weapons, and not permitted on company grounds. Being unable to use an FCV to get to work would certainly put a damper on their adoption.

 

[JRP3]

Most Tesla drivers I know aren't like this at all.

You mean they don't like to hear factual evidence from knowledgeable sources?

 

[djp]

This risk assessment put the number of hydrogen explosions at 2,461 per year (in Germany alone) if all cars switched to FCV. Of these, five per year are considered severe, causing destruction of the car or lethal injuries.

http://vgr.ing.unipi.it/ichs/images/stories/papers/199.pdf

Taking into account the population of the cars in circulation and the possible increase of hydrogen-driven vehicles among the whole population, the frequency of severe accidents represents a non-negligible risk for a person. For example, in Germany there are about 45 million passenger cars in circulation, the risk of hydrogen explosion of the car (EXP3) with lethal casualties would represent (in the worst scenario) five events every year.

 

[miimura]

This risk assessment put the number of hydrogen explosions at 2,461 per year (in Germany alone) if all cars switched to FCV. Of these, five per year are considered severe, causing destruction of the car or lethal injuries.

Taking into account the population of the cars in circulation and the possible increase of hydrogen-driven vehicles among the whole population, the frequency of severe accidents represents a non-negligible risk for a person. For example, in Germany there are about 45 million passenger cars in circulation, the risk of hydrogen explosion of the car (EXP3) with lethal casualties would represent (in the worst scenario) five events every year.

http://vgr.ing.unipi.it/ichs/images/stories/papers/199.pdf

What is the existing number for lethal incidents involving gasoline or diesel vehicle fires per year in Germany? The relative figure of increase or decrease is probably more important than the absolute number.

 

[Aury]

You mean they don't like to hear factual evidence from knowledgeable sources?

With all due respect JRP, do you want me to treat you like an adult or a child. If you want me to respect you, then use proper arguments. Caldreamin used an ammonia plant explosion from 1985 as an argument for the safety of hydrogen cars, it's fear mongering and I won't participate in that.

There have been hundreds of accidents in airplanes with lithium battery cargo, some fatal. A lithium battery brought down a 747 UPS aircraft, the FAA has banned the use of large lithium cargo in civilian aircraft.

You don't see people use that as an argument against EV cars, because they're not directly related. So why can't you be a little more objective.

 

[Doug_G]

With all due respect JRP, do you want me to treat you like an adult or a child. If you want me to respect you, then use proper arguments. Caldreamin used an ammonia plant explosion from 1985 as an argument for the safety of hydrogen cars, it's fear mongering and I won't participate in that.

With all due respect, the incident is relevant because of the similar amount of hydrogen and pressurization. If somehow a hydrogen tank somehow erupted in a residential garage the destruction would be similarly catastrophic.

There have been hundreds of accidents in airplanes with lithium battery cargo, some fatal. A lithium battery brought down a 747 UPS aircraft, the FAA has banned the use of large lithium cargo in civilian aircraft.

Are you kidding? You dismiss the plant explosion as irrelevant then jump to aviation? Commercial aircraft are very well built but inherently fragile. It takes very little to cause an aircraft incident to turn fatal. People have died due to a faulty toilet pump motor. Even the smallest explosion could cause decompression, with the potential additional damage caused to aircraft electrical and hydraulic control lines, etc.

You don't see people use that as an argument against EV cars, because they're not directly related. So why can't you be a little more objective.

I think the arguments presented here have been quite objective. Please look in the mirror.

 

[ElSupreme]

Caldreamin used an ammonia plant explosion from 1985 as an argument for the safety of hydrogen cars, it's fear mongering and I won't participate in that.

But it is relevant. Compressed gas at 10,000 psi can be very dangerous if the pressure vessel ruptures. Hydrogen is very explosive in many air mixtures. It also has very low energy requirements for it to ignite. These don't change when you are talking about a car, or a industrial facility.

In fact a stationary industrial facility is a SAFER place. You don't have to worry about vibration, collisions, extreme temperatures.

Your mention of Li-Ion fires on airplanes IS an example of Li-Ions not being safe! They grounded all the 787s after the fire and had a fix for the failure. There have been 3 Tesla battery fires. They aren't 100% safe. But they only burn, and have relatively low energy output for a vehicle.

Hydrogen, and gasoline also have these probelms but the energy storage is so much greater, and can be released (in the case of hydrogen) so much faster. That makes these failures so much more dangerous. It is an issue.


Personally I don't like driving around with a propane tank in my car. I wouldn't ever consider driving with a 10,000 psi Hydrogen tank. If you have a wreck, and the tank ruptures you are going to have a major explosion (just gas expansion) then fireball and subsequent explosion when the hydrogen ignites.

 

[richkae]

This risk assessment put the number of hydrogen explosions at 2,461 per year (in Germany alone) if all cars switched to FCV. Of these, five per year are considered severe, causing destruction of the car or lethal injuries.

http://vgr.ing.unipi.it/ichs/images/stories/papers/199.pdf

There is more detail that is very relevant.
They model 5 different possible hydrogen explosion events ( beyond fires ), with decreasing likelihood. It is the events EXP3-EXP5 that they expect only 5 per year of.
EXP1 likely to kill or injure the people in car.
EXP2 likely to kill or injure people within 10m
EXP3 likely to kill or injure people within some unspecified range between 10m and 80m
EXP4 likely to kill or injure those within 80m
EXP5 likely to kill or injure those within 100m

That is a lot different than a gasoline fire.

 

[Yggdrasill]

With all due respect JRP, do you want me to treat you like an adult or a child. If you want me to respect you, then use proper arguments. Caldreamin used an ammonia plant explosion from 1985 as an argument for the safety of hydrogen cars, it's fear mongering and I won't participate in that.

There have been hundreds of accidents in airplanes with lithium battery cargo, some fatal. A lithium battery brought down a 747 UPS aircraft, the FAA has banned the use of large lithium cargo in civilian aircraft.

You don't see people use that as an argument against EV cars, because they're not directly related. So why can't you be a little more objective.

Showing the effects of roughly the same amount of hydrogen as you would find in a hydrogen fuel cell vehicle exploding is equivalent to showing roughly the same amount of li-ion batteries as you would find in an EV burning. That's not what you did. Instead you showed the effects of a fire on a plane, coincidentally started by li-ion batteries burning.

There's a vast difference between fear mongering and looking at the worst-case effects of a FCV hydrogen explosion. Explosions *will* happen. You seem unable to accept that.

 

[Aury]

I think the arguments presented here have been quite objective. Please look in the mirror.

No they haven't, I have gotten 2 extremely disrespectful messages in my inbox, telling me to keep my mouth shut. My guess is this is why I have that red rating under my name.

They know who they are and I don't need to name names, people haven't been objective. I won't participate in the thread anymore, people are fear mongering and like I said before, I refuse to participate in that, it's childish and it's unproductive.

 

[Doug_G]

You just fear-mongered about lithium batteries yourself, implying that risks in aviation and automobiles are similar. They are orders of magnitude different. An incident that could lead to the destruction of an airplane would simply cause an automobile to pull over to the side of the road.

You have a red bar because more than one moderator gave you negative rep. They included a message explaining why and who they were (as is our policy).

You seem to be the least objective person here. You have completely ignored factual evidence provided by others, or dismissed it as irrelevant when it was anything but.

I'd like nothing better than for hydrogen to be successful; unfortunately there are simply too many large barriers to its adoption. Any one of these barriers is a show-stopper. If there was only one such barrier then I would have hope that it could be overcome. However there are simply too many problems, as have been outlined at length in this thread.

 

[djp]

What is the existing number for lethal incidents involving gasoline or diesel vehicle fires per year in Germany? The relative figure of increase or decrease is probably more important than the absolute number.

The paper doesn't do a direct comparison, so it's tough to line up their classification scale with other studies. In general, the numbers seem to be in line with the intuitive reasoning on this form - the frequency of incidents would be lower than gasoline but risk of catastrophic events higher.

I'm surprised that most tests of hydrogen tanks consider a rifle bullet impact, but not a "pole vault" impact similar to the Model S road debris strikes. A pole vault would impale the hydrogen tank with the full force of the car's mass, causing a lot more damage than the mass of a bullet.

 

[CalDreamin]

This risk assessment put the number of hydrogen explosions at 2,461 per year (in Germany alone) if all cars switched to FCV. Of these, five per year are considered severe, causing destruction of the car or lethal injuries.

http://vgr.ing.unipi.it/ichs/images/stories/papers/199.pdf

Good find. In my business, we also use a similar methodology for risk assessments.

A word of caution. Risk assessments for relatively rare, high consequence events are not accurate to 4 significant figures. Not even close. We have dusted off previous risk assessments (completely different risks, not H2 FCV), updated the probabilities and consequences, and found the overall risk score to increase by an order of magnitude.

If one also considers failure modes not previously accounted for in an overall risk assessment, the risk score might increase yet again, sometimes by another 1-2 orders of magnitude. Space shuttle SRB safety during subfreezing launches comes to mind, as a familiar example.

Risk assessments are useful tools. But for rare, high consequence events they might be at best order of magnitude accurate, particularly for systems and events where one doesn't have a lot of historical data.

Sometimes, the (perceived) magnitude of a rare but notorious event has more impact on public perception and policy than more common place, more damaging on a cumulative basis, but less terrifying events. One Chernobyl event can be perceived as worse than the millions of people killed by coal smoke.

 

[miimura]

I think explosion risk by tank rupture is being overblown here. A far more likely occurrence is a relatively slow leak. The problem with a slow leak is that Hydrogen rises. My garage has a 18 foot ceiling and my tankless gas water heater and has furnace are within 4 feet of that ceiling. There is no escape for that gas because the garage is completely finished with drywall and painted. Obviously the garage door has lots of air leaks but there is more than 9 feet of air space above that. I know gas gets trapped up there because my furnace had a slow leak at the flex line connection a few months after installation. Since nat-gas rises and has a strong smell, I was able to smell it and call the utility and they found the leak for me. I would be very wary of parking a H2 fueled vehicle in my garage given the circumstances.

 

[NickInLab]

With all due respect JRP, do you want me to treat you like an adult or a child. If you want me to respect you, then use proper arguments. Caldreamin used an ammonia plant explosion from 1985 as an argument for the safety of hydrogen cars, it's fear mongering and I won't participate in that.

Aury, I really think you don't fully appreciate the safety hazards associated with high pressure gases in general and hydrogen in particular.

First of all, when compressed gas containers fail, they usually fail catastrophically. Failure of a cylinder of even an inert gas (say, any noble gas like Argon or Krypton) will appear to the lay bystander as an explosion. That is, even if the gas does not combust, the rate of volume expansion will be so high that witnesses will characterize it as an explosion. It's not like a balloon popping, and it's definitely not something you want to be near. Failure of a compressed gas cylinder near the outlet can easily send the valve assembly through several *feet* of concrete. I repeat: this is a hazard even for inert gases.

Second, as others have already pointed out, hydrogen solvation in metals has negative effects on their material properties. This is just an empirically observed fact. Related to this, people (including ones on this forum) are very casually mentioning pressures like 10k psi for hydrogen storage in FCVs. That's an very high pressure. Compressed gas for lab use usually comes in rented cylinders at only up to about 6k psi. When the cylinders are empty, they go back to the gas supplier, where they are periodically inspected and refilled. Are hydrogen cylinders in cars (which are storing gas at above-normal pressures) going to be periodically removed and inspected? That sounds expensive, so there will be a big incentive to cheat the inspection.

Finally, if you want to get an estimate for the the failure rate of FCV hydrogen containers, look at the SCUBA industry as a best case scenario. Filling a gas cylinder causes strain in the metal (eventually leading to metal fatigue--that's why DOT requires inspections), and that's about the only use I know of where the cylinders will be refilled as often as those in an FCV. SCUBA tanks also have the advantage (compared to FCVs) of only being used with mixtures of oxygen and nitrogen, and at lower pressures.

So, to review, without saying *anything* at all about the combustability of hydrogen, you're talking about storing a gas which causes progressive damage to its container. Which is being stored at pressures above those usually used in industry. Which is being strained much more often than normal. Which is (probably) being inspected less frequently than normal. And you think this is a *good* thing? Compare this to BEVs: We know what happens in a really bad collision (not much, just some f*reworks).

This isn't fear mongering. This is solid science and engineering (and statistics). Fortunately there's a simple way to solve all these problems: Bond the hydrogen to some carbon. It's called "natural gas," and it's been used to power vehicles for a long time now. The energy density is higher (so you don't need such high pressures to get decent range), and the hydrogen is trapped in a molecule (so it can't dissolve into the metal container). It's less explosive and has a higher activation energy for combustion. And, since the only commercially-viable source of hydrogen is natural gas, you're saving energy, to boot.

There's a saying in engineering "Faster, Better, Cheaper: Pick two." Compared to hydrogen, compressed natural gas is like getting all three.

 

[JRP3]

And at that point the more efficient use of NG for transportation is in a combined cycle generating plant charging EV's. That way you also avoid carrying around a pressurized tank of NG, not to mention the potential for leaks when fueling, which was a common problem with a number of CNG vehicles.

 

[jerry33]

The biggest safety issue I see here is around maintenance and inspection. High pressure cylinders require periodic inspection, sure, during the warranty period on a FCV this is likely to happen, but imagine the 20 year old FCV that some teenager bought used and is planning to drive in to the ground... If his gasoline tank rusts out and fails it's a minor environmental issue, if his H2 tank fails... well he could take quite a few innocent people with him.

Agreed. The reason we don't use steam cars and tractors is that unless maintenance is perfect they have a tendency to rupture violently. The big difference between steam and hydrogen is that steam doesn't support combustion. I really, really don't want to have a 10,000 psig tank in the car next to me on the freeway.

 

[Reykjavik]

Right, in this particular incident, some of the leaked hydrogen was not involved in the explosive blast. It might have escaped to the atmosphere without igniting. Or it might have burned without being part of the explosive blast.


I agree that the probability of FCV H2 explosions will likely be lower than gasoline fires in an ICE car, assuming the FCVs are well engineered. The point I'm making is that the potential severity of a H2 explosion from a FCV or a H2 fueling station can be far worse than any fire involving a gasoline ICE car.


Right, burning for quite some time instead of having much of it burn in a fraction of a second in a supersonic detonation shock wave is the difference between a liquid fuel fire and a flammable gas explosion. Which one would be worse to live across the street from?

The fact that not all the hydrogen burned in the explosion is very important, you can't compare an accident where 10kg exploded to an accident where only 10kg is in the system to begin with. If only half the fuel burns in the average explosion, then we only have to worry about half of the fuel in the tank.

We also have to decide between a lower probability higher impact event and a higher probability lower impact event, and what the exact probabilities and impacts are is important. I'd rather have a 1/100,000 chance of 3 people dying than a 1/10,000 chance of 1 person dying. Sure you can go with a minimax strategy, but it won't get you the best expected outcome.

We have three technologies, we have gas which we know is very dangerous, but we've gotten used to it, we have hydrogen, which we know is dangerous but we aren't sure quite how risky it is, and we have battery electric, which we know is pretty damn safe. The clear choice is to go with batteries. But one of the things we need to do is shake people out of their complacency, and asserting that hydrogen is more dangerous than gasoline without supporting it with evidence is not helpful in that regard. Hydrogen may ultimately be more dangerous, but I haven't seen enough evidence to support that hypothesis.

 

[Yggdrasill]

The fact that not all the hydrogen burned in the explosion is very important, you can't compare an accident where 10kg exploded to an accident where only 10kg is in the system to begin with. If only half the fuel burns in the average explosion, then we only have to worry about half of the fuel in the tank.

How much of the hydrogen will explode is impossible to say. It will be somewhere between 0 and 100%, and that's all that's certain. A quick release of the entire content of the hydrogen tank will probably be closer to 100%. In such an event you will have jets of hydrogen shooting out of the tank, rapidly mixing the hydrogen with air. Most/all of the hydrogen can end up in an explosive mixture with air, due to the wide envelope of the explosive mix. (And the rest of the hydrogen will merely be flammable.) In a slow leak, most of the hydrogen will most likely rise high into the air before it has a chance to burn or explode.

Also, in the future there may be more hydrogen in vehicles. An SUV might need 15-25 kg to have a good enough range while towing. A semi might need 100-200 kg. And what about situations like multi-car pileups? You could have multiple vehicles leaking hydrogen at the same time.

We also have to decide between a lower probability higher impact event and a higher probability lower impact event, and what the exact probabilities and impacts are is important. I'd rather have a 1/100,000 chance of 3 people dying than a 1/10,000 chance of 1 person dying. Sure you can go with a minimax strategy, but it won't get you the best expected outcome.

Lower probability, higher impact events aren't ideal. Consider airline transportation - it's one of the safest things people do, yet airline accidents are quite feared. This fear manifests in very expensive safety protocols and some people won't set foot on an airplane. Even if the number of deaths is lower, the impact to society can be higher.

We have three technologies, we have gas which we know is very dangerous, but we've gotten used to it, we have hydrogen, which we know is dangerous but we aren't sure quite how risky it is, and we have battery electric, which we know is pretty damn safe. The clear choice is to go with batteries. But one of the things we need to do is shake people out of their complacency, and asserting that hydrogen is more dangerous than gasoline without supporting it with evidence is not helpful in that regard. Hydrogen may ultimately be more dangerous, but I haven't seen enough evidence to support that hypothesis.

I don't believe anyone has said that the vehicle fires/explosions would be more dangerous than gasoline, although that is a real possibility. When it comes to fueling stations, they will almost certainly be waay more dangerous. The worst that happens to a gas station is that the pumps catch on fire and burn intensely. People have died in such fires, but it's a rare occurence. All the gasoline is usually stored in underground tanks, where there isn't much oxygen, and you need to actively pump the gasoline out of the tanks to fuel the fire. Once the pumps stop the fire starts to die down.

Imagine however if a large-ish hydrogen fueling station with 2000 kg of stored hydrogen catches on fire, or is hit by a semi at 60 mph, or something along these lines. (2000 kg would be enough to fuel ~400 vehicles, maybe less than 100 if a significant number are semis.) A common occurence will be for the actual pumps to get damaged in collisions, but it's pretty certain that there will be an automatic stop-valve for such occasions. (Even so, stop valves can malfunction, so it's nowhere near as safe as gasoline.) Hydrogen tanks usually aren't underground, so they are much more suceptable to mechanical and fire damage. And you just need localized damage for there to be a leak, resulting in a fire, which could compromise the tanks and cause an explosion. Imagine if a nutjob goes postal, pulls out a 44. Magnum and starts shooting at the storage tanks.

2000 kg of hydrogen can level *a city block*. All you need is 2-3 things to go wrong for the hydrogen to go off.