Case Studies

Power to the People
Fit for purpose garments protect workers from deadly flashover.

Electric arc flash or electrical flashover is one of the most deadly and least understood hazards of electricity and it is prevalent in most industries. Whilst no records are held specifically for arc flash incidents, in 2010/11, in the UK, there were 394 accidents caused by contact with electricity or electrical discharge[i]. The outcome of an arc flash can be disastrous and whilst legislation requires businesses to perform risk assessments for all work activities, this is often overlooked because most people are unsure how to assess and manage this hazard effectively.

 

With over 2,000 employees working in an area with large volumes of electricity assets and directly at risk of an electric arc flash, Northern Powergrid, a UK distribution business, recognised the need to further enhance the safety of its workforce. To both minimise the risk of arc flash and protect against residual risks, Northern Powergrid used the combined expertise of DuPont and its value chain partners, J&K Ross (UK distributor) and Dale Techniche (Garment Manufacturer) to provide a solution to this dangerous hazard.

 

A high-risk environment
Northern Powergrid constructs, maintains, repairs and replaces assets for distribution across the North East and Yorkshire region to 3.9 million customers. Its network consists of more than 61,000 substations, has around 30,000 kilometres of overhead line and almost 67,000 kilometres of underground cables. The network has a connected transformer capacity of over 38,000 MVA that operates at voltage ranges from 132 kV down to 240 volts.

 

Electric arc flash is usually caused by inadvertent contact between an energised conductor, such as a bus bar or wire, with another conductor or an earthed surface. The resulting short circuit current will melt the conductors, ionise the air and create a conducting plasma fireball with temperatures in the core of the arc that can reach upwards of 20,000 degrees centigrade causing severe injury and even death. These injuries can include external burns to the skin, internal burns from inhaling hot gasses and vaporised metal, hearing damage, eye damage (such as blindness from the ultraviolet light of the flash) as well as many other devastating injuries.


Assessing the risk

A complex risk assessment was carried out by electrical consultant Mike Frain from Electrical Safety UK Ltd over a four month period. The process met European Legislation (80/391/EE) requiring employers to perform a risk assessment on tasks and was framed by the DuPont 4 P approach. This approach recommends that risk assessments should be framed by the steps predict, prevent, protect against and results published. The risk assessment looked at worse case scenarios, taking photos of all the key jobs at risk and measuring the distance between a potential arc and a workers body in different positions. The measurements were collated into a report that evaluated the energy levels, arc flash risks and highlighted areas where there was opportunity to improve.

 

Alongside the need for some re-engineering and re-modelling of the site, the feedback highlighted that the garments worn at the time by Northern Powergrid employees had a poor level of wearer acceptance due to an uncomfortable design. It also highlighted that the garments were not simple or flexible in their use, with many garments not compatible with each other. There was also an uncertainty on how to match the PPE with hazards in relation to arc flash and whether the existing FR clothing provided an adequate Arc Thermal Protective Value (ATPV). In addition to keeping employees safe, having a professional image and a corporate brand was key. The new designs had to not only adhere to the corporate identity of Northern Powergrid, but also had to be adapted to the working environment of the employees so that the highest degree of usability and comfort could be provided.

 

Collaborating to develop a new solution

DuPont identified technical fabrics and solutions that adhere to safety and corporate requirements, but also protect against the thermal effects of an arc and flash fire.

 

A patented solution was developed with DuPont™ Nomex® on the outside and DuPont™ Kevlar® on the inside to produce a very high thermal barrier against flash fire and arc. Because of the reaction of Nomex® thickening in a flash fire and Kevlar® providing high tensile strength, when such an event occurs, it creates air pockets in the fabric and therefore provides a lightweight flash fire and arc flash solution.

 

For the Northern Powergrid project two fabrics were worked on: the e+ARC 220RS woven fabric for coveralls and trousers and the A+PANTHER HD 220 RI knitted fabric to make t-shirts and polo shirts. The e+ARC 220RS fabric is developed to specifically protect against the very high level of thermal energy generated by an electric arc. A new concept in the construction of fabrics was used, based in a non homogenous blend to create an intelligent fabric. This means that when the fabric is exposed to high thermal energy, it responds with an asymmetric shrinkage, generating an extra air chamber to protect the person wearing the garment. The blend offers much higher protection than any market solution, especially when taking into account its low weight, which is ideal for those working at Northern Powergrid
Once the design was confirmed and the fabrics approved, a brief was submitted to DuPont manufacturing partner, Dale Techniche. To ensure that only garments of the highest quality were delivered, Dale Techniche matched the e+arc fabric made with Nomex® with state of the art manufacturing processes which were QA controlled by their own staff. Elaina Harvey, Nomex® Account Manager at DuPont, explained, “During the development process the prototypes were also mannequin tested on DuPont™ Thermo-Man® for four seconds to simulate an industrial fire with temperatures up to 1,000 degrees C to ensure they would be fit for purpose. This life-sized instrumented mannequin is one of the most advanced thermal burn injury evaluation devices in the world, giving DuPont the ability to accurately test fabrics and garments under the most extreme conditions. They were also tested on the DuPont™ Arc-Man® test rig to simulate an arc flash, confirming the high protection level of the fabric”.

 

Tailoring and trials

To ensure the sample garments were fit for purpose, Northern Powergrid had a group of around ten staff from each trade groups, including linesmen, jointers and fitters, test different designs trial the garments and make suggestions based on their experiences. Dale Techniche and J & K Ross Ltd engaged with both the group of wearers and the project team in order to assess the feedback received once the garments had been worn for a lengthy period of time. This feedback was then used to fine tune the original designs to ensure both optimum ergonomics and user features were incorporated in the final garment designs before being CE certified.

 

The finished package
Fulfilling the PPE contract included sizing over 1,600 employees, a process that took a team of four people approximately five weeks, across 14 sites in the North East and Yorkshire. Chris Ross, Managing Director of J & K Ross, explained “Each employee was individually sized and the information recorded into a custom database to ensure that when the final kit was received, there would be no doubt that the garments would be fit for purpose.” Prior to the process Northern Powergrid identified the specific product mix each employee required in order that they may be protected from their individual risk exposure (based on the tasks they would be expected to perform). As a result J & K Ross were able to supply them with individual ‘staff packs’ to protect against electric arc flash and other thermal risks. A combination of shirts, trousers, coveralls, waterproof jackets, sallopettes and wind stoppers were provided to each employee in a customised red and black holdall (Northern Powergrid colours) complete with company logo.

Chris continued, “The garment packs are based on a layering system that gives different levels of protection depending on the layers worn for different levels of hazards. Northern Powergrid has developed a simplistic PPE matrix that has also been issued to all operational staff and clearly conveys what level of protection is required for each activity. For subsequent orders every product is ordered through a dedicated online portal so there is a full audit trail of who had what and when.”

The finished package for Northern Powergrid included some 3,500 coveralls, 6,000 t-shirts and polo’s and 3,200 trousers for employees across the Northern Powergrid sites.
Protection in practice
The outcome of an arc flash can be disastrous, especially when working with large volumes of electricity on a daily basis. Through conception to completion, DuPont and its value chain partners, J&K Ross, and Dale Techniche were able to collaborate and combine expertise to provide an appropriate level of protection against arc flash risks for the Northern Powergrid employees. The task of equipping 2,000 employees with new, fit for purpose and individually tailored protective garments was expertly managed, using the knowledge and innovation from each partner, giving a fit for purpose end result.

Since supplying the PPE, the effectiveness in keeping personnel safe was graphically illustrated in April 2013 when two Northern Powergrid engineers working in a substation on an 11,000 volt cable fault experienced a flashover caused by the disruptive failure of a low voltage switchboard. Despite the intensity of the incident, they were able to make an emergency escape from the substation and thankfully were not injured by the flashover. Both were wearing their full arc-flash PPE required for the task that had been carried out in accordance with operational procedures. It was evident that the PPE, effectively a last line of defence in these situations, served its purpose extremely well.