I sent the Crasche folks an email asking for data documenting the performance of their product. I received the following results as part of a brochure:
LACROSSE CROSS-IMPACT TEST RESULTS (these appear to be stick-to-head):
Sample # Impact Location Cross Velocity (MPH) Severity Index Peak G
Bare Headform Side 38.19 1051 188
Size Small Side 39.94 68 49
Size Large Side 38.64 8 24
LACROSSE BALL IMPACT TEST RESULTS (these appear to be ball-to-head):
Sample # Impact Location Ball Velocity (MPH) Severity Index Peak G
Crosse BXX 1 68.34 278 179
Crosse BXX 2 69.3 208 146
Crosse BXX 3 70.75 294 186
The following sentence was also included in the reply: “Note - these tests are for impact coming onto the head. In a drop test, which simulates a head on collision, a 9 mph event showed an impact reduction of about 25 %.”
For reference, I remember reading somewhere that football helmets tend to increase impact duration from about 3 ms to about 8 ms. Assuming uniform force distribution over the duration of the impact, this amounts to ~60% reduction in peak acceleration (over whatever force domain that acceleration is correct for.) Crasche seems to guard effectively against forces similar to that of a lacrosse stick being swung at the head. Unfortunately, the results of the second test don’t really tell much about the usefulness of the hat, as the Crasche folks seemed to be satisfied with concluding that it’s effective based on seeing a Severity Index (I assume this is based on the head injury criterion?) <300 when taking a lacrosse ball to the head, despite the huge accelerations.
Regarding the drop test − 9 mph gives around 137-82g of acceleration against a hard surface, assuming impact duration of 3-5ms. So we’re looking at 6700-4000N (human head weighs around 5kg). In this domain, we can compare the 25% advertised reduction against the ~60% ballparked estimate for force reduction due to a football helmet.
In summary, the performance appears to be inferior (in terms of pure linear acceleration reduction) to a sports helmet, as one would expect. The hat appears to be more effective against object-to-head impacts (involving smaller forces) relative to impacts that result in the head being brought to a halt from motion (involving larger forces) - perhaps the crushable elements providing the resistance are crushed by the larger forces? My gut says that the performance in a vehicle collision will probably bring the head to a halt against a relatively immobile object, so the hat won’t do much of anything as the crushable bits are crushed too fast to be effective.
Impact duration up to 8ms can’t be important. The brain is sloshing in fluid for this reason. It’s not stopping in anything like 8ms anyway.
I concur with the conclusion that it’s worse than a helmet. Not sure at all why you think it wouldn’t help in an auto collision at all. Less than a football helmet let alone a motorcycle helmet (built for high vs low speed collisions).
My gut says that the performance in a vehicle collision will probably bring the head to a halt against a relatively immobile object, so the hat won’t do much of anything as the crushable bits are crushed too fast to be effective.
I don’t see how the latter clause follows from the former. You said that in the drop test, the impact reduction was roughly 25%. This isn’t huge, but I can’t say it “won’t do much of anything.” Were you thinking of something else to support your claim?
No other source, but keep in mind that helmets are tuned for a certain force level. Too durable and helmet does not reduce peak force as it does not crush. Too weak and it crushes quickly, again with little reduction in peak force. This should just empasize to use the 25% number here though since the forces are more representative.
Redacting “won’t do much of anything” except as implied by 25%, but keep in mind that if peak accelerations are much higher than the given case, the helmet will be less effective due to the above. This may or may not be the case in car crashes depending on speed.
Severity Index (I assume this is based on the head injury criterion?)
Actually, in an email they said the head of NOCSAE did the test, so presumably the NOCSAE Severity Index was used. An NOCSAE article says, “There is no measurable difference in safety of helmets with scores below the 1200 SI threshold.” So in other words, in the test the hats did not protect against any significant damage, because no significant damage was done even without the hat. Despite this, the webpage said said that, “The Crasche hat reduces the severity of blunt force impact by 94%.” I count this deceptive marketing as a strike against the product.
That said, given the low cost of purchasing and wearing the hat, it seems worthwhile for a transhumanist to purchase, simply due the vast gains to be had from a slight reduction in risk of death.
Interesting—thanks for checking this. If the Severity Index is claiming no significant damage below 1200, I think it may be incorrect or may have a different criterion for severe damage. Some helmet standards seem to be fairly insensitive, only accounting for moderate or severe brain injury whereas MTBI can have long lasting effects. Yes, I discount Severity claims as the metric does not appear to give reasonable results. 188g is a crapload of linear acceleration, but metric puts it under threshold...I dont buy it, so am left to judge on peak linear accel instead (shame that rotational accel was not measured...)
My gut says that the performance in a vehicle collision will probably bring the head to a halt...
Presumably, the impact would cause the pedestrian to fly back in roughly the same direction the car was moving during the impact, rather than come to a complete stop. That said, I don’t really know enough about the tests to know if this would make a difference in efficacy. Could you link the exact data you received?
The data is posted above, unlikely to get around to Dropboxing it so I can link (as it was from an email). I agree with you re body movement in a vehicle collision. However, at some point your body would stop. If your head hit something while your body was in motion, thr impacted object would likely have enough strength to bring the head to an abrupt halt. (Contrast with a knife being punched through paper mache—I would expect the force on the lnofe to be much lower than if hitting concrete, as it would go through the paper mache without much velocity change.)
I sent the Crasche folks an email asking for data documenting the performance of their product. I received the following results as part of a brochure:
LACROSSE CROSS-IMPACT TEST RESULTS (these appear to be stick-to-head):
Sample # Impact Location Cross Velocity (MPH) Severity Index Peak G
Bare Headform Side 38.19 1051 188
Size Small Side 39.94 68 49
Size Large Side 38.64 8 24
LACROSSE BALL IMPACT TEST RESULTS (these appear to be ball-to-head):
Sample # Impact Location Ball Velocity (MPH) Severity Index Peak G
Crosse BXX 1 68.34 278 179
Crosse BXX 2 69.3 208 146
Crosse BXX 3 70.75 294 186
The following sentence was also included in the reply: “Note - these tests are for impact coming onto the head. In a drop test, which simulates a head on collision, a 9 mph event showed an impact reduction of about 25 %.”
For reference, I remember reading somewhere that football helmets tend to increase impact duration from about 3 ms to about 8 ms. Assuming uniform force distribution over the duration of the impact, this amounts to ~60% reduction in peak acceleration (over whatever force domain that acceleration is correct for.) Crasche seems to guard effectively against forces similar to that of a lacrosse stick being swung at the head. Unfortunately, the results of the second test don’t really tell much about the usefulness of the hat, as the Crasche folks seemed to be satisfied with concluding that it’s effective based on seeing a Severity Index (I assume this is based on the head injury criterion?) <300 when taking a lacrosse ball to the head, despite the huge accelerations.
Regarding the drop test − 9 mph gives around 137-82g of acceleration against a hard surface, assuming impact duration of 3-5ms. So we’re looking at 6700-4000N (human head weighs around 5kg). In this domain, we can compare the 25% advertised reduction against the ~60% ballparked estimate for force reduction due to a football helmet.
In summary, the performance appears to be inferior (in terms of pure linear acceleration reduction) to a sports helmet, as one would expect. The hat appears to be more effective against object-to-head impacts (involving smaller forces) relative to impacts that result in the head being brought to a halt from motion (involving larger forces) - perhaps the crushable elements providing the resistance are crushed by the larger forces? My gut says that the performance in a vehicle collision will probably bring the head to a halt against a relatively immobile object, so the hat won’t do much of anything as the crushable bits are crushed too fast to be effective.
Impact duration up to 8ms can’t be important. The brain is sloshing in fluid for this reason. It’s not stopping in anything like 8ms anyway.
I concur with the conclusion that it’s worse than a helmet. Not sure at all why you think it wouldn’t help in an auto collision at all. Less than a football helmet let alone a motorcycle helmet (built for high vs low speed collisions).
The subarachnoid space, where cerebrospinal fluid sloshes, is 3-6mm in adults. Along with dura, that gives ~1cm.
9mph
What about the rest of the brain deformation?
The brain deforming is basically the problem, but it does deform and that is going to change how it is affected by impact.
But you’re right that 8ms is a relevant impact reduction.
Thanks for researching this.
I don’t see how the latter clause follows from the former. You said that in the drop test, the impact reduction was roughly 25%. This isn’t huge, but I can’t say it “won’t do much of anything.” Were you thinking of something else to support your claim?
No other source, but keep in mind that helmets are tuned for a certain force level. Too durable and helmet does not reduce peak force as it does not crush. Too weak and it crushes quickly, again with little reduction in peak force. This should just empasize to use the 25% number here though since the forces are more representative.
Redacting “won’t do much of anything” except as implied by 25%, but keep in mind that if peak accelerations are much higher than the given case, the helmet will be less effective due to the above. This may or may not be the case in car crashes depending on speed.
Actually, in an email they said the head of NOCSAE did the test, so presumably the NOCSAE Severity Index was used. An NOCSAE article says, “There is no measurable difference in safety of helmets with scores below the 1200 SI threshold.” So in other words, in the test the hats did not protect against any significant damage, because no significant damage was done even without the hat. Despite this, the webpage said said that, “The Crasche hat reduces the severity of blunt force impact by 94%.” I count this deceptive marketing as a strike against the product.
That said, given the low cost of purchasing and wearing the hat, it seems worthwhile for a transhumanist to purchase, simply due the vast gains to be had from a slight reduction in risk of death.
Interesting—thanks for checking this. If the Severity Index is claiming no significant damage below 1200, I think it may be incorrect or may have a different criterion for severe damage. Some helmet standards seem to be fairly insensitive, only accounting for moderate or severe brain injury whereas MTBI can have long lasting effects. Yes, I discount Severity claims as the metric does not appear to give reasonable results. 188g is a crapload of linear acceleration, but metric puts it under threshold...I dont buy it, so am left to judge on peak linear accel instead (shame that rotational accel was not measured...)
Presumably, the impact would cause the pedestrian to fly back in roughly the same direction the car was moving during the impact, rather than come to a complete stop. That said, I don’t really know enough about the tests to know if this would make a difference in efficacy. Could you link the exact data you received?
The data is posted above, unlikely to get around to Dropboxing it so I can link (as it was from an email). I agree with you re body movement in a vehicle collision. However, at some point your body would stop. If your head hit something while your body was in motion, thr impacted object would likely have enough strength to bring the head to an abrupt halt. (Contrast with a knife being punched through paper mache—I would expect the force on the lnofe to be much lower than if hitting concrete, as it would go through the paper mache without much velocity change.)