Why Jumping from a Vehicle is a Bad Idea
Jumping out of a work vehicle. We see people do it from time to time, and we’ve probably done it ourselves more than once. I know I have jumped off the bed of a pickup truck before, simply because it was the easiest (and quickest) way to get down.
The increased risk of spraining an ankle or breaking a leg from jumping is obvious, but what happens to our bodies when we jump down from a vehicle?
The force that our legs must endure when landing a jump can be surprisingly large. It is a bit difficult to accurately calculate this force, but we can use the principle of the conservation of energy as a start.
The Equations
We can start out with defining potential energy of the person about to jump as:
When the person hits the ground the potential energy has all become kinetic (or moving) energy, E, and is calculated from the mass of the individual m, the force of gravity g, and the height h that the individual falls. In this case the mass m times the force of gravity g will equal the weight w of the person in pounds.
To get an estimate of how much force the individual will experience when hitting the ground, we can use the Work-Energy principle:
The average impact force F times the distance traveled while slowing d, equals the change in the kinetic energy of the individual dE. We assume that the person comes to a stop after the jump, so all their kinetic energy will go into their body absorbing the impact, so we can say that dE will equal the E from the first equation.
The distance traveled while slowing, d, will need to be estimated. We can think of this distance as how much the knees and the rest of the joints absorb the impact. This is why if you land from a jump and bend your knees deeply, you end up increasing the amount of time, and distance, the force acts through the legs, which decreases the peak force the legs will experience. In similar fashion this is like landing on a big soft cushion when falling, it uses a long distance to slow the person down and reduce the impact force, cushioning the landing. And this is why if you land a jump with rigid legs, it hurts!
If we combine these two equations, we can get an expression to estimate the total impact force someone will experience when jumping to the ground:
Let’s run a calculation for a 200lb individual jumping from the cab of a dump truck at a height of 4ft. We can assume that by bending the knees several inches during landing, in combination with other shock absorbing features of the human body and footwear, the equivalent distance d we can use for our calculations is 1 ft. Therefore, our calculations become:
This seems incredibly high and almost unbelievable, this is 4 times the person’s weight! Unfortunately, we see high impact multiples like this all the time when using our vehicle Egress Training System. Our Egress Training System measures the force as the person steps (or jumps) down to the Egress Force Plate. We typically see force multiples from 2x – 3x when someone jumps from their vehicle cab, and we have seen closer to 4x when people have jumped from the back of their bed or trailer!
Here is a video of someone jumping from the bed of a truck with the displayed force reading from our Egress Training System. Compare the force reading difference when they jump out versus a controlled egress using the attached ladder. Jumping places 3.3x the force on their body versus a controlled egress. What a difference!
Experiencing these huge forces, day after day, will accelerate the wear and tear on our joints and muscles, increasing the risk of acute and chronic musculoskeletal injury.
The Solution
So how do we encourage vehicle egress that reduces the impact on the human body and reduces the likelihood of an injury? We can verify through our measurements that if an individual uses proper 3 points of control and lowers themselves slowly from the vehicle, the impact force they experience is no greater than their body weight. Proper vehicle egress is comprised of:
· Proper 3 points of control, which means always having 3 contact points with the vehicle at all times during the egress,
· Face the vehicle during the egress; we tend to fall the direction we’re facing and leaning, and a fall into the vehicle is more likely to be recoverable than a fall away from the vehicle,
· Reduce distractions; do not carry anything down with you, and do not look at your phone or other distractions while descending,
· Go slow; take your time and make sure you maintain 3 points of control,
· Secure your footing on the step to the ground; a lot of injuries occur on the final step down to the ground. If you step onto a slippery or uneven surface and release your weight before your foot is securely planted on the ground, it can end in disaster. Make sure your foot is secure and stable on the ground before you let go of your handheld points of contact.
An effective egress training, like our Egress Training System, not only teaches proper egress technique but provides learning insight to change behavior and help employees make safe choices at work and at home.
To learn more about our innovative Egress Training System, check out the Egress Training webpage or contact us.
