IPAF: Assess ground conditions when using powered access equipment
Users consistently underestimate the weight of booms and scissors. This can lead to serious accidents. Mobile elevating work platforms (MEWPs) are stable and robust machines that, in the hands of properly trained and familiarised operators, offer a safe and effective way to work at height. However, incorrect setup can cause instability and lead to tip-overs. This is often the result of inadequate assessment of ground conditions, insufficient ground support, poor spreader plate selection or incor
In an industry survey, respondents were asked, “Should the use of outrigger mats be made mandatory on cranes and lifts?” Over 81% (787) of the respondents said yes and just under 19% (179) said no. When asked, “Do you offer outrigger mats on all self-drive crane and aerial rentals?”, just over half of the respondents (54%, 98) said yes and 46% (84) said no. These figures demonstrate that there is certainly scope for improvement in the access industry that relies on safety and best practice.
Ground conditions must be assessed before travelling, using or setting up a MEWP on any surface. Tools have been developed to drum home this message about ground conditions and spreader plates. There is a technical guidance document from IPAF on assessing ground conditions (see the Publications/Technical Guidance section of www.ipaf.org). This document also lists site categories that are likely to present hazards and that need to be considered, such as Greenfield sites, beaches, filled construction sites (Brownfield sites), paved areas, uncompacted fill, proximity to excavations, underground services, and floors, cellars and basements. IPAF’s “Spread the load” campaign clearly states that: Spreader plates should always be used with boom-type MEWPs when fully supported on their outriggers. Spreader plates should be used with all other MEWPs that have outriggers unless a risk assessment indicates they are not necessary. Here are some core safety guidelines to note:
Know the weight of machines
At CONEXPO-CON/AGG last year, demonstrations were run at the IPAF Lift Safety Zone asking visitors to guess the weight of a typical 60-foot (18-metre) boom as it drove onto axle weighing scales. Guesses ranged from 4,000 to 50,000 lb (1,814 to 22,680 kg), with the majority being 50% lower than the actual weight of 22,500 lb (10,206 kg). This suggests that most people tend to underestimate the actual weight of the machine, which could be potentially dangerous as the ground support may not hold up to the actual weight.
Be aware of machine point loadings and ground load-bearing capacities
As a machine moves into different configurations, the loads may be concentrated on one wheel or outrigger, sometimes up to 80% of the machine’s gross weight.
As an indication of relative bearing pressures, a car tyre exerts a pressure of approximately 2.4 bar (35 lb/in², 2.46 kg/cm²) whereas a typical MEWP outrigger without a spreader plate may well generate pressure in excess of 13.8 bar (200 lb/in², 14.06 kg/cm²). Looking at the above will lead you to ask: But what are we measuring and what are the units of measurement? A significant problem is that manufacturers currently use a variety of units of measurement. A look across machine operating manuals will throw up terms like maximum wheel pressure, maximum stabiliser ground pressure, maximum stabiliser plate ground pressure, surface pressure, outrigger point loadings. Add to that an alphabet soup of units such as psi, N/cm2, daN, dyne, KPa and it is easy to see why users might be confused.
To bring clarity, IPAF has created a “ready reckoner” conversion tool that enables users to quickly understand the weights and loadings in question. By entering the weights of machines and identifying the different soil types, users can then identify the suitable size and specification of spreader plates to be deployed. Spreader plates should have sufficient size, stiffness and strength to spread the load over the required area. The conversion tool can be found at www.ipaf.org/spreaders
