Feature Safety Clear the way for safe inspection


Inspecting energised equipment puts workers at risk of arc flash injuries, but a solution for carrying out inspection without having to remove protective panels is now available, explains David Hinds, EMEA sales manager, IRISS UK


hermally inspecting energised equipment helps to detect electric faults before they become failures. But, while there are many safety regulations in place, the inspection process traditionally involves removing protective panels – which puts workers at risk of arc flash injury. A solution, however, is available through the installation of infrared windows, which means the inspec- tion can be carried out efficiently with the energised system enclosed behind a closed door.


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In fact the installation of IRISS polymer windows at a steel mill not only improved safety but it also boosted productivity. The mill was able to reinvest cost savings in its electrical maintenance programme to minimise unscheduled downtime and protect critical assets.


What is the risk? Arc flash is a short circuit through the air that creates an explosion equal to that caused by up to three sticks of dynamite. Most incidents are triggered by human interaction so the blast occurs in close proximity to workers – burn injuries, sadly, are very common. For some, they are minor, but for others the injuries can be life changing or even fatal. In the US, where employers’ arc flash responsibility is already enshrined in law, the statistics are still sobering. An arc flash incident is reported every 18 minutes. From these, roughly 20 people per day sustain arc-induced burns and five to ten workers suffer incurable third-degree burns over more than half their body. On average, more than one worker each day is the victim of an arc flash fatality. All serious workplace injuries are reportable in Europe, but arc flash isn’t a specific category. These are burns injuries but, based on the US model, arc flash has to be a significant contributor to health and safety statistics. An arc flash can be triggered by drop- ping tools or panels, making accidental contact with energised parts or by changing the state of the equipment. It usually starts as a phase-to-ground short circuit. This ‘bolted fault’ is one bridged by an object – a wrench, for example, with limited current carrying potential. However, when the initial arc vapourises the copper conductor it


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produces a small hyper-conductive cloud of copper plasma and ionized gases. This forms a bridge, changing the nature of the short to phase-to-phase. It is this ‘unbolted fault’ that grows in intensity, producing a blinding flash along with ultra high temperatures. The explosion feeds on itself and the heat converts all materials in the vicinity to plasma. The copper conduc- tor expands 67,000 times its initial size in a fraction of a second – creating the pressure wave that rips apart switchgear and sends molten shrapnel towards anything in its path.


Preventing injuries


Arc flash can hit anyone who is physi- cally exposed to an energised system and, although workplace PPE may lessen injury, the forces involved far outweigh its ability to prevent serious or even fatal consequences.


This is precisely what happened at a steel mill which had long established preventative maintenance and condi- tion monitoring programmes and a highly safety conscious culture. One of its electrical maintenance engineers was injured in an arc flash incident after mishandling a cover while refitting it to an energised panel, resulting in all energized work being immediately stopped. This left critical assets unchecked and production conti- nuity at risk, so the mill’s management commissioned an in-house review. The first step was an arc flash hazard analy- sis to ascertain the actual arc ratings to which staff were exposed while com- pleting energized maintenance tasks. Results showed that the higher expo- sure levels were generally found in the


Using IR windows, live IR and ultrasound inspection of critical assets can be completed safely by one person while the systems are


in-cycle and under full load conditions


mill’s 480V switchgear, which were not what they expected to see. Some were found to be outside the 40 cal (type 4) PPE levels that they had on-site to com- plete the routine maintenance tasks. A survey carried out by the International Electrical Testing Association (NETA) in 2007 indicated that 22% of service-aged circuit break- ers had some type of malfunction and 10.5% did not operate at all during maintenance testing. These findings concerned the mill as it knew its breaker maintenance programme was not up to scratch. In turn, this threw into question the validity of the arc flash hazard analysis on which the calculated levels depended on the breakers open- ing within the design specification outlined by the manufacturer. It was therefore decided to instigate a two-stage plan, with the first step being to reinstate an aggressive breaker maintenance programme and ensure that all breakers met the opening times detailed by the equipment manufac- turers. The switchgear circuits that were found to have very high arc flash levels were to be fitted with devices to increase the breaker clearing times and reduce the arc flash levels.


The next step was to recommence condition-based maintenance but this time with simultaneous infrared and ultrasound inspection via IRISS infrared and ultrasound ports fitted to the panels on critical assets. This would allow work to be completed by one inspector under full load condi- tions with the switchgear guarded and enclosed.


An electrical distribution system review determined where IR windows and ultrasound ports needed to be fitted. They ranged from 120V distribu- tion board covers on critical breakers to 13.8kV primary switches and trans- former cable compartments.


The results


After looking into the IR windows available, the CAP Series from IRISS was selected. These are a further devel- opment from the company’s VPFR series of impact resistant, industrial- grade infrared windows. The transmis- sive polymer lens material that IRISS uses in this patented range of products can be cut to virtually any shape or size – meaning infrared windows no longer need to be round.


In addition, unlike a crystal that becomes too fragile beyond 4in diam- eter, the IRISS polymer poses no such constraint, allowing the company to introduce its Custom Application


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