Nail projectiles propelled by a mason's lacing cord: an experimental approach.

The recent clinical observation of two unintentional penetrating ocular and cerebral injuries due to 90-mm construction nails gave occasion to an experimental study to check the alleged trauma mechanism for plausibility. Both casualties reported that they had attached a mason's lacing cord to the masonry using a nail as anchoring when suddenly the nail was yanked from its moorings and propelled like a missile by the overstretched lacing cord. As to the best of the authors' knowledge, this mechanism of injury has not yet been reported in any of the literature; it was the aim to find an experimental approach to review the plausibility of the alleged sequence of events leading to the accidents. The tensile strength at break and strain at break of different mason's lacing cords (diameter of 1 and 2 mm) were measured according to DIN EN ISO 2062 by using a tensile testing machine. Based on the maximum spring energy of the lacing cords, which was determined 174.9 J for the 1-mm cord (length 10 m) and 747.4 J for the 2-mm cord (length 10 m), the maximum possible velocity of the nails as projectiles was calculated to be 243.5 m/s for the 1-mm cord and 503.4 m/s for the 2-mm cord. The critical elongation a cord of a certain length has to be stretched to deliver enough kinetic energy to a 90-mm nail to surpass the threshold velocity for skin penetration, which was investigated by Sellier (1977) to be approximately 18 m/s, was also calculated. To conclude, the energy delivered by the cords is high enough to surpass the rather low threshold velocity of nails. The details of how these accidents occurred, which seemed questionable at first, can be reasonably explained by trauma biomechanics.