By Chris Rufert.
There are some in our industry that still believe cutting a stored gas inflation cylinder of an airbag assembly during a vehicle extrication event is a sound practice. The question is why we would maintain this line of thinking? So I want to try to spell out some technical and some not so technical aspects of the idea of cutting a pressurized stored gas inflation. This is what we know to be true:
On the small end a stored gas inflation cylinder is approximately 1 ¼ inches X 9 inches. These assemblies contain approximately 3000psi or greater. Doing some simple math, we know that there is close to 1.5 cubic feet (ft³) of compressed gas in these cylinders. We know that the cylinder must inflate an entire airbag in milliseconds. What happens when one of these pressurized vessels has an uncontrolled release? What kind of energy is produced? Based on a study by the U.S. Department of Energy of common household pressurized items, a pressurized cylinder with an internal volume of 1.42 ft³ pressurized to 2500 psi holds a stored energy of 982,500 lbf-ft (pound force foot, measuring force as torque). At only 1000 lbf-ft shrapnel debris can be produced out to 13ft. Ear drums can rupture at 12 inches away and lung rupture can occur within five inches. Compare this data to a typical CO2 Cartridge (12 gram) used in air guns with a stored potential energy of 650 lbf-ft. Additional data demonstrates that a mere 1 lbf-ft blast wave will produce shrapnel out to 16 inches and ear drum ruptures as close as 1.2 inches, yet none of us would consider cutting a typical CO2 cartridge with our extrication cutters for fun.
Understand that a lung hemorrhage is not a realistic injury due to the fact that being in this close proximity, coupled with the need of the shock wave to penetrate through skin, muscle and bone, creates a near impossible scenario. Furthermore, blast injuries are conducive to the exposure of the shock wave pressure spike (lbf-ft) over a period of time (milliseconds). However, the impact or lack of impact can be increased by confining the blast, or decreased by shielding from the blast. This is directly related to the relationship of the rescuer outside of the vehicle and the patient inside the vehicle. To make matters worse the danger is increasing. Currently, vehicles are coming out that have stored gas inflation cylinders pressurized to 10,000psi. These cylinders are approximately the size of a children’s lunch thermos; meaning that they have the potential to contain approximately 17ft³ of compressed gas. The pressure spike is directly related to the volume of gas, and the pressure exerted over the surface of the cylinder wall. So what kind of potential blast could a rupture of this type of cylinder produce? Picture cutting a SCUBA pony cylinder or an SCBA cylinder with your cutters; the potential hazards far outweighs any possible benefit.
What if we look at the cutting of a stored gas inflation cylinder from a best practice methodology? You do not need to go very far in an internet search to find that no individuals in the fire rescue service are advocating the cutting of these cylinders. Furthermore, every vehicle manufacture and MSDS sheet make definitive cautionary statements regarding the cutting of the stored gas inflators. Some have even gone so far as to deter responders from cutting them even after they have been deployed and pose no threat just so responder are not in the practice of cutting the cylinders. What this means to the responder is that if you decide that cutting a stored gas inflation cylinder will be your method of attack, and doing so harms the patient or personnel on the scene, you will be negligent and civilly liable for any injuries sustained.
Below are three videos of non-scientific demonstrations of people cutting deployment cylinders. In one video you will notice that only thing that happened is that the curtain bag deployed. However, also note that the cutter rotated into the cylinder and likely fractured the link that holds the gas in the cylinder before it fractured the sidewall of the pressure vessel. The evidence is undeniable that the practice of cutting the stored gas inflation cylinder is not in anyone’s best interest and doing so is nothing more than a game of Russian roulette.
About Chris Rufert:
Chris Rufert is a 23 year veteran of the fire rescue service. His introductory training began in 1990 while serving in the U.S. Army in Korea. In 1991, he was deployed to Operation Desert Storm where upon returning was stationed at Ft. Bragg, NC and became involved as a volunteer firefighter in Cumberland County. Having served both volunteer and career fire departments, he has held the positions of Firefighter, Captain and Training Officer. Since 2000, he has served with the Charlotte Fire Department in North Carolina. His current position is Fire Captain, serving on Ladder 29, A Division. He is a North Carolina Fire/Rescue Instructor specializing in Forcible Entry topics, Vehicle, Rope and Confined Space Rescue. He holds an A.S. in Fire Protection Technology from Central Piedmont Community College and a B.A. in Homeland Security from American Military University. He can be contacted through E-Mail at firstname.lastname@example.org
“Let no one say that their training failed them”