Both good points. The NHTSA may not know the details of the MS, but they do know how to carry out a safety investigation. Ultimately, their findings will be helpful to Tesla not matter what. IF they find something, they will say how cooperative Tesla was and Tesla will be profusely thankful for the help and make a show of how dedicated they are to safety. Good PR if I ever saw it. If the find nothing wrong, they can still say how cooperative Tesla is, Tesla can make a big deal out of how dedicated they are to safety, and they can dismiss claims of any problem Again, great PR.
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Both good points. The NHTSA may not know the details of the MS, but they do know how to carry out a safety investigation. Ultimately, their findings will be helpful to Tesla not matter what. IF they find something, they will say how cooperative Tesla was and Tesla will be profusely thankful for the help and make a show of how dedicated they are to safety. Good PR if I ever saw it. If the find nothing wrong, they can still say how cooperative Tesla is, Tesla can make a big deal out of how dedicated they are to safety, and they can dismiss claims of any problem Again, great PR.
I will leave it to BillHamp to calculate statistical significance as I honestly couldn't figure out how to calculate it or test for it. However, I'd like to answer a different question.
QUESTION: Based on the given sample size, what is the margin of error?
ANSWER: Let's calculate the margin of error.
Disclaimer: I'm not a statistics guy by any stretch, indeed, needed to google the formula to get the answer.
Source: http://www.dummies.com/how-to/content/how-to-calculate-the-margin-of-error-for-a-sample0.html
Assumptions: For this argument we will assume 3 fires per 19000 Model S. We will assume confidence interval of 95% is desired as per BillHamp's post, and as it seems to be a rather common confidence interval.
Calculations:
Sample Proportion (p) = 3/19000 = 0.000158 = 0.0158%
z* (assuming normal distribution) = 1.96 <---- this number taken from the normal distribution table of z* values
Sample Size (n) = 19000
Margin of Error = z* ( sqrt ( ( p ( 1 - p ) / n )
Margin of Error = 1.96 ( sqrt ( ( 0.000158 ( 1 - 0.000158) / 19000 )
Margin of Error = 1.96 ( sqrt ( 0.000000008309 ) )
Margin of Error = 1.96 ( 0.0000912 )
Margin of Error = 0.000179
Margin of Error = 0.0179%
Therefore, you can conclude with 95% confidence that 0.0158% of Model S cars catch fire, plus or minus 0.0179%
Or, another way of looking at it is you can conclude with 95% confidence that somewhere between -0.0021% and 0.0337% of Model S cars catch fire.
My take: Looks to me that we still have a pretty wide margin of error (so as everyone has been suggesting, we need a larger sample size before we really know what's going on). Based on this calculation, for the next 19000 cars we should expect anywhere between approximately 0 and 6 fires with 95% confidence.
ElectricAvenue
Member
Todd,
I agree the probability of a battery fire will never be zero, and I believe the 3 fires so far are not enough to extrapolate accurately.
Now, I disagree with you saying " The point of mitigation is to reduce the odds to an acceptable level, and Tesla already achieved that" because that is what is under question right now!
And "Likewise, in numerous documented accidents involving the Model S, including some pretty serious head-on crashes, the battery was not involved" what serious head-on crashes? I have only seen 3 or 4 real world head-on crashes which again is not enough to extrapolate but you would like to??
ToddRLockwood
Active Member
By "acceptable level" I meant a level as good as or safer than a gas powered car. Tesla has already built heat & fire mitigation into the battery pack, including individual fusing of every cell, microprocessor management (which will drop cells out of the circuit if it senses trouble), fire-safe compartmentalization (16 sealed battery compartments), and fire retardant expanding foam. In these extremely rare instances where the battery case is compromised, and the internal safety features are disabled, a lithium fire should not be a big surprise. To now make the battery case impenetrable could prove to be too costly relative to the statistical gain. Why don't we put rubber fuel cells inside all gas tanks, and make those gas tanks out of carbon fiber? There is a logical limit to mitigation.
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Here's another data point to consider... How many Tesla Model S have run over objects in the road that damaged the battery case but did not result in a fire?
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roblab
Active Member
Agree with you. I did not dis the government employees. I said they will know next to nothing about the MS. Specifically, I meant the battery, as any of us know next to nothing, also. I said they would have to have Tesla tell them what they were looking at.
I apologize for coming off as being down on this, but the average inspector (with maybe years of experience) will have to be educated. Nothing wrong with that. Hopefully they will see that there is either no problem, or that a problem exists. How one could exist when hundreds of really smart people have worked on it, is beyond me. Just because they are outside the "box" does not make them all of a sudden have greater insight or knowledge. You know that. I can't believe that Tesla engineers are that invested in this brand new technology. They don't even know how long the battery will last. Their boss wants EVERYONE to look at it and find out why it isn't working as planned, even though how it's working is far better than ANY other car in the world. Even "outsiders" are invited to look.
I have worked in a lab for the last 25 years. Inspectors come in and tell me things I already know. They do NOT come in and tell me something I don't know. Nearly always it is about keeping records ("Uh, you don't have any temperature reading on this machine for three days in the last month.") I don't see the value of bringing in NHTSA, no matter how many years' experience they have. They do NOT have experience in safety issues on a Model S battery system. Other than another mouth to say what we pretty much already know, and that mouth belonging to the government so it gets lots of press, it probably won't matter much.
We will wait and see.
jeffhre
Member
"The MS is more prone to fire as a result undercarriage stike than an ICE vehicle. This is what the NHTSA is interested in. This one is harder to assess because we don't know the rate of undercarriage strike and fire in ICE vehicles. That stat may not even exist. However, the NHTSA wants to find out more and so does Tesla."
How do we know the Model S is more prone to fire after strikes in the undercarriage, than ICE vehicles, if as you have stated..."we don't know the rate of undercarriage strike and fire in ICE vehicles," at this point in time?
In fact it would be more accurate to state that we also don't know the rate of undercarriage strike and fires in the Model S, and that may be one of the concerns NHTSA has. Along with a concern with safety of the Model S in accidents now that there are real world examples. And safety with respect to fires, in the event of a Model S accident, and specifically one where the undercarriage is damaged or punctured.
Runarbt
Active Member
Well,
I'd say an ICE car is more vulnerable if you consider the speed a fire developes, and the end result.
One fresh undercarriage ICE fire from Norway, http://translate.google.com/transla...dressa.no/nyheter/trondheim/article784081.ece
I'd prefer Tesla anytime I am to run over road debris, as I'll get a warning that I need to pull over and exit the car.
You dont have to throw yourself out through a burning inferno in a matter of seconds. :-O
This guy ran over something, and noticed flames around the back of his car. Managed to stop, and had to throw himself through flames to get out of the car. Just pure luck he didnt have his kid with him in the back seat, as that could have been fatal
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Hard to get the details on Google Translate, but the general message came through. Yes, the Tesla has some great safety features, the warning to pull over among them. That should be standarda on every car. As to whether this fire (interestingly in Norway) is useful in determining risk of fire in undercarriage strike, it is not.
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Points 1 and 2 are separate hypotheses, that's why they set up the way they are. I'm not saying the MS is more prone, I'm saying that is a hypothesis that would need to be tested and is on of the hypotheses the NHTSA will be testing. You cut off the first part where I made this clear.
dmckinstry
Model X 2019
Hi Rob.
Granted they probably won't find anything that the Tesla engineers don't already know. However, I believe almost anyone doing software development or writing documentation finds debugging their own code or proofreading their own writing as easy as for another party to detect bugs or spot errors. Hopefully a team of engineers would take care of that. However, the added advantage of an outside party just should further convince everyone that Tesla has done everything as well as possible.
Runarbt
Active Member
Well, it does show what the consequences are if an ICE car does catch fire due to debris on the road.
The cars go up in flames, and that very quickly. How often this happens, that is a different thing.
This time the car ran over a loose manhole cover which cracked the fuel tank and generated sparks. http://en.wikipedia.org/wiki/Manhole_cover
We cant say anything useful about determining risk of fire in undercarriage strikes with Tesals either, based on just 3 fires.. ?
Krugerrand
Meow
How interesting and entirely hypocritical and I'm not allowed to say the rest.
An ICE 'running-over-debris-collision-causing-a-vehicle-fire' is not useful in determining risk of fire from an undercarriage strike, YET...it is useful when said incident involves a Model S, such that we have multiple threads with hundreds of posts of *cough* carefully calculated stats and headlines splashed all over the news outlets and Internet stating just how useful that exceedingly flawed data is AND why.
Indeed. I'm kind of surprised we don't have a post yet tallying whether it's more likely that your car will hit a trailer hitch if it's listening to AM vs. FM. (And we all know that the car is immune to collisions if you're listening to Slacker.)
Nothing hypocritical about it. You have presented a single case with no additional support. I only started to suspect Tesla had a design flaw after the third fire. If you want to say that ICE cars can catch fire from underbody damage, then I agree 100%. However, is there a design flaw in this particular make and model ICE that makes it prone to fires? I don't know. One case doesn't mean much. If you can show that this model is higher than average ICE rates, then I'll pat you on the back for a great job with the stats.
You're missing the entire point of my posts. You are trying to use anecdotal evidence rather than statistical evidence. Present the latter, and I'll be happy to listen to what you say. Honestly, I'm tired of explaining it. Respond if you like, but I'm bored with the lack of rigor in the arguments.
You're missing the entire point of my posts. You are trying to use anecdotal evidence rather than statistical evidence. Present the latter, and I'll be happy to listen to what you say. Honestly, I'm tired of explaining it. Respond if you like, but I'm bored with the lack of rigor in the arguments.
Larry
Member
What is the time frame for an NHTSA investigation?
Mods feel free to move if this has been covered elsewhere
Mods feel free to move if this has been covered elsewhere
Krugerrand
Meow
First of all, I haven't presented any 'case' singular or otherwise. That was someone else.
Perhaps the obvious has escaped you? There's only been two fires caused by undercarriage debris hits in the Model S. Second of all, there's only been two fires caused by undercarriage debris hits in the Model S. (The third fire is unrelated) There's been far more than two ICE cars that hit road debris of the same kind (big hunks of metal that caused a lever action and impaling force of such magnitude as to be able to pierce up to 1/4" thickness of aluminum) and started on fire, over the many decades of ICE existence. And yet, it's still a rather rare occurrence because truck bumpers and trailer hitches just don't fall off vehicles in the middle of a highway lane every day of the week, where they are then driven over at high speed. Even with all the trucks and vehicles with trailer hitches driving the many roads of the world, it just doesn't happen very often. Sometimes those bumpers and trailer hitches fall off in the owners' driverways, sometimes on a back road, sometimes they fall off on the highway but bounce to the shoulder of the road, etc... There's a lot of non-middle-of-a-highway-lane places that bumpers and trailer hitches can fall off and land.
If we are to believe as you, that Model S has a design flaw (based clearly on two very rare world experiences) then every single ICE car has that same design flaw - fuel storage on the undercarriage of the vehicle leaving it vulnerable to that big hunk of metal highway debris of truck bumpers and trailer hitches. I suggest we start designing all cars, EVs and ICEs alike, with the fuel storage on the roof of the car, then we need only worry about large metal objects falling from the sky. Oh, and rollovers. And maybe vehicle handling. Hmm...and also fuel storage units coming loose and becoming flying objects. Never mind, bad idea. Let's put the fuel storage in the trunk. Yeah, that'll work!
I'm not missing the point of your posts, I just don't happen to agree with you. That's different. But let me extend my sincerest apologies that I've not been able to make the argument with you rigorous. For some reason I thought we might like to stick to common sense.
In reality I think we should only compare ICE cars that are manufactured by Company whose first letter is 'T' and the first letter of the model is 'M'. That would be comparing apples to apples. We need to throw away all other ICE fires for this discussion, just like throwing away all ICE fires except the ones that happen in collision.
stopcrazypp
Well-Known Member
Does every thread have to turn into something about statistics? I've read lots of those and none of them are conclusive as to whether there's actually an issue (probably because the data is flawed at best and there's still argument over whether 2 or 3 incidents is enough, Poisson distributions and all that). It'll be up to the NHTSA investigation to figure if there's actually a safety issue.
So it is your feeling that there is a flaw. You are entitled to your feelings. To describe it as a flaw and expect others to agree with you means that you must convince the rest of us.
I do not think there is a flaw. Is it possible that the Model S is more susceptible than an ICE vehicle to a fire when the undercarriage is struck? I would agree to that. It's possible.
Your premise:
Damage to battery pack + fire = unsafe/flawed design and Tesla is wrong and needs to correct the flaw
Evidence has shown that:
Damage to battery pack + fire = safe/what Tesla intended to happen in these circumstances
Is there room for improvement? Certainly. Even Tesla and Elon Musk have said that they want the best car out there. Making modifications to the design to make the possibility of an impact causing a fire even less would be a good thing. I, for one opinion, don't see there is a flaw in Tesla's design.
bareyb
Active Member
Not as bored as we are…Every single one of your posts is a negative shot at Tesla. Your purpose here is abundantly clear. Please feel free to leave and never come back.
Please desist from the personal attacks, or your posts will be banished to the Snippiness thread.
Thanks. -mod
Thanks. -mod
