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One in the Eye for Safety and Testing

Published: 10th May 2012

WE’VE COME A LONG WAY

Those of you who may have the misfortune to know me personally will know that along with my interest in 50s and 60s music, I am a modified classic and customised car enthusiast, or ‘Hot Rodder’ – which, when placed out of context, makes me sound like an expert in the swift expedition of unexplained blockages in the sewage department.

In actual fact, it means that I like to take an old classic car and modify it, usually by putting in a big engine and making other drivetrain modifications in order to go fast and recapture the excitement of my youth.

It was about nine or ten years ago - before my current job - while modifying a 1961 Humber Hawk to take a 5L V8 Ford Torino engine that I fell foul of a power tool. I discovered that due to the new lower stance of my ride that the whole propshaft tunnel needed to be modified to prevent fouling, so I took out the nine inch cutter and prepared to make the first incision.

I stopped short, reminding myself that I probably ought to have some protective gloves and eyewear, so I donned the available articles and set about my cutting of the car floor. I made great progress but had failed to check the necessary precautions needed for the job.

As I made a particularly long cut, a white hot needle like shard of metal shot up and over my slip on safety glasses (I was bending) and embedded itself in my left eye. A trip to the hospital, an operation and some considerable pain and discomfort followed.

If I had taken the necessary precautions and worn the correct safety gear, then that could have been avoided. When you look at the available array of differing items of personal protective equipment (PPE) available it can be somewhat confusing,?and sometimes unclear as to what to buy, particularly where a safety standard is involved.

What do these standards mean? Who comes up with them? Are they really necessary? For example, it’s very difficult to explain to a company who have worn one particular type of Flame Resistant (FR) apparel for as long as they can remember, that it's actually not really fit for the job. It may have been what was available 20 years ago, but times and fabric developments change – and as I found out, you can very easily be under protected by not knowing the facts.

Ironically, but now with much more education, I’m often asked as a FR apparel professional to provide details of relevant safety standards and the different tests used to attain compliance – and that got me thinking. Where did it all start? I mean – how did we arrive at the point we are at now, and what’s behind the regulations? In my position I am very privileged to know some renowned industry experts, so instead of trying to get my head around it all and then make it interesting, what better place to start than with one of those aforementioned people to assist in making me look like I know the answers? I asked a colleague from one of the world’s largest apparel companies to lend me her expertise. This colleague is widely respected in the FR apparel industry and sits on several safety panels, assisting with the development of safety standards. Although the information that follows is predominantly US based, European testing methods aren’t too different, and many of the standards emerging in the Middle East are taking their lead from those already tried and tested – and established – in both the US and in Europe.

Testing flame resistant fabrics and garments

As industrial safety standards have improved, employers and employees have demanded better performing and more protective flame resistant clothing. Performance standards have challenged all levels of the supply chain to produce higher quality products that meet the rigorous demands of the day – not only for protection against thermal hazards, but also for comfort, durability and overall value. All flame resistant fabrics can be grouped into two broad categories which describe their source of the FR capability: fabrics are either inherently FR or FR treated. Inherently FR fabrics are made of fibres or a blend of fibres whose polymeric structures prevent them from sustaining combustion. No additional finish or treatment is required on the fabric to make it flame resistant. FR treated fabrics, of course, are non-FR goods – usually cotton or cotton/nylon blends – which are treated with a durable chemical finish which delivers the desired flame resistant properties. Although a host of test methods exist for evaluating flame resistant fabrics, there are two fundamental tests run on every fabric used in FR protective clothing. Typical requirements of most performance standards are that a fabric passes a vertical flammability test (ASTM D6413, formerly FTS 5903) with less than two seconds of after flame, and a maximum char length of four to six inches. In addition, the fabric is not allowed to ignite, melt, drip or shrink more than ten percent when subjected to a 500° F oven for five minutes. These requirements would be considered the absolute minimum performance for clothing intended to protect from a thermal hazard. Flame resistant fabrics and garments first appeared on the market in the 1970s, but the first national performance standard written specifically for flame resistant workwear was NFPA 1975, Standard on Station/Work Uniforms for Emergency Services. Its inaugural version was published in 1985. Although it was written with firefighters in mind, it became the model for other standards that were developed by and for industries needing to protect their employees from specific thermal hazards. Industry groups felt a need to more fully define protection for their specific hazard, particularly flash fire and electric arc. These new standards have their foundation in baseline FR performance requirements, but are defined for specific thermal threats by the addition of tests that attempt to simulate the potential field exposure in a laboratory setting. What were once considered exotic tests used primarily for research and development purposes have become mainstream tests required by the most frequently referenced performance standards in industry.

Flash fire protection

NFPA 2112, Standard on Flame Resistant Garments for Protection of Industrial Personnel Against Flash Fire, has become the recognised performance standard for garments worn by workers potentially exposed to a flash fire event. It is routinely cited by safety managers in the oil, gas and chemical industries. In addition to vertical flammability and heat resistance tests, other performance characteristics such as a fabric’s ability to provide insulation, and its propensity to prevent body burn, have been added to the document to make it even more applicable to workers in these environments. The use of the instrumented manikin has become part of a standard battery of tests needed to fully evaluate and understand the protective qualities of a flame resistant fabric. There are four instrumented manikins in North America that are used to predict the percentage body burn that can be expected when the manikin is clothed in a standard coverall made of the candidate fabric. The manikin is covered with more than 100 sensors, each of which monitors a section of the manikin’s skin. Following the standard three second exposure at a heat flux of 2.0 cal/cm2 – as required by relevant ASTM F1930 test method – computer generated output predicts the degree and extent of burn injury that the manikin has sustained. NFPA 2112 requires that the predicted body burn injury be no more than 50 percent for a fabric to pass this phase of compliance testing.

Electric arc protection

Likewise, workers with potential exposure to an electric arc while on the job were in need of a performance standard that addressed their safety concerns with regard to possible garment ignition. So, within a few years, ASTM F1506, Standard Performance Specification for Flame Resistant and Arc Rated Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards, was published. It defined the characteristics of fabric and garments intended to protect electricians, electric utility workers and the like from clothing ignition caused by exposure to an electric arc. Arc testing on protective fabrics and other pieces of PPE requires a specially equipped and professionally staffed lab that has access to plenty of power. It is a specialised field of testing that only a few labs in the world can do properly. Testing for the flame resistant clothing market has primarily been conducted on single layers of fabric, but changes in relevant standards have induced the need to evaluate layers of fabric that represent insulated garments or multiple articles of apparel being worn together. The result of exposing a fabric or a composite of fabrics to electric arc is an ATPV (arc thermal protective value, expressed in cal/cm2) which is the maximum incident energy at which a wearer stands a 50 percent chance of sustaining a second degree burn while wearing a garment made of the candidate fabric(s).

What about being just ‘FR’?

Although more sophisticated methods of testing have been developed over the years, the vertical flammability and heat resistance tests continue to form the basis for most FR clothing standards. They are applicable to any workplace environment that poses a threat of thermal exposure to the end user. In 2003, ASTM F2302, Standard Performance Specification for Labeling Protective Clothing as Heat and Flame Resistant, was published, and is the document that even today still defines these minimum requirements for clothing that can be called ‘FR’, or flame resistant. When management mandates that employees simply wear FR clothing at work, this is the performance standard that is most often cited.

Testing for FR durability

Early versions of FR treated fabrics were not particularly durable to laundering. Garments made of these fabrics were used in settings where laundering was infrequent, and it was anticipated that the garment would be worn out and retired prior to the loss or reduced effectiveness of the FR treatment.

These garments were advertised to last through about 25 cycles of laundering, and it was recommended that the owner/wearer of the garment would carefully track the number of cycles of laundering that the garment had sustained. Although the FR chemistry has remained essentially unchanged, today’s FR treated fabrics have improved durability to laundering, and many clothing brands will guarantee that the FR properties will exist for the life of the garment if the recommended laundering procedures are followed. There is still a cautionary note made to end users that repeated exposures to copious amounts of chlorine bleach could alter or disturb the FR chemistry on the fabric, and possibly reduce the FR capabilities of the garment. In addition, despite vast improvements in the durability of the FR performance, virtually all performance standards for flame resistant fabrics and clothing require that tests be conducted both before and after multiple cycles of laundering.

Beyond performance standards

It is traditional that performance standards set requirements related to properties that affect the protective qualities of a fabric or garment. Like all consumers, wearers and purchasers of FR garments are equally interested in factors that create value – product features that enhance comfort and durability. Over the last 20 years, significant strides have been made on the protective capabilities, so researchers have begun to focus more of their attention on making FR clothing more comfortable to wear.

The demand for comfort

Beyond issues of protection, end users are equally interested in advancing the comfort of FR clothing. Performance standards typically do not address comfort properties or requirements because they are not related to the safety of the wearer. Nevertheless, consumers have come to expect and will continue to demand improvements in fabrics and garments that make clothing more comfortable to wear.

Defining what makes a fabric or garment comfortable is an indefinite science. The very subjective ratings of comfort are based heavily on individual preferences and personal opinions. Textile scientists have devoted entire careers to defining, measuring and evaluating the comfort of clothing. There are some factors that everyone agrees contribute to a feeling of comfort in a fabric and garment: weight, softness, flexibility, for example. Beyond these, some advanced testing that is commonly conducted on fabrics includes:

• Wicking – A fabric’s ability to transport moisture. This is a characteristic that is regarded as essential to comfort, especially in warm climates or when the wearer is working. Fabrics that do not move moisture from the skin surface usually result in wearers complaining of garments making them feel hot and clammy inside the clothing

• Total heat loss – This is the amount of conductive and evaporative heat loss through a fabric or layers of fabric. This measurement is significant to wearers who may suffer the effects of heat stress due to extreme environmental conditions and/or moderate to heavy physical activity required by their jobs. A performance standard setting a minimum total heat loss requirement prevents an employee from donning apparel which could exacerbate the onset of heat stress

• Clo – This is the amount of insulation required to maintain normal human skin temperature. Related to total heat loss, clo serves as a means of characterising the insulative capabilities of cold weather gear. Although not yet common in the FR clothing industry, it has become a popular system of rating insulated outerwear in the consumer market The need to define and measure the protective capabilities of flame resistant clothing is exceeded only by the desire of end users to know more about how their clothing performs. The increased demand for data used by purchasing agents to compare products and by marketers to showcase their offerings will continue to drive the development of new and more comprehensive test methods. Researchers and scientists who are devoted to the flame resistant clothing industry are pleased to work overtime knowing that their efforts serve to keep workers safe from clothing ignition, while facing the dangers of their every day working life.

Published: 10th May 2012 in Health and Safety Middle East

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Paul Toplis