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Site life saver

The holy grail of site safety is to find a simple, practical solution that save lives. Margo Cole reports from a site in west London on a device that could do just that.


High on the list of priorities for anyone running a civil engineering site is making sure noone comes into accidental contact with the heavy machines that plough up and down. Even a glancing blow from a piece of construction kit weighing anything upwards of 35t could cause a severe injury.

But construction workers and engineers tend to be fairly complacent - or ignorant - about the dangers of working around the machines, and often stray far too close.

It is something McArdle general manager John Wellard has been determined to address.

“Over the years we’ve recognised that our principal risk - because we’re an earthworks company - is the interface between operatives and plant. It stands out like a sore thumb,” he explains. “We’ve been through a lot of behavioural change programmes, and they worked well enough, but eventually we hit a brick wall. We needed something to force that behaviour change.”

What would be perfect, he thought, would be for site workers to wear some kind of watch or tag that would set an alarm off if they got too close to a piece of plant.

Fast forward a year or so, and that is exactly what McArdle has now got, thanks to a link-up with UK company OnGrade, which has developed the Site Zone proximity warning system.

The earthworks contractor trialled the system last year on its M25 subcontract, and it is just completing work on its first site on which all site personnel and all machines have used Site Zone.

“We can effectively put a bubble around a machine so if it sees a tag it will sound an alarm to warn the operator and the pedestrian”

The system is very simple, and is based on established radio frequency identification (RFID) technology - the same technology that triggers an alarm in a shop if you walk out with the security tag still attached to an item. All site operatives wear a tag with an RFID chip embedded in it, and each piece of plant is fitted with antennas that pick up a signal from the tag if it comes too close, triggering an audible alarm and a warning in the cab.

“We can effectively put a bubble around the machine - a customised zone so if it sees a tag it will sound an alarm to warn the operator and the pedestrian,” explains OnGrade director Gary Escott.

Unlike a reversing alarm, which goes off when a vehicle gets close to any object, the Site Zone alarm only sounds when someone wearing one of the tags is in close proximity - effectively warning that someone is close enough to be in danger. As McArdle hoped, the system has prompted the behavioural change it was looking for, as no-one wants to be responsible for setting the alarm off.

The firm is just coming to the end of an earthworks and landscaping contract on the outskirts of Heathrow Airport as subcontractor to Vinci. At the start of the job it fitted Site Zone to all eight items of heavy plant it was going to use - dumpers, articulated dump trucks, dozers and excavators - and issued tags to the 20 people working on the site.

Everyone gets their own tag, and they are checked at the start of each day to ensure they are not running out of power.


Being able to link each person to a specific tag is an important component of the behavioural change element of the system as, in addition to sounding an alarm, any breach of the “bubble” around the machine is logged using telematics. Every breach appears on a website, so the site manager can see who has breached the safe zone, and which machine they came too close to.

“It may seem a bit heavy handed, but it really is a good way of managing it,” says Escott.

“The number of breaches comes down very quickly, and if you find you’re getting a hot spot you can change your way of working.”

Wellard agrees. “It’s certainly not an ‘install and leave’ system,” he says.

“You will get breaches, and you need to look at those, see what’s causing them and go out and resolve those issues. It forces you to look at what you’re doing.”

For example, he says: “Quite often you need to talk to the driver or approach them, but the safe way to do that is if the item of plant is unoperational.”

As a result, McArdle has linked the system to the dead man’s handle mechanism on every machine, so that the only way you can get close enough to talk to a machine operator without the alarm going off is if they have cut the engine.

“This isn’t a replacement for safe systems of work,” says Wellard. “The fact remains the same that people shouldn’t be getting close to pieces of plant. This is another line of defence - more or less the last line of defence.”

“Ultimately we want to use these tags as identity cards so they can be trigger a gate to open or be used for access control”

For most of the contract period on the recent project near Heathrow, the “bubble” around the machine was set so the alarm would sound if someone was within 8m of a machine. When it came to working in a more confined area, with machines working very close to each other, it was adjusted to 5m.

“At that distance, with a machine coming up in front of you, that feels dangerous,” says Wellard. “The alarm is there to tell you that you are in imminent danger of being seriously hurt and you should get out now.”

McArdle has worked very closely with OnGrade to develop the system, and is now so convinced about its benefits that it plans roll Site Zone out on all of its jobs and all its pieces of plant.

“Our intent from the beginning when we first found out about the system was to have it across the whole company. We have just been trying to make sure it was fit for purpose,” says Wellard.

“The restriction to running it as much as we would like is our clients. For many jobs we’re the earthworks subcontractor. We plan to have our own operatives protected around our own pieces of plant, but we need main contractor buy in because they will have engineers going in, and our operators will be expecting alarms to go off if they get too close.”

Wellard knows the decision to use the system across all of its plant and site workers has financial implications, but believes the investment is worthwhile. “For a contractor that’s willing to invest in this sort of technology, it adds to the hourly cost of running a piece of plant,” he says.


“We know that puts us at a disadvantage, but we’re going to stick to our guns, and we think it’s the right way to go.” As McArdle project manager Jason Goatcher puts it: “You can’t put a price on a man’s life.”

The firm is also looking at other things it can do with the tags. “Ultimately we want these tags to be their identity cards, so they could be used to trigger a gate to open or for access control, says Wellard. “It then becomes part of the control of who’s been inducted, what time they arrived on site and what time they left.”

OnGrade is also continuing to develop the system, and is set to produce tags that vibrate when the safe zone is breached, in addition to the alarm sounding.

It has also produced a lowcost version - aimed at the hire market - that includes antennas that can be magnetically mounted and powered by a machine’s on board auxiliary power.

  • Site Zone will be demonstrated at the CETA Technology Showcase at Newbury Racecourse on 3 and 4 October.

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