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Old 04-19-2018, 12:10 PM   #1
JazzJedi
 
Join Date: Dec 2014
Default Blunt Trauma

I've been playtesting a hack I made to simulate blunt trauma and thought I would share. For years, I used T-bone's Edge Protection rule, but I found this unsatisfactory for ballistic armor with trauma plates and other rigid armor especially with high DR ultratech armors, such as TL 10 Combat Hardsuit (DR 75) which would convert to DR 60 EP 25. This means that there is no blunt trauma from the first 60 points of damage, which doesn't seem realistic to me.

So I came up with a new way of simulating blunt trauma that uses a similar system to the RAW but modifies the amount of damage it takes to get 1 point of injury from blunt trauma. It has the complication of adding a Blunt Trauma (BT) rating to body armor. This handily eliminates the need for the distinction between flexible and rigid armor, which makes sense. Most "rigid" armors are flexible and dent and deform quite a bit when struck. They don't spring back to their original shape, but they still convey blunt trauma through them, before they are penetrated.

For every full ​multiple of an armor's BT you take of crushing, cutting, impaling, or piercing damage you suffer 1 HP of injury due to blunt trauma.

BT eliminates the need for the distinction between flexible and rigid armor, as these exist on a spectrum anyway. Most flexible armors have a BT equal to 1/6 to 1/4 of its DR, or 1/2 to 1/3 for most rigid armors. The minimum BT is 1, which means that the armor offers no protection from crushing damage and converts the other forms of damage into crushing. This is appropriate for light mail and thin cloth armor.

I based the BT ratings partly off the NIJ standard, where the deformation a projectile creates upon impact cannot exceed 44mm (1.73 in.). A penetration of 44mm is known to cause broken ribs and internal bleeding and possible death, this must be close to a major wound, which is 5-6 points of damage for an average person with 10 HP. So a BT equal to 1/5 DR means that if an attack does damage equal to the armor's DR, the target will take 5 points of blunt trauma. I know that armor can deform considerably more than this before being penetrated, but the math is not linear anyway, and this is just a rough approximation for playability.

You could even split the BT rating to cover different damage types.

Some Examples:
TL2 Light Mail is DR 6, BT 1
TL4 Medium Plate is DR 12, BT 4
TL8 Assault Vest is DR 15, BT 3
Trauma Plates add +25 DR (semi-ablative), +5 BT (1/5 of DR)
TL10 Combat Hardsuit: DR 75, BT 15

I put up more examples on my webpage, but this idea has not been fully fleshed out or extensively playtested. Any feedback would be welcome.
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Old 04-19-2018, 12:50 PM   #2
Tomsdad
 
Join Date: Jan 2010
Location: Brighton
Default Re: Blunt Trauma

Quote:
Originally Posted by JazzJedi View Post
I've been playtesting a hack I made to simulate blunt trauma and thought I would share. For years, I used T-bone's Edge Protection rule, but I found this unsatisfactory for ballistic armor with trauma plates and other rigid armor especially with high DR ultratech armors, such as TL 10 Combat Hardsuit (DR 75) which would convert to DR 60 EP 25. This means that there is no blunt trauma from the first 60 points of damage, which doesn't seem realistic to me.

So I came up with a new way of simulating blunt trauma that uses a similar system to the RAW but modifies the amount of damage it takes to get 1 point of injury from blunt trauma. It has the complication of adding a Blunt Trauma (BT) rating to body armor. This handily eliminates the need for the distinction between flexible and rigid armor, which makes sense. Most "rigid" armors are flexible and dent and deform quite a bit when struck. They don't spring back to their original shape, but they still convey blunt trauma through them, before they are penetrated.

For every full ​multiple of an armor's BT you take of crushing, cutting, impaling, or piercing damage you suffer 1 HP of injury due to blunt trauma.

BT eliminates the need for the distinction between flexible and rigid armor, as these exist on a spectrum anyway. Most flexible armors have a BT equal to 1/6 to 1/4 of its DR, or 1/2 to 1/3 for most rigid armors. The minimum BT is 1, which means that the armor offers no protection from crushing damage and converts the other forms of damage into crushing. This is appropriate for light mail and thin cloth armor.

I based the BT ratings partly off the NIJ standard, where the deformation a projectile creates upon impact cannot exceed 44mm (1.73 in.). A penetration of 44mm is known to cause broken ribs and internal bleeding and possible death, this must be close to a major wound, which is 5-6 points of damage for an average person with 10 HP. So a BT equal to 1/5 DR means that if an attack does damage equal to the armor's DR, the target will take 5 points of blunt trauma. I know that armor can deform considerably more than this before being penetrated, but the math is not linear anyway, and this is just a rough approximation for playability.

You could even split the BT rating to cover different damage types.

Some Examples:
TL2 Light Mail is DR 6, BT 1
TL4 Medium Plate is DR 12, BT 4
TL8 Assault Vest is DR 15, BT 3
Trauma Plates add +25 DR (semi-ablative), +5 BT (1/5 of DR)
TL10 Combat Hardsuit: DR 75, BT 15

I put up more examples on my webpage, but this idea has not been fully fleshed out or extensively playtested. Any feedback would be welcome.
Can I just check, in the case of assault vest with plates combined DR40 / BT8

a 7.62 doing say 24 damage would not penetrate the DR but would do 3 pts of blunt trauma injury?


I'll be honest I think BABT is only really an serious issue when it hits the right places .

I think l'd keep the usual blunt trauma rules, but I would allow blunt trauma to count as regular Cr injury if it hit the vitals (and get the extra effects of Cr damage on vitals as per Martial Arts)

For me the problem is that every time some one in that armour gets hit by such a bullet they'll take a 3pt blunt trauma injury

I do agree that the current all or nothing flexible vs. rigid distinction doesn't really work (BABT with plates can be an issue with more powerful rounds)

There was a thread last year discussing some of this that might be worth a look

Last edited by Tomsdad; 04-20-2018 at 12:30 AM.
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Old 04-19-2018, 04:10 PM   #3
JazzJedi
 
Join Date: Dec 2014
Default Re: Blunt Trauma

Quote:
Originally Posted by Tomsdad View Post
Can I just check, in the case of assault vest with plates combined DR40 / BT8

a 7.62 doing say 24 damage would not penetrate the DR but would do 3 pts of blunt trauma injury?


I'll be honest I think BABT is only really an serious issue when it hits the right places .

I think l'd keep the usual blunt trauma rules, but I would allow blunt trauma to count Cr and if it hit the vitals (and get the extra effects of Cr damage on vitals as per Martial Arts)

For me the problem is that every time some one in that armour gets hit by such a bullet they'll take a 3pt blunt trauma injury

I do agree that the current all or nothing flexible vs. rigid distinction doesn't really work (BABT with plates can be an issue with more powerful rounds)

There was a thread last year discussing some of this that might be worth a look
You are correct with your math, 24 damage vs. BT 8 would do 3 points of blunt trauma. I also agree with you that location does matter for blunt trauma, and limbs are not as susceptible, but the head is even more susceptible! BABT is definitely an issue even with rigid armor, and plate armor too - why do you think maces work so well against plate armor. It's not because of penetration.
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Old 04-19-2018, 08:02 PM   #4
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: Blunt Trauma

Quote:
Originally Posted by JazzJedi View Post
You are correct with your math, 24 damage vs. BT 8 would do 3 points of blunt trauma. I also agree with you that location does matter for blunt trauma, and limbs are not as susceptible, but the head is even more susceptible! BABT is definitely an issue even with rigid armor, and plate armor too - why do you think maces work so well against plate armor. It's not because of penetration.
Note that non-penetrating head hits are problematic for reasons other than BABT. BABT is defined as injury caused by armor deformation (which is why it's more a problem for soft armor), but it's also possible to suffer acceleration injuries. In theory any part of the body is somewhat vulnerable, but the head combines relatively low mass (making it easy to accelerate) with being unusually vulnerable to acceleration injuries.
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Old 04-20-2018, 12:07 AM   #5
Mercurae
 
Join Date: Aug 2014
Default Re: Blunt Trauma

I really like this idea. I've seen a couple different ways to handle blunt trauma and I'd like to find a simple solution for playability that also handles it somewhat realistically. From what you're describing, I assume any damage above normal DR does it's regular damage type while anything less is always crushing. I think I like that better than the <1.5xDR does cr dam rule; not sure where that came from though, Pyramid maybe?
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Old 04-20-2018, 12:53 AM   #6
Tomsdad
 
Join Date: Jan 2010
Location: Brighton
Default Re: Blunt Trauma

Quote:
Originally Posted by JazzJedi View Post
You are correct with your math, 24 damage vs. BT 8 would do 3 points of blunt trauma. I also agree with you that location does matter for blunt trauma, and limbs are not as susceptible, but the head is even more susceptible! BABT is definitely an issue even with rigid armor, and plate armor too - why do you think maces work so well against plate armor. It's not because of penetration.
Well like vitals the head gets some serious effects if even 1 pt get past the skull so that probably OK, so again I'd say call it an actual Cr injury and apply the location rules (however depending on how you do it it might never come up unless we have really high DR helmets)

On maces and plate, maces were good against plate, but it's more they are good relative to weapons that are particularly bad at plate. Plate was designed to spread the force of concussive impacts and so diffuse it. Which goes to the point about rigid armour that is actually a rigid piece where the body is held within it and not even necessarily directly in contact at all points even with arming garments etc (e.g some cuirasses), compared to rigid plates held in a flexible vest that can move and push against the body in a hard enough impact.



Anthony raises a good point about concussion, there was discussion of it (here towards the end), but again head protection was and is designed with this in mind, padding etc will mitigate it.

However bullets being so light will not impart much momentum when it come to concussion, a 7.62 Nato will have approx 8.3 kg m/s momentum I think. This was also touched on in that first thread I liked in my first post.

Last edited by Tomsdad; 04-20-2018 at 06:24 AM.
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Old 04-20-2018, 01:47 AM   #7
JazzJedi
 
Join Date: Dec 2014
Default Re: Blunt Trauma

Quote:
Originally Posted by Tomsdad View Post
Well like vitals the head gets some serious effects if even 1 pt get past the skull so that probably OK, so again I'd say call it an actual Cr injury and apply the location rules (however depending on how you do it it might never come up unless we have really high DR helmets)

On maces and plate, maces were good against plate, but it's more they are good relative to weapons that are particularly bad at plate. Plate was designed to spread the force of concussive impacts and so diffuse it. Which goes to the point about rigid armour that is actually a rigid piece where the body is held within it and not even necessarily directly in contact at all points even with arming garments etc (e.g some cuirasses), compared to rigid plates held in a flexible vest that can move and push against the body in a hard enough impact.



Anthony raises a good point about concussion, there was discussion of it (here towards the end), but again head protection was designed with this in mind, padding etc will mitigate it.

However bullets being so light will not impart much momentum when it come to concussion, a 7.62 Nato will have approx 8.3 kg m/s momentum I think. This was also touched on in that first thread I liked in my first post.
Thanks for that link. Interesting thread, and they came up with a very similar house rule. Momentum and energy are tough to distinguish from weapon damage, but since it is known that the 7.62 Nato can cause moderate injury (broken ribs and internal bleeding) through a vest and trauma plate. This seems to fit my rule pretty well.
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Old 04-20-2018, 03:37 AM   #8
Tomsdad
 
Join Date: Jan 2010
Location: Brighton
Default Re: Blunt Trauma

Quote:
Originally Posted by JazzJedi View Post
Thanks for that link. Interesting thread, and they came up with a very similar house rule. Momentum and energy are tough to distinguish from weapon damage, but since it is known that the 7.62 Nato can cause moderate injury (broken ribs and internal bleeding) through a vest and trauma plate. This seems to fit my rule pretty well.
Cool, I can't get anything on your link, this one is getting a bit old now so may well have been superseded but it's the one I linked to in the thread I mentioned earlier.

a relevant summary here is I think:

• the BABT injury potential of defeated
high-energy bullets (i.e. 12.7mm calibre)
was significant;
• that of 7.62 mm bullets was largely
dependent on the armour design;
• there was no evidence of significant BABT
injury from 5.56 mm military bullets.


It then goes on to discuss the points about armour design

Last edited by Tomsdad; 04-20-2018 at 06:22 AM.
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Old 04-20-2018, 09:02 AM   #9
tbone
 
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Join Date: Aug 2004
Default Re: Blunt Trauma

Quote:
Originally Posted by JazzJedi View Post
I've been playtesting a hack I made to simulate blunt trauma and thought I would share. For years, I used T-bone's Edge Protection rule, but I found this unsatisfactory for ballistic armor with trauma plates and other rigid armor especially with high DR ultratech armors, such as TL 10 Combat Hardsuit (DR 75) which would convert to DR 60 EP 25. This means that there is no blunt trauma from the first 60 points of damage, which doesn't seem realistic to me.
Hi! Glad to hear that you've been able to make use of the Edge Protection rule to mostly good (?) effect.

With high-DR ultra-tech armor, it's true, the rule leaves characters' rigid armor soaking up 60 (or whatever) points of damage without any ill effect on the wearer (save lots of glorious knockback). That's not an effect of the Edge Protection rule per se; it's an effect of high-DR armor in GURPS (and since the armor is rigid, the EP rule doesn't reduce its όber-DR by much).

That's a bit unsatisfactory to me too, so you may have noticed that the EP rule page addresses the matter in a suggested option. The short version:
If you take a massive wallop to the steel breastplate or ceramic trauma plate or TL10 ultra-plas battle plate... that armor may refuse to crack or deform a bit, but you're still taking a huge wallop. It's just spread over a large area, that's all - something that should certainly lessen the damage, but not protect you completely.

So, the suggestion: Apply a blunt trauma-like rule to all armor. That is, for all damage fully stopped by armor DR, apply 1/5 of that damage (round down) as crushing damage. That's from the armor itself slamming into you.

That suggested option might not deliver quite the effect you want, but for anyone wanting to play around with it, there it is.


Footnote 1: For collisions, GURPS already uses this same rule (i.e., no matter how much DR the armor offers, rigid or flexible, you still take basic hits/5, up to DR/5, as blunt trauma damage). My suggestion only says "Hey, it's probably realistic to apply that to all impacts, not just collisions."

Footnote 2: The suggestion raises a question: If rigid armor allows up to DR/5 basic hits from weapons to get through as blunt trauma damage, then what about flexible armor?

Answer: If you're using the EP rule, there's nothing more to consider; flexible armor is already modeled by low DR, high EP.

If you're using plain GURPS armor (just classic DR, no funny EP business), you can differentiate rigid vs flexible armor by using a different divisor. For example, if rigid armor lets up to DR/5 get through as blunt trauma, flexible armor could let up to DR/3 get through. Or DR/2 or DR/4, if those seem more right. (Which – if I'm reading your post correctly – is what you're suggesting with BT?)


Anyway, that's all in the spirit of "more toys for the hackers". In the end, using the above suggested option may not make a big difference for low-tech armors, but I think it's a welcome way to put a little fear into smug wearers of oh-so-impenetrable high-tech armors.
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Old 04-20-2018, 09:13 AM   #10
JazzJedi
 
Join Date: Dec 2014
Default Re: Blunt Trauma

Quote:
Originally Posted by Tomsdad View Post
Cool, I can't get anything on your link, this one is getting a bit old now so may well have been superseded but it's the one I linked to in the thread I mentioned earlier.

a relevant summary here is I think:

• the BABT injury potential of defeated
high-energy bullets (i.e. 12.7mm calibre)
was significant;
• that of 7.62 mm bullets was largely
dependent on the armour design;
• there was no evidence of significant BABT
injury from 5.56 mm military bullets.


It then goes on to discuss the points about armour design
Thanks for the link and better article. This does throw a wrinkle in my BT numbers for trauma plates. Damage from 12.7mm averages at 49, which means 50 DR is needed to stop it from penetrating. The article mentions that the 12.7mm causes 'significant' BABT, which should be a major wound (6+ damage) from BT. This is still impossible to achieve under the RAW.

The standard vest (DR 15, BT 3) + trauma plate (DR 25, BT 5) will stop a 5.56mm, doing on average 1-2 points of blunt trauma. This is definitely significant. If I adjusted the BT of trauma plates to be 1/3 of DR (DR 25, BT 8), then it would do 1 point except on an extremely lucky hit.

If we take a vest (DR 15, BT 3) and add an extra thick trauma plate (DR 45, BT 15), then a 5.56mm, with average damage of 17, would do no BT on average, while the 12.7mm would do 2.7 points. Is that 'significant' enough?
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