GRA
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Re: Toyota Mirai Fuel Cell

Mon Jun 17, 2019 5:36 pm

Oils4AsphaultOnly wrote:... prior context trimmed for brevity as acknowledgement of LeftieBiker's point ... I had more to say in my original response, but then felt that the single point was sufficient.

<snip>
explosions and fires are not the same, so stop lumping them together.

Of course they aren't, but rather than minimize the risk I wanted to maximize it. If the number of explosions and fires together is less than the "acceptable" rate just for ICE car fires, then obviously the risk of explosion alone is also less.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

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GRA
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Re: Toyota Mirai Fuel Cell

Mon Jun 17, 2019 5:58 pm

mux wrote:The thing is though, and at the risk of sounding apologetic to CNG or H2, you can design and maintain to reduce those kinds of failures to close to zero. Most CNG tank explosions you're going to see are in very old, badly maintained vehicles. Same should be true for hydrogen at a certain point in the future.

The issue I have with hydrogen in this regard isn't that it is inherently dangerous to have an extremely explosive gas, with on top of that a good 10% of its embodied energy just in gas pressure added to that. It's the fact that you NEED to maintain, inspect and replace these tanks. It is an inherently fragile chain of trust to get to high reliability.

And it gets worse, from an engineering perspective at least. Most tanks are made from carbon fiber reinforced plastics, not metals. CFRP is extremely strong but brittle, meaning any failure will actually be catastrophic.

I note that the Mirai tanks are only certified for 15 years, after which they need to be retired. IDK what if any inspection regime is required, but certainly any such regime needs to be (and eventually will be) designed to ensure adequate safety. As with all other such hazmat, safety rules will be written in blood.

<OT, IIRR Al scuba tanks are also fixed lifetime, unlike steel tanks which can be used as long as they pass the required inspections and tests. While Al scuba tanks are the norm for warm-water recreational diving, I don't use them given the colder, deeper diving I do, which requires both more gas and more insulation, i.e. more weight to compensate for the buoyancy of that insulation. Steel tanks are more negative than Al while also being lighter for the same capacity, so you need to add less lead. In short, there are always design tradeoffs.

As for CFRP, I'd be perfectly happy to use them for scuba even though they're god-awful expensive, owing to their greater capacity (due to being fillable to 4,500-5,500k PSI instead of the 2,400-3,500 for steel tanks, 3,000 for Al). But almost no one outside of the military or other well-funded organizations use them, because aside from being more expensive (and more susceptible to damage from careless handling. They require similar annual visual inspections as with steel tanks), virtually all commercial dive ops have compressors that are incapable of filling them to anywhere near max. pressure, so you'd never get the benefit of the extra capacity. end OT>

mux wrote:There are ways to design much more ductile materials in there to reduce this risk and limit 'wear and tear' failures to (quite fast) leaks instead of explosive decompression. But these tanks would be unreasonably heavy to put in a car (rough rule of thumb: about ~2.5x the weight of CFRP tanks, which already weigh about 100kg for the Nexo and Mirai).

Re weight: Note that a battery pack to provide similar range will weigh 500 kg or more. It's more a space than weight issue; The larger of the two tanks in the Clarity basically eliminates 2/3rds of the trunk's capacity. The Nexo went to three uniformly-sized smaller tanks instead of the Tucson's two differently sized ones, both to make packaging easier and (guessing) probably to benefit from economies of scale.

mux wrote:All of this isn't as much of an indictment of hydrogen as vehicle fuel as Oils4AsphaultOnly implies though. Things can, should and certainly will be engineered to be safe. But clearly, right now, it isn't. Worldwide there are about 100 commercial hydrogen vending stations and about 5000 currently running H2 vehicles. So far we've had 2 stations catastrophically fail. This is an unreasonable failure rate. If this were the aerospace industry, EVERYTHING would be shut down. This is an enormous deal. I think the industry is just 1 Mirai exploding away from basically shutting down.

There are considerably more than 5,000 H2-fueled FCEVs running around worldwide [Edit: Per the IEA report I posted in the H2 and FCEV topic, current world total is 11,200], and the fleet is growing at an increasing pace. China's going big into FCEVs, for commercial vehicles (buses etc.) initially, where BEVs can't meet the operational requirements. BTW, we've only had one station fail; the other explosion was at Air Products H2 production plant in the Bay Area, placed (as it should be) well away from residential areas.
Last edited by GRA on Mon Jun 17, 2019 7:27 pm, edited 1 time in total.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

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GRA
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Re: Toyota Mirai Fuel Cell

Mon Jun 17, 2019 6:22 pm

mux wrote:Really, the big difference between a CNG and H2 tank isn't even the absolute difference in pressure, it's the embodied energy. Natural gas compresses very easily and decompresses fairly benignly because it forms a supercritical fluid at 45 bars, sapping away a decent amount of the compression energy. Upon decompression, consequently, you end up not just with methane in gas form but also a lot of (very cold) liquid at basically atmospheric pressure turning into gas much slower. Effectively, this means that even a 200 bar/3k psi CNG tank will produce a shockwave very similar to an air/nitrogen/h2/whatever tank compressed to about 50 bar.

This doesn't happen to H2. Hydrogen doesn't form anything but a gas down to nearly absolute zero, so ALL of the energy contained in that compression is released upon failure of the tank.

In terms of the energy contained in the shockwave of an explosively decompressing tank, it's not the difference between 200 and 700 bar, it's the difference between 50 and 700. This is why you can walk away basically unscathed from a CNG tank explosion inside your car, but a H2 tank explosion a couple dozen meters away will set off your air bags and cause some considerable personal injury to anyone within a few meters.

Don't forget; there's about 10-15% of the embodied energy of the hydrogen just in compression inside that tank. For a 2.5kg tank (like in the Mirai or Nexo), that's 8kWh or 30MJ of energy that will be distributed over mechanical deformation and a shockwave. This is equivalent to 8kg of TNT detonating in your car.

None of this is to scare anyone per se; any concentrated form of energy will present a risk, but just to put this conversation into context. A H2 tank explosion is not like the CNG tank explosion on video, it's ten times worse.

Uh huh, and that's why all the companies using the tech have designed overpressure systems to prevent such occurrences to the extent possible. Does this mean that tanks will never explode? Of course not, and the number of failures will undoubtedly be greater in countries with lax/corrupt safety regimes.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

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Re: Toyota Mirai Fuel Cell

Mon Jun 17, 2019 6:31 pm

SageBrush wrote:
GRA wrote:The most recent number I saw for the FCEV fleet in California was 6,300. Let's lump both H2 fires and tank ruptures together; if the rate is under 1/1,000, it will be adjudged acceptably safe.

You are making two assumptions that are incorrect:

1. That the ICE fire and high pressure H2 fire have similar characteristics and consequences
2. That the 6,300 FCEV fleet has a year of driving as a denominator.

1. I'm assuming that anyone who is trapped in the car while it burns up will die; anyone who is exposed to a tank explosion may or may not be injured/killed by shrapnel or overpressure. As it is, we have video of fire tests of ICE and H2-fueled cars for comparison, and (at least in the conditions of that test), the H2 is safer, because it vents to air rather than pooling under the car first. Doesn't mean that it will be safer in every situation, but so far, there's no evidence that it's less safe in regular use.

2. As production FCEVs have been on the road in California since 2014, increasing from a few hundreds that year to now over 6,300 with most of them on 3-year leases, we obviously have more than enough data to extrapolate to a yearly rate, especially when the total of such fires to date is ZERO. Per CARB's 2018 annual report, there were 4,411 FCEVs registered in California as of April last year, so there's been a net gain of about 900 [Edit: typo, should be 1,900] since then. Naturally, as the vehicles age, more of them are in the fleet and at least some of them are improperly maintained or repaired we'll start to see some fires and maybe tank explosions, but it hasn't happened yet.
Last edited by GRA on Tue Jun 18, 2019 5:10 pm, edited 1 time in total.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

Oils4AsphaultOnly
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Re: Toyota Mirai Fuel Cell

Mon Jun 17, 2019 7:48 pm

GRA wrote:
Oils4AsphaultOnly wrote:... prior context trimmed for brevity as acknowledgement of LeftieBiker's point ... I had more to say in my original response, but then felt that the single point was sufficient.

<snip>
explosions and fires are not the same, so stop lumping them together.

Of course they aren't, but rather than minimize the risk I wanted to maximize it. If the number of explosions and fires together is less than the "acceptable" rate just for ICE car fires, then obviously the risk of explosion alone is also less.


Worst word salad I've ever seen. Allow me to fill in the blanks to make it obvious how blindly you write.

"Of course fires and explosions are not the same, but rather than minimize the risk of explosion I wanted to maximize the risk of explosion by combining their statistics together."

By combining the risk of fire of cotton with the risk of explosion of a pressure cooker, you don't maximize anything worth discussing. Your statement is so blatantly dumb that I feel I must be dumber to even write this response!
Last edited by Oils4AsphaultOnly on Mon Jun 17, 2019 7:58 pm, edited 1 time in total.
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GRA
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Re: Toyota Mirai Fuel Cell

Mon Jun 17, 2019 7:53 pm

Oils4AsphaultOnly wrote:
GRA wrote:
Oils4AsphaultOnly wrote:... prior context trimmed for brevity as acknowledgement of LeftieBiker's point ... I had more to say in my original response, but then felt that the single point was sufficient.

<snip>
explosions and fires are not the same, so stop lumping them together.

Of course they aren't, but rather than minimize the risk I wanted to maximize it. If the number of explosions and fires together is less than the "acceptable" rate just for ICE car fires, then obviously the risk of explosion alone is also less.


Worst word salad I've ever seen. Allow me to fill in the blanks to make it obvious how blindly you write.

"Of course fires and explosions are not the same, but rather than minimize the risk of explosion I wanted to maximize the risk of explosion by coming their statistics together."

By combining the risk of fire of cotton with the risk of explosion of a pressure cooker, you don't maximize anything worth discussing. Your statement is so blatantly dumb that I feel I must be dumber to even write this response!

Hey, suit yourself and take whatever you want from it. I was trying to over- rather than understate the probability of an accident, so as not to minimize the risk. If you can't understand that, then there's nothing more worth saying. To repeat, so far the # of car explosions and fires of FCEVs and their tanks, at least in California, has been zero. I haven't seen any in other countries either, but won't claim to have the same confidence about those.
Last edited by GRA on Tue Jun 18, 2019 5:11 pm, edited 1 time in total.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

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Re: Toyota Mirai Fuel Cell

Tue Jun 18, 2019 2:06 am

GRA wrote:Uh huh, and that's why all the companies using the tech have designed overpressure systems to prevent such occurrences to the extent possible. Does this mean that tanks will never explode? Of course not, and the number of failures will undoubtedly be greater in countries with lax/corrupt safety regimes.


Of course, this is the essence of my earlier post; *in principle* you can design against anything that goes wrong with anything. That's just engineering. Safety factors all round.

But the point of the post after that is that in order to actually understand the risks, you have to use the right kind of scaling. In Oils4AsphaltOnly's earlier post, there was the implicit assumption that a tank at 700 bar containing H2 is somewhat linearly worse if it fails than a tank at 200 or 300 bar containing CNG. In reality, it's more like a 10X difference, because of the intrinsic properties of the contained fuel. This has large consequences: The type of danger it presents and the degree of safety required.

First off, for weight reasons it is infeasible to construct these tanks out of steel like most high-pressure vessels are. Steel has nice properties, like its toughness (it deforms plastically from yield to failure instead of breaking in a brittle manner) and cheapness. To get a reasonable tank weight, they need to be constructed out of carbon fiber or other fiber reinforced plastic types, which have very high ultimate strength but have brittle failure modes. Aramid is woven in to alleviate this somewhat and get good puncture toughness (hence the nice videos of these tanks getting shot at with high caliber rounds), but this doesn't fundamentally solve the brittle failure mode under pressure. All of this to say: If a tank like this goes, it will go with a bang.

Explosive decompression of most types of pressure vessels is survivable even at point-blank range, maybe with loss of hearing or mechanical damage from shrapnel. But a700 bar H2 tank explosion will not be survivable; the embodied energy simply is too large. Crossing that threshold means that the design of these tanks has to be held to a higher standard. And that's the long explanation of what I meant. In engineering, in order to talk constructively about risks and not just either fearmonger or downplan risks from a feels perspective, you have to understand the risks in all their facets; not just the vague statement 'tanks might explode'.

--------------------

All this being said, it seems like at least the Norway explosion had nothing to do with the pressure vessels and was 'just' a hydrogen explosion. This is a much better outcome than e.g. a pressure vessel failure, because hydrogen leaks can be designed against very easily (just ventilation and roof geometry to prevent build-up of hydrogen gas and the formation of an explosive atmosphere). They dodged a bullet here, unless they find more issues.

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Re: Toyota Mirai Fuel Cell

Tue Jun 18, 2019 3:33 am

mux wrote:All this being said, it seems like at least the Norway explosion had nothing to do with the pressure vessels and was 'just' a hydrogen explosion. This is a much better outcome than e.g. a pressure vessel failure, because hydrogen leaks can be designed against very easily (just ventilation and roof geometry to prevent build-up of hydrogen gas and the formation of an explosive atmosphere). They dodged a bullet here, unless they find more issues.

I understand why a leak might catch fire, but why would it explode ?
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GRA
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Re: Toyota Mirai Fuel Cell

Tue Jun 18, 2019 5:30 pm

mux wrote:<snip detailed reply with which I completely agree>

--------------------

All this being said, it seems like at least the Norway explosion had nothing to do with the pressure vessels and was 'just' a hydrogen explosion. This is a much better outcome than e.g. a pressure vessel failure, because hydrogen leaks can be designed against very easily (just ventilation and roof geometry to prevent build-up of hydrogen gas and the formation of an explosive atmosphere). They dodged a bullet here, unless they find more issues.

For those who missed it, ABG posted an update with more details:
. . . Nel Hydrogen released some preliminary findings as it moves along with its investigation. Fire and explosion safety consultants from Gexcon are working with Nel. It also said the formal investigation "will take time," but there is no hint as to how long it will be.

"Based on what we have seen at the site, we can conclude that neither the electrolyzer nor the dispenser used by customers had anything to do with this incident. We will continue to analyze the other components of the site to further narrow down the source," says Geirmund Vislie, Vice President Consultant of Gexcon AS.

The Kjørbo site also includes a containerized, pressurized alkaline electrolyzer that produces hydrogen in part from solar power. This is delivered by the Nel Hydrogen Electrolyser division.

"We are pleased with the preliminary findings, and our electrolyzer division will now return to business as usual," says Jon André Løkke. . . .
https://www.autoblog.com/2019/06/12/norway-hydrogen-station-explodes-toyota-hyundai-halt-sales/

Anyone seen anything more recent? An arstechnica article dated June 16th included this statement:
The company has not yet been able to rule out whether the stationary low-pressure storage unit, the low-pressure transport unit, the stationary high-pressure storage unit, the various valve panels, or the hydrogen refueling station unit were responsible for the fire.

On its website, Nel said that, "When the root cause is clear, and all the information from the event has been gathered, we will assemble learning points to take forward. These will be shared publicly and specifically within the hydrogen industry at large."
https://arstechnica.com/science/2019/06/after-june-fires-energy-group-says-hydrogen-is-futures-fuel/

I was able to monitor the construction of my local First Element H2 station two ro three years ago, and what I assume was the stationary HP storage unit (a large cylindrical metal tank) was buried in the ground inside a reinforced concrete box with a lid ditto, near the dispenser. Relief valves with the necessary vents were provided. Presumably the box is designed to contain any shrapnel. The low pressure area was behind a solid fence by the time I first looked at the site, so I couldn't see what if any measures were taken there, with pipes connecting the two areas.

The newer, larger capacity First Element fuel stations have gone over to liquid vice gaseous H2 delivery to lower costs, as some of the existing stations were requiring more than one fuel delivery a day to meet demand, and the new stations almost triple total H2 capacity while also adding a second dispenser to increase throughput.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

Oils4AsphaultOnly
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Re: Toyota Mirai Fuel Cell

Tue Jun 18, 2019 6:44 pm

GRA wrote:
mux wrote:<snip detailed reply with which I completely agree>

--------------------

All this being said, it seems like at least the Norway explosion had nothing to do with the pressure vessels and was 'just' a hydrogen explosion. This is a much better outcome than e.g. a pressure vessel failure, because hydrogen leaks can be designed against very easily (just ventilation and roof geometry to prevent build-up of hydrogen gas and the formation of an explosive atmosphere). They dodged a bullet here, unless they find more issues.

For those who missed it, ABG posted an update with more details:
. . . Nel Hydrogen released some preliminary findings as it moves along with its investigation. Fire and explosion safety consultants from Gexcon are working with Nel. It also said the formal investigation "will take time," but there is no hint as to how long it will be.

"Based on what we have seen at the site, we can conclude that neither the electrolyzer nor the dispenser used by customers had anything to do with this incident. We will continue to analyze the other components of the site to further narrow down the source," says Geirmund Vislie, Vice President Consultant of Gexcon AS.

The Kjørbo site also includes a containerized, pressurized alkaline electrolyzer that produces hydrogen in part from solar power. This is delivered by the Nel Hydrogen Electrolyser division.

"We are pleased with the preliminary findings, and our electrolyzer division will now return to business as usual," says Jon André Løkke. . . .
https://www.autoblog.com/2019/06/12/norway-hydrogen-station-explodes-toyota-hyundai-halt-sales/

Anyone seen anything more recent? An arstechnica article dated June 16th included this statement:
The company has not yet been able to rule out whether the stationary low-pressure storage unit, the low-pressure transport unit, the stationary high-pressure storage unit, the various valve panels, or the hydrogen refueling station unit were responsible for the fire.

On its website, Nel said that, "When the root cause is clear, and all the information from the event has been gathered, we will assemble learning points to take forward. These will be shared publicly and specifically within the hydrogen industry at large."
https://arstechnica.com/science/2019/06/after-june-fires-energy-group-says-hydrogen-is-futures-fuel/

I was able to monitor the construction of my local First Element H2 station two ro three years ago, and what I assume was the stationary HP storage unit (a large cylindrical metal tank) was buried in the ground inside a reinforced concrete box with a lid ditto, near the dispenser. Relief valves with the necessary vents were provided. Presumably the box is designed to contain any shrapnel. The low pressure area was behind a solid fence by the time I first looked at the site, so I couldn't see what if any measures were taken there, with pipes connecting the two areas.

The newer, larger capacity First Element fuel stations have gone over to liquid vice gaseous H2 delivery to lower costs, as some of the existing stations were requiring more than one fuel delivery a day to meet demand, and the new stations almost triple total H2 capacity while also adding a second dispenser to increase throughput.


Great, so they've taken significant efforts to protect the fueling stations. That does nothing to help the over 6300 mobile high pressure tanks out in the wild now.
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