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The Useful Life of PPE

Published: 01st Aug 2009

TESTING PROTECTIVE WORKWEAR FOR PERFORMANCE

It is vitally important that any item of personal protective equipment (PPE) performs adequately throughout its lifetime. User instructions supplied with the item usually include advice to visually inspect and check for physical damage, but in some cases it is not possible to assess if a product still provides the same level of protection as when new.

Examples include high visibility clothing that may have faded or been contaminated, clothing intended for heat and flame applications where continual washing may have reduced the fire-resistant properties of the fabric and fall protection equipment where webbing or rope may have suffered abrasion damage.

PPE Performance

EC Directive 89/686 requires all PPE to be supplied with instructions for use which amongst other things need to address the 'obsolescence deadline', which is defined as the date after supply or being put into use on which the PPE becomes incapable of fulfilling its intended use.

This means that the manufacturer must provide all information necessary so that the user can determine a reasonable period of obsolescence. In terms of inspection prior to using the PPE, the manufacturer must also provide guidance on how to recognise unacceptable damage or signs of ageing such as cracks in materials or abrasion to webbing. Most test procedures and standards for PPE recognise that the protective features may deteriorate with use and include at least one test or requirement in an attempt to assess this degradation. However, the ageing process is a complex issue that depends on many environmental factors, most of which are hard to replicate with a simple and quick laboratory procedure.

Typically, heat and flame clothing standards may include a requirement to wash an item of PPE several times before reassessing its burning behaviour characteristics to ensure an acceptable level of protection will remain after cleaning in use. High visibility garment standards include rechecks on colour after subjecting fabrics to UV light from a high-intensity xenon lamp to assess potential fading under periods of simulated exposure to sunlight.

Whilst these simple tests go some way to demonstrating material behaviour, they do not generally replicate everything a garment will be subjected to during its life, and do not simulate the more complex interactions. For instance, repeat washing of garments is not the same as real-life use where between washing cycles the garment will be worn which will subject the fabric and seams to conditions that may involve contamination, flexing, UV radiation and mild abrasion. The service life will also depend on storage conditions between use and the effectiveness of any maintenance.

Other standards, such as those in the fall protection arena, rely on safety factors built into the performance levels, which it can be argued allow for a certain level of degradation or reduction in strength before the product will no longer work effectively. But again it is difficult to know what safety factor is acceptable and what level of degradation can occur before the damage is sufficiently visible. With all equipment, the importance of a pre-use inspection by the user cannot be overstressed.

Where items of PPE are relatively low cost and disposable after a short time, concerns about maximising the use of the PPE are less important (as long as the PPE always meets the performance requirements). However, some PPE such as firefighters' clothing and equipment is expensive to replace and therefore the lifetime of the product is a significant issue to the employers responsible for its purchase and maintenance.

In these situations, manufacturers need to establish how their products perform under a variety of conditions typically encountered in use to estimate obsolescence. The closer these can be made to simulate user conditions, the more accurately the product life can be determined and the more confident a manufacturer can feel regarding claims made.

SID SATRA Instrumented Dummy

Understanding how materials and products perform when exposed to sources of heat and flame is fundamental to developing apparel and associated equipment intended to protect wearers from these hazards.

Traditional small scale material testing, detailed in conventional European and international flammability standards, does not simulate what happens in real life scenarios such as that experienced by fire rescue workers or others. Here the clothing may be exposed to large-scale fires, and must provide adequate protection under those circumstances. In these situations the design and construction of the garment, and the way it is worn and sits on the body of the wearer can both have a crucial affect on heat and flame protective qualities, which can only be accurately simulated by subjecting the clothing to some form of whole garment test.

Human form manikin testing provides additional information which demonstrates more realistically the behaviour of apparel and provides manufacturers and users with a better understanding of the characteristics of high performance materials and clothing under these conditions. The results of fire tests conducted in this way are an important consideration for manufacturers and users of garments intended to provide protection during complete flame engulfment situations.

The use of manikins in European safety standards directly related to PPE testing and CE marking is still in its infancy, therefore, currently most heat and flame manikin work is undertaken as research and development, on materials and apparel prior to production.

However, this is anticipated to change in the future as standards makers continue to revise and update PPE standards. The revised EN 469 (Protective clothing for fire fighters) for instance details the use of a manikin as an optional garment test.

SATRA has three heat and flame manikins (all called 'SID' - SATRA Instrumented Dummy). The neck, shoulders, elbows, hips, knees and ankles of the SATRA manikins are articulated. Not only does this aid donning the clothing, but it is also possible to manipulate these parts to test apparel in a variety of positions. The 1800mm tall body is covered in thermal sensors, which are monitored using a sophisticated logging system, capable of recording data 100,000 times per second. The manikin facility has been designed to assess all types of clothing including gloves, headwear and footwear.

The flame source is a series of four vertical propane burner stations that can be placed at any position around the manikin to provide a uniform heat flux of up to 84kW/sq m. Each burner station incorporates five equal-spaced burners, each with an overall nozzle diameter of 50mm. Although the burners are applied for only a few seconds at a time (3 to 8 seconds typically) a considerable intensity of flames and heat can be produced.

During these tests it is possible that physical changes will occur to the garment which cannot be adequately predicted by the small scale swatch tests. In these incidents a wearer may sustain significant burns to a large area of his or her body, which might ultimately prove fatal. The burns however could occur in a number of ways. Firstly the textiles and composites may simply allow the heat flux to pass straight through the garment. Secondly, the garment might catch fire and become a secondary source of radiant heat only a few millimetres from the wearers skin. Thirdly, the garment might shrink thus bringing the heated materials into very close contact with the skin. It is, however, likely that all three mechanisms may play some role in injury.

The purpose of manikin testing is to measure the effectiveness of protective clothing in reducing or eliminating skin burn injuries to the wearer. Human skin consists of a number of layers. The outermost layer, the epidermis, is normally approximately 50-80?m thick. The next layer is the dermis which is around 1.5 to 2 mm thick. The layer below that is the sub-cutaneous layer. First degree burns are defined as reversible damage to the epidermis layer and a second degree burn is defined as damage to the dermis/epidermis which may be irreversible. A third degree burn destroys the epidermis and dermis and may damage sub-cutaneous tissue.

The software which controls SID has been written to calculate the resultant heat flux/time exposure from the temperature/time profiles for each sensor, and predict whether the level of burn for that sensor is none, first, second or third.

Using data from all sensor positions it is possible to build a picture of the total area of burns over the whole body. Protection is dependent not only on the basic protective qualities of the textile or composite but on factors such as: i) how the garment sits on the wearer, ii) the quality of the fit, iii) the presence of air gaps between the different layers or between the clothing and the skin of the wearer. The presence of undergarments can also have a significant effect on protection. The test can be used to compare different materials or different weights of the same material, different garments, or similar garments with different undergarments. Given that fit can be an important factor, the test can be used to compare the effects of a loosely fitting garment compared to a tightly fitting garment.

Manikin testing was introduced as a way of determining the effects of flame engulfment on a complete item of clothing and the wearer. In some areas of testing human subjects can be used for whole garment evaluation but this is obviously out of the question when testing the protection of whole garments against flame engulfment. The use of SID, coupled with other tests such as mechanical and physical testing and laundering processes, enables SATRA to provide manufacturers and end users access to a state of the art facility to assess their products under the most arduous of conditions.

Author

SATRA is the world's leading research and technology centre of its kind and employs more than 180 scientific, technical and support staff in the UK and China. The brand is recognised and respected in over 70 countries.

SATRA's objective is to help its customers increase their competitiveness. It provides support and expertise throughout the whole supply chain, from product research and development, material and component evaluation, quality assurance, manufacturing efficiency and cost saving, to testing and certification. SATRA also builds and sells its own branded test equipment.

www.satra.co.uk

Published: 01st Aug 2009 in Health and Safety Middle East

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Peter Doughty