This is the most important point regarding the issue of worker weight, but we need to understand what happens during a fall.
When any body falls, it accelerates and gains energy. Depending on how this body is stopped, this energy can be dissipated or distributed in a way that can injure the worker.
Let’s draw a parallel for the sake of understanding. Imagine yourself inside a car at 60 km/h. In a first situation, when you step on the brake, the car will move for a certain space until it comes to a complete halt. In this way, what will be reflected on the people in the car will only be a slight force projecting them forward from the seat.
In a second situation, if we attach a very long steel cable to the rear axle and start moving. At the moment this cable stretches, the period between braking and displacement is almost zero, similar to what happens when you hit a wall. Everything inside the car will be violently thrown forward.
This mechanics is what happens when we have a fall. We are the cars and our organs are the people inside the car, moving as a result of deceleration.
The function of the harness is to create connection points on the worker’s body and distribute the impact through these points along the body. This impact is directly linked to the energy absorption system that is used during the work.
If we use a lanyard (safety cable that connects the worker to the structure) that does not stretch, it will play the role of a steel cable, i.e., the worker will fall and the impact will be very great. To put a brake on the system we have to include an energy absorber that in case of a fall will open and increase the time interval and braking space.
The test standards test the products under the worst conditions: a factor 2 fall means a fall with twice the length of the lanyard used and a mass of 100 kg (see images below).
image_mechanics-of-a-fall-and-its-risks
If a worker weighing more than 100 kg is in a critical fall situation (factor 2), this fall will generate more energy. This implies that the belt withstanding a static force of 1,500 kgf (according to the standard test) will withstand the impact, but the worker will absorb most of this remaining energy generated by the sudden deceleration, which may cause injuries, even though the absorber will reduce the energies to less than 6 kN.
The solution in this case is not to expose the worker to critical fall conditions. Whenever possible the Lanyard connection point should be above the worker. Not only for people over 100 kg, but for everyone. The smaller the displacement, the less energy is generated.
However, the human body supports an average of 12 kN (kilonewton) of impact distributed along the body. Even so, in every test, according to the NBRs, the fall arrest equipment (lanyard, fall arrest) must not exceed the braking force value above 6 kN, to ensure the physical integrity of the worker.
The Brazilian technical standards of ABNT on safety equipment for fall protection have incorporated this same standard of 6 kN. This means that Personal Protecton Equipment for Work at Height can only get the INMETRO certification and the Approval Certificate (CA) from the Labor Ministry, ifsuspens tested in a laboratory to prove that it can retain the fall of a person generating on his/her body a maximum of 6 kN.
Risks after a fall
Suspension Syndrome
A worker can fall when he loses consciousness or lose it when he falls. In both cases, if he is equipped with a fall protection system, he will remain suspended by the Safety Harness until help arrives. The period during which the worker remains suspended without consciousness is called suspension syndrome.
Risk
Recent scientific studies prove that suspension syndrome, even for short periods of time, can trigger serious physiological disorders due to the compression of the arteries and consequently blood circulation problems. These disorders can lead to serious injuries or even death, if rescue is not performed quickly and efficiently.
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