Hot under the collar
Work wear is the first line of defence in the war against worplace injuries, but don’t forget the comfort factor, writes Barbara Schrobsdorff from the Hohenstein Institute.
Protective clothing offers the wearer reliable protection against health risks and environmental effects related to their job which cannot be avoided in their line of work.
Depending on the field of application, textile PPE protects against outside influences such as intense heat and flames, cold and wet, all types of mechanical and physical stresses, from cuts to spray, from molten metal and sparks, through to electricity and electrostatic charges, chemical substances, gases and poor weather.
In many instances, protective clothing requires combined material and functional properties in order to fulfil its intended purpose. Clothing for the rescue services, for example, must guarantee good visibility in traffic in all lighting and weather conditions, offer protection against mechanical and climatic influences (wet, wind, cold) and be constructed in such a way that should it become contaminated with pathogenic agents, the clothing can be treated using a validated disinfection process.
Quite apart from its special functional properties, high quality protective clothing must be comfortable to wear and fit well, otherwise there is a risk that it will not be accepted by the wearer and therefore not used correctly. It must also be kind to the skin and, even after long periods of use and repeated cleaning in commercial laundry conditions, still comply with the requirements and safety regulations for its particular purpose.
COMFORTABLE PROTECTIVE CLOTHING
Protective clothing that is comfortable to wear plays an important part in ensuring that the wearer feels physically at ease doing his job and is motivated to perform well. If physiological comfort is overlooked, it not only makes for a low level of acceptance by the employees, but physical and mental performance also suffer. This is a factor that is all the more important, the greater the risks to which the wearer of protective clothing is exposed in the workplace.
Many different aspects are involved in defining physiological comfort, but it is no longer correct to assume that this is a subjective criterion. Comfort characteristics can be measured objectively. Objective methods of assessment and drawing up guidelines for the design of protective clothing which support bodily functions as well as possible include the thermo-physiological comfort, the skin sensorial comfort and the ergonomic comfort.
It is essential for thermo physiological comfort that body temperature remains within a range that people find comfortable and that puts little strain on the body. The limits are determined by the physiological processes that go on in the body. Since heat exchange in the human body takes place about 90% through the skin, clothing, which covers most of the surface of the skin, plays a crucial role in the way the body’s own temperature-equalising function works. Optimal PPE garments should therefore ensure that the wearer maintains a reasonable body temperature in the widest possible range of ambient temperatures and degrees of exertion.
The materials which are used are an important factor in effective and rapid heat exchange. The comfort characteristics of textile fabrics can be determined by means of a skin model that allows testing for such parameters as thermal insulation, water vapour resistance (breathability), water vapour absorbency, buffering capacities against vaporous and liquid sweat impulses and drying time. In order to be able to make predictions about the comfort characteristics of the finished garment or range of clothing, life-size thermoregulatory models of man, (e.g. in the form of the thermal manikin ‘Charlie’ at the Hohenstein Institute) are used. These simulate heat production in the human body and, in a climate controlled room, also can imitate certain sequences of movements.
The figures that are worked out from particular measurements can then be extrapolated using predictive modelling techniques. This allows making reliable predictions about the range of utility for the garment, e.g. information about maximum and minimum ambient temperatures where it could be used.
The skin sensorial comfort also plays an important role in the acceptance of protective clothing.
Clothing that clings to skin which is wet with sweat is perceived as dragging and restrictive when people move about. Textiles to be worn next to the skin should therefore be napped on the side next to the skin and designed so that they do not stick to the surface of the skin. They should also be made so that they can wick large quantities of sweat away to layers that are not in contact with the skin.
To meet these requirements the most important thing is the construction of the underlying textile from which a garment is made. Sensorial comfort for the skin can also be quantifiably assessed by special measuring procedures. For example, the extent to which a textile ‘clings’ to skin that is wet with sweat is simulated on apparatus to measure adhesiveness, resulting in a wet cling index. Other pieces of apparatus are used to measure the number of contact points between the textile and the skin, and the sorption index.
Ergonomic comfort includes among other things the fit of the clothing. To adequately assess the fitting, garments are tried on by models whose measurements match the size given on the label. The fitting tests for protective clothing, as for everyday wear, are usually based on sizing charts for ladies’ outer clothing and for men’s and boys’ clothes. Experienced clothing specialists assess the garments for length and width, fitness for purpose, ease of movement and functionality, as well as for their appearance. This test should not only be carried out on new garments but also after they have been cleaned, e.g. washed, cleaned and dried. Ideally, the fit of a garment, like the condition of the material or seams should remain unchanged.
“It is essential for thermo physiological comfort that body temperature remains within a range that people find comfortable and that puts little strain on the body.”
IF YOU CAN’T STAND THE HEAT
In many industries such as mining, working in a hot environment is just part of the job. In order to be able to approach a heat source without risking damaging their health, workers have to wear heatproof and non-flammable protective clothing. Hitherto, the main focus when designing this protective clothing for the workplace has been ensuring that it is as effective as possible. How comfortable it is to wear and whether the wearer feels good in it are often of secondary importance.
Hohenstein scientists are currently trying to correct this deficiency by establishing limit values and design principles which could be standardised in order to optimise protective clothing systems for use in hot industrial working environments. The aim of the research project is to include procedures and limit values for measuring physiological properties, taking account of such factors as the ambient temperature, different stress levels, duration of exposure and basic thermal insulation.
In practice it is important to evaluate not only individual garments but also complete outfits, consisting of underwear, outer clothing and outdoor wear such as jackets, in terms of all three comfort factors. Only where there is a combination of the right thermo-physiological, skin sensorial and ergonomic comfort characteristics will the wearer feel good wearing them, resulting in better performance.
TESTING FOR HARMFUL SUBSTANCES
In view of the many specific risks and health hazards to which the wearer of protective clothing is exposed in their workplace, it is important that the clothing should not only have excellent functional properties but should not itself be a source of any danger to health. Textile PPE should not contain any azo dyes, and should have good fastness to perspiration as well as a skin balanced pH-value. Extensive requirements with regard to the human ecological quality of protective clothing, however, are provided by the label ‘Confidence in Textiles – tested for harmful substances according to Oeko-Tex® Standard 100’ that has served as a reliable guide when buying protective clothing for the last 20 years. At the moment, the International Oeko-Tex® Association includes 15 textile testing and research institutes in Europe and Japan, with representative offices in more than 60 countries around the world.
Only these member institutes are authorised to test and certificate textiles for compliance with the specifications of this standardised list of criteria. The Oeko-Tex® Standard 100 is an independent certification system for textiles and garments from all stages of production. Labelled products such as protective clothing are tested for an extensive range of harmful substances based on the latest scientific findings and legal regulations. The label is only awarded if all components of an article meet the defined requirements. The test criteria are universally binding and are adapted to the latest findings every year. They comprise substances which are prohibited or regulated by law, chemicals which are known to be harmful to health and parameters which are included as a precautionary measure to safeguard health. Taken as a whole, they go way beyond national legislation and create an advantage in terms of transparency and comparability against a background of varying environmental standards in the countries of production.
SAFE AS HOUSES TROUSERS: BLADE-REPELLING PANTS
The Hohenstein Institute has developed a new sensor system for cut-protection trousers that could greatly reduce injuries. The principle of the system is very simple, yet effective: if a power saw comes too close to the trousers, the machine is switched off before it even touches the fabric.
Conventional cut protection clothing only provides its wearer with passive protection: the trousers and jacket incorporate cut protection inserts consisting of several layers of special material made of ultra-strong fibres. If the chain of the saw comes into contact with the textile, it becomes caught in the fabric and therefore stops before the wearer is affected. The multi-layered material results in greater thermal insulation, however, which puts additional physiological stress on the wearer, especially at the warmer times of year.
By contrast, with the newly developed electronic protection system, there is no contact at all, and the system kicks in before there is any risk of even the outer textile layer being damaged.
Magnets on the guide bar of the chainsaw and highly sensitive magnetic field sensors (reed switch contacts) incorporated in the textile fabric create a sort of protective electronic field for the wearer. If the saw comes too close, the contacts in the trousers close due to the magnetic field from the chainsaw and a radio signal is sent which stops the saw immediately.
“The principle of the system is very simple, yet effective: if a power saw comes too close to the trousers, the machine is switched off before it even touches the fabric.”
An important benefit of the Oeko-Tex® system is the application-based risk assessment of possible harmful substances in textiles. In general the rule is that the more closely a textile is in contact with human skin, the stricter are the human/ecological requirements that have to be met in testing. Because protective clothing sometimes comes into direct contact with the skin and is also often worn for long periods, it has to satisfy the criteria for Oeko-Tex® Product Class II (textiles in direct contact with the skin).
ESTABLISHING PERFORMANCE LEVELS
The tests carried out on fire-fighting clothing are preceded by preliminary treatment of the materials applied in the form of a care treatment. Possible pre-treatments prior to testing are washing at at least 60° C and then drying the protective clothing in a dryer or commercial reprocessing.
As a rule, clothing soiled with oil, grease or diesel fuel is cleaned in a solvent to produce better results; chemical cleaning should only be undertaken if the manufacturer has not excluded this possibility in the care instructions.
Advice for procurement: Before the protective clothing is pre-treated, ensure that it is suitable for the care procedure planned. During the procurement phase, the type of care treatment to be used should be specified, along with who is to carry out the operation. On initiating the process is should be stipulated who is responsible for checking the PPE, when care treatment is necessary, and how this is to be documented.
PROTECTIVE CLOTHING WITH CERTIFIED UV PROTECTION
An additional benefit of modern protective clothing is reliable protection against harmful UV radiation. People who do their work in the open air or who work in particularly sunny parts of the world are exposed to higher levels of natural UV radiations. In other industries such as the manufacture of UV machines (e.g. sunbeds), employees come into contact with dangerous UV radiation from artificial sources.
In view of the global increase in skin cancer cases, the International Test Association for Applied UV Protection has developed the UV Standard 801. This independent and internationally valid testing and certification system makes it possible to calculate the UV protection factor of textiles objectively. An important advantage of this measuring process is that, unlike other test methods (for example the Australian/New Zealand norm), it also takes account of the condition of the textile product in use, e.g. criteria such as the strain imposed on a fabric by stretching or wetting, or mechanical wear due to wearing and washing.
The figures that are calculated are always based on worst possible scenarios, e.g. assuming maximum UV radiation and the most sensitive skin type. The final protection factor which the customer sees on the label in the garment is based on the lowest measurement taken during performance testing.
Many textile and clothing manufacturers around the world have already taken advantage of the opportunity to have their products certificated by the International Test Association for applied UV protection. The scientifically based benchmark of UV Standard 801 also guarantees the user of protective clothing realistic and reliable predictions about the UV protection provided by the garments they are wearing.
THE HOHENSTEIN INSTITUTE
Founded in 1946, the Hohenstein Institute in Bönnigheim, Germany, has been working for more than 60 years on finding innovative solutions for the whole textile production chain and sees its role as a full-service provider in the fields of application based research, testing and certification. It is also notified as a European Test and Certification Centre for Personal Protection Equipment in accordance with EU Directive 89/686 (Notified Body 0555), and has more than 30 years’ experience in testing and developing protective clothing for clients such as textile manufacturers, manufacturers of ready-made clothing, retailers and importers.
Hohenstein scientists bring together core competencies in the specialist areas of clothing manufacture, clothing physiology, materials testing, textile care, textile finishing and textile hygiene, in a way that is unique in the world.
This article first appeared in OSA Magazine: www.osamagazine.com. Occupational Safety Asia is the dedicated one-stop resource for in-depth, commercially unbiased, high quality articles written by Industry experts from governing and notified bodies.