In the South African market and construction industry scissor lifts and MEWPS of all types are becoming more and more popular work tools, due in part to their mobility and relatively small and compact storage space. Properly trained workers need to be certified and know the SOP on its use; a worker can drive it directly to the work area and extend it to the desired height. When finished, they can easily retract and move or be stored for future use. Today, MEWP’s can be found everywhere: retail establishments, manufacturing operations, construction sites and any place that may require access to heights. According SANS, guardrails are considered an acceptable form of fall protection; however, guardrails do not completely eliminate the possibility of a fall from MEWP. Most meet and or exceed the height requirement for guardrails as the only form of protection required (1.067m, +/- 7.62cm), but there still exists the possibility a worker could fall through the space below the mid rails or over the top rail. A competent person, as defined in the OHS act, should evaluate the fall hazard and take corrective measures to eliminate it. One such corrective measure is the use of an approved fall arrest or prevention system. A complete personal fall arrest or prevention harness system will include the anchor point, connector, and body support and in the event of a fall, prompt rescue. Fall arrest\prevention systems are designed to arrest a worker’s fall and reduce the arrest forces on the worker’s body to an acceptable level. However it is not yet and to the best of my knowledge compulsory to wear a fall arrest or prevention system when working from a MEWP. This in my opinion is a concern as depending on the type and mode of deployment or extension of the extendable boom on a extendable boom personnel lifter would a person falling from it not in some cases pull it over, or cause it to be pulled over and capsize, as the shock absorber pad tensions up under load of the person falling exerting an approximate 10 200 KG shock weigh in what I imagine would be an almost jerking effect. This I believe would or may exceed the SWL of the MEWP and be the reason it would capsize and crush persons in its path or trapped beneath it. A deceleration exerting a force 150 times the normal pull of gravity on a body will increase its normal weight 150 times during the time this increase of force acts. Thus, a force of 150 g acting on a man normally weighing 68 kg would increase his apparent weight to 10 200 kg during the force interval. This increase of force and weight would be distributed over, or applied to, his body as pressure in areas of contact dictated by resisting structure (Safety Harness) and possibly the point to which he is attached to the MEWP and the MEWP as a whole itself. It is, of course, obvious that speed, or height of fall, is not in itself injurious. Also a moderate change of velocity, such as occurs after a fall into a fire net or onto an awning or safety harness need not result in injury, but a high rate of change of velocity, such as occurs after a 10 story fall onto concrete, is another matter. Between these two extremes lies important evidence of the human bodies physiologic force tolerance. In using expression “free fall†a fall free of any obstruction other than that encountered at its termination is implied. The word deceleration and its derivative decelerative (Slowing down) are used in preference in describing negative acceleration, etc; “velocity at contactâ€, is preferred to “impact velocityâ€. The force of gravity denoted by the symbol (g) is used as a measure of the force of a positive or a negative acceleration. A deceleration which exerts a force 150 times the normal pull of gravity on a body will increase its normal weight 150 times during the time this increase of force acts. Thus, a force of 150 g acting on a man normally weighing 68 kg would increase his apparent weight to10 200 kg during the force interval (Impact force of 45.3 Kn. This increase of force and weight would be distributed over, or applied to, the attachment point on the MEWP (If wearing Fall arrest equipment (safety harness) and his body as pressure, in areas of contact dictated by resisting structure (Safety Harness) or the ground as the body impacts with it or any obstruction connected during the fall The velocities reached in the following cases of free fall are estimated from the acceleration equation: v = , in which the falling object is accelerated by the force of gravity ((in a vacuum) NB: not normally taken into account for risk assessment purposes) — v being the velocity, g the value of gravity in the acceleration (9.81m [976 cm] per second per second) and s the distance fallen. But if you wish to be pedantic then: Deductions(Reduction of Velocity) in velocity made on account of the resistance of the air (as opposed to in a vacuum) are rather arbitrary and are estimated on the basis of weight, clothing worn and whether the body was observed to be falling head first flat or with a tumbling motion. The estimated forces of deceleration are made from an inversion of the equation for acceleration, v2 = 2 gs, in which s equals the distance in centimeters (30.5) through which a known velocity is decelerated. The resultant expression of decelerative force in Kg’s must be divided by the force of gravity factor (9.81m per second per second) to give the increase times normal gravity. Well now that you can work out just how hard your employees, colleagues and workers may hit the ground, you may be able to convince them that the wearing of a safety harness when working at height from any structure, machine or MEWP is a good idea, or Is it? You be the judge.
Hi Brian, Very good article, and is very descriptive, and really makes it hit home. In a separate forum i have made some comments on Scaffolding and anchor points. As this is the beginning of any life saving FPP, the need to ensure that the anchor point is capable of taking the dynamic load of the number of person attached to such a point. We as HS practitioners often forget that these points should be certified to be able to take the load. In SA we normally just say - hook onto the handrail, but there are handrails and hanrails. Once again - excellent article Regards Shane Lishman CMIOSH
