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Cascade To Disaster

Apr 23, 2014 fleet, maintenance, trucks

Cascade To Disaster

Dave Scott  

‘Cascade’ is well-known in medical terms - blood clotting involves a biochemical cascade. Most commonly ‘cascade’ is used in association with water. Any major failure in road transport is preceded by a cascade of events, defined as ‘something arranged or occurring in a series or in a succession of stages so that each stage derives from or acts upon the product of the preceding’. This term (cascade of events) is very aptly used in Michael Crichton’s gripping novel ‘Airframe’, a must read for any frequent flyer. Root-Cause Analysis is a highly used forensic discipline that relies on detailed examination of an event cascade that exposes the basic and initial real reason for the final incident which we are so quick to blame.

All too often a serious road incident is blamed on apparent ‘tyre failure’. This is pure escapism because the reason for tyre malfunction has a long trail of events that lead up to catastrophic failure – a cascade of events. And far too often transport operational staff stands in the midst of an event cascade, totally unaware of what they are looking at.

A missing tyre valve cap allows road grit to jam the valve when the tyre is checked for pressure. This starts a slow leak that leads to a tyre run-flat at the end of the day with many consequences. And it’s a multiple snake-head of outcomes that bites the business, some of which are not accounted for, such as increased fuel consumption, downtime and driver overtime claims. The direct expenses, providing the run-flat did not catch fire, are invoiced for travel and replacement with new tyre. Now if every tyre is missing a valve cap, as witnessed recently in a 300-vehicle fleet, the cascade of events increases proportionately – the incidents and losses just multiply.

A wheel hub is a safety-critical axle part and must be inspected every day for any traces of impending failure. So what can be the indicators on a wheel hub that events are occurring? Here are a few pointers from George Hartman, Sales Manager – Key Accounts, at BPW Axles (Pty) Ltd:
Lubricant seepage means the bearings are running out of oil/grease – any wheel hub leak must be treated with urgency.

Blistered paint on the hub indicates severe over-heating. Is the bearing failure imminent and due to the wrong lubricant being applied? Has wheel hub overheating occurred due to heat transference from the brakes – in the case of trailers where trailer brakes have been excessively and independently applied through a trailer hand control valve?

It may seem obvious, but a missing hub-cap must ‘stop-the-bus’. A missing hub-cap means severe bearing contamination and bleeding of whatever lubricant remains to prevent wheel hub seizure. A hub-cap on a BPW axle requires 800Nm torque in fastening the cap: so how does such a hub-cap go missing – it doesn’t just fall off?

How is a wheel hub fault reported? Is it just a tick system in among a long list that is too easily glossed over? Does the truck driver have the power to refuse a mission if the wheel hub-cap is missing? Or threatened with dismissal, will the driver be ordered onto the road regardless of the consequences?Is the driver trained to know what he/she is looking at when checking wheel hubs every day – not just what to look for but why?

And then there is the simple ‘touch-test’. Hartman comments: “Brakes will get hot and there is always heat transference to the rim. When a driver stops it’s a simple check to hold one’s hand near the rim and feel the heat – any rim that is excessively hot in comparison to the standard heat emissions of other rims on the truck can be identified as where a serious problem is developing”. The same procedure can be adopted for tyres; a tyre that is failing generates massive heat and the touch-test is a pre-warning inside the cascade of events.

Tracking back on lost reaction time is always significant. We can avoid accidents if we react in time. While speed is the prime choice for reducing reaction time, the contributory factors rapidly mount up – too few hours between bottle and throttle, too many hours behind the wheel without a break, a windscreen washer that does not work and a dirty road in wet conditions, no mud flaps (spray suppression) on the vehicle in front and the overwhelming desire to overtake despite the poor visibility all added to a badly maintained engine with poor power output/acceleration and the recipe of cascading events combines in a bad incident.

When a gas tanker explodes and creates a swathe of destruction within a massive radius, where did the problem really start? Did the cascade of events start yesterday, a week earlier or the year before? This applies equally well to automotive warranty claims and only brutal truth can expose the cascade.

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