Post Sun Oct 25, 2015 12:50 pm

Nerf Rocket Cracked a HUMVEE Window!

Image

Video: https://youtu.be/GN5yIXOoiNQ

A Nerf rocket cracked Amped Airsoft's HUMVEE windshield at Irene 2015. Although the windshield was not the bulletproof model, the impact still seemed substantial and could have caused serious injury if hitting a player. Therefore, an investigation of the rules and their enforcement regarding use of large caliber projectiles in both Airsoft and paintball games is warranted. The aims of this essay are: 1) Raise awareness of blunt trauma prevention in Airsoft or Paintball, 2) Dispel the wrong notion that a soft and spongy projectile is safe at whatever velocity. In contrast, A hard but light projectile can be safely used in games with proper regulations and protection.

From what I can gather from the Web, the common 230 fps limit for Nerf rockets was based on anecdotes. There are many scientific studies on kinetic non-lethal weapons, and we should consider them when making rules. Kinetic non-lethal weapon studies have shown that although the materials of the projectiles affect their blunt trauma injury potentials, the COMBINATION of the projectile mass and its impact velocity and impact area has stronger correlations with the level of injury induced. [Lyon, 1999; Koene, 2008] In this case, the combination of the mass of the Nerf rocket and its impact velocity and impact area may be too much for the HUMVEE window. Since Nerf rockets have been used without similar incidence in the past, their mass and impact area are likely not an issue. The only possibility left is that it was flying too fast and the launcher was shooting too hot.

In non-lethal communities, 44 mm indentation on ballistic clay is commonly used as the failure criterion (i.e. lethal potential). The ballistic clay is difficult to prepare, but it is possible to use energy density (energy per impact area; J/cm^2) to estimate the indention on ballistic clay. [Lyon, 1999] I will present the estimated indention on ballistic clay for a 32 gram 2-in Nerf Rocket shot at 230 fps (maximal velocity limit for Nerf rocket in most events) and 150 fps, a 3.5 gram 0.68-in paintball shot at 230 fps (typical limit), and a 26 gram TAGinn projectile shot at 150 fps. Given a 32 gram 2-in Nerf rocket fired at 230 fps, the energy produced is 78.6 J, and the energy density is 78.6 / (pi * (2.54^2)) = 3.88 J/cm^2. The estimated indentation is 12 mm. Given a 32 gram 2-in Nerf rocket fired at 150 fps, the energy produced is 33.4 J, and the energy density is 33.4 / (pi * (2.54^2)) = 1.6 J/cm^2. The estimated indentation is 2 mm. Given a 3.5 g 0.68-in paintball fired at 230 fps, the energy produced is 8.6 J and the energy density is 8.6 / (pi * (0.86^2)) = 3.7 J/cm^2. The estimated indentation is 10 mm. Given a 26 gm TAG projectile fired at 150 fps with 400 psi of CO2, the energy produced is 26 J, and the energy density is 26 / (pi * (1.85^2)) = 2.56 J/cm^2. The estimated indentation is 6 mm. They are all below lethal threshold, and given the indentation caused by Nerf rocket shot at 230 fps is similar to that by paintball, it may seem the 230 fps limit is acceptable. However, this model assumed that the projectiles were hitting the torso area. The torso area can usually take more punishment because it contains great amount of muscle and fat tissues, while the head area is more susceptible to injury because of its thin surrounding soft tissues. Studies have shown that facial bone and skull facture can occur above 40 J.[Clemedson, 1968; Schneider, 1972] Since the head area contains many vital organs, its protection must be considered when making rules for Airsoft or paintball games. Given 40 J as the maximal acceptable energy for Airsoft or paintball projectiles and a 32 gram 2-in Nerf rocket, the maximal acceptable velocity is SQRT (40 * 2 / 0.032) = 50 m/s (164 fps).

Below is my recommendation based on my literature review:

    1. Large caliber projectiles for Airsoft or paintball games should have maximal energy of less than 40 J. For Nerf rockets, the maximal velocity should then be less than 164 fps. For TAGinn projectiles (Pecker and Paladin), the maximal velocity should be less than 180 fps. But for the sake of simplicity and additional protection, 150 fps should be the maximal velocity for all projectiles.
    2. Large caliber projectiles for Airsoft or paintball games should also have maximal energy density of less than 3.7 J/cm^2. Nerf rockets and TAGinn projectiles should already meet this criteria after tuning down to 150 fps.
    3. Minimal engagement distance (M.E.D.) for large caliber projectiles should be 50 feet for additional protection as well as realism - typical arming distances for real 40-mm grenades range from 46 to 92 feet.
    4. Referees should carry chronographs to spot-check launchers on the field just as many have been doing for Airsoft guns or paintball markers.
    5. The hardness of the projectiles does not have as much effect on safety as previously thought. TAGinn dummy projectiles (Pecker) should be allowed in games, and if sites allow, the chalk ones (Paladin) as well.

REF:

    1. Lyon, D.H., Bir, C.A., Dubay, D. “Inury Evaluation Techniques for Non Lethal, Kinetic Energy Munitions”, Army Research Laboratory, Aberdeen Proving Ground, Report # ART-TR-1868, Jan 1999.
    2. Koene, B., Id-Boufker, F., Papy, A. “Kinetic Non-Lethal Weapons” in “Netherlands Annual Review of Military Studies”, 2008
    3. Clemedson, C., Hellstrom, G., Lindgren, S. “The Relative Tolerance of the Head, Thorax, and Abdomen to Blunt Trauma”, Annals New York Academy of Sciences, Vol. 152, 1968.
    4. Schneider, D.C., Nahum, A.M. “Impact Studies of Facial Bones and Skull”, Proceddings of the 16th Stapp Car Crash Conference, November 1972