Brake Testing For Rubber-tyred Vehicles Operating in Quarries, Open Cast Coal Sites and Mines (2nd Edition)

Abstract

In the past, brake testing of rubber-tyred vehicles operating in quarries, opencast coal sites, mines and similar environments, comprised ‘simple’ stopping distance tests, typically carried out at daily or weekly intervals. More recently, many operators of such plant have progressed to using a brake testing method that employs electronic instrumentation, as a means of determining the ‘brake ratio’ of a vehicle. This is because instrumented testing gives more accurate results. Accordingly, the time between performing these instrumented tests has increased to monthly, or even 3-monthly, intervals. For both simple and instrumented test methods, international standard ISO 3450 is often (wrongly) used as the guide to acceptable brake performance testing regimes. The ISO standard contains formulae that enable either a stopping distance or a brake ratio to be calculated (depending on which test method is used). However, these calculated values are minimum levels of braking ability necessary for a vehicle to be placed on the market. That is, the ISO standard is a minimum standard for manufacture, not a maintenance standard. To put this into context, it is likely that any ‘modern’ vehicle will have levels of braking performance approaching twice these minimum ISO values. In using these ISO values as routine test pass or fail criteria, organisations may be indirectly accepting that brakes on modern vehicles can deteriorate by up to 50 per cent before their operators become concerned with braking ability. In addition, test conditions on site (particularly speed and gradient) may be much less onerous than those used in ISO 3450, which produces low test results. The overall outcome of this may be a ‘poor’ brake test result, but one that exceeds a low level pass criterion and is not, therefore, seen as a test failure. Another common problem with some brake testing regimes is that they do not readily correlate to site operating conditions; in particular to gradients, but also to vehicle speed and load. The law requires organisations to ‘ensure’ that work equipment is suitable (safe) for the conditions of use it will encounter. This means being able to demonstrate that vehicle braking capabilities are adequate for actual site operating gradients, speeds and loads. Naturally therefore, any testing regime should accurately take account of the site conditions which the vehicle will be exposed to. In order to address these shortcomings regarding brake testing of rubber-tyred vehicles, this guide explains the brake ratio method of brake testing. A step-by-step guide on how to correlate braking performance with actual site conditions and how to design and put in place a suitable brake test regime is preceded by several discussion chapters. The written report was compiled in collaboration with the Health & Safety Executive (HSE), the Off-highway Plant and Equipment Research Centre (OPERC) and the Mineral Products Qualifications Council (MPQC – formerly EPIC).