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Protective Clothing [Sept 2010]

Published: 01st Sep 2010 in OSA Magazine

Workers are exposed to heat and fire hazards in many industrial workplaces, and are thus at risk of burn injuries.

Occupational burns are classified according to type of exposure 1:

• Thermal burns
Heat from explosions, flame, radiant heat, heat from hot contact

• Electrical injuries
Electrical explosions, flashes, direct contact with electrical current

• Chemical burns
Reaction of biological tissue with chemical substances and materials
Burn injuries are divided into three groups according to severity 2:

• First degree burns are the most common type of burn injury. They involve only the top layer of skin and are characterised by pain, redness,
and swelling. Sunburn is a typical first degree burn

• Second degree burns involve the
first and second layer of skin. They
are characterised by blistering of the skin, redness, and swelling, and are
very painful

• Third degree burns are the most severe, and often result in extensive scarring. They can require a long recovery time and may result in severe limitations

The Finnish Accident Register contains records of serious accidents which have been investigated by occupational safety and health authorities and have led to either death or severe injury (permanently disabling injury or absence of more than one year from work). From this source, I found the following victims with burn injuries either leading to death or connected to protective clothing in the accident event sequence, by occupations, between 1994 and 2007 3:

Clothing of sheet-iron worker ignited during flame cutting - flame retardant protective clothing or other suitable personal protective equipment (PPE) was not used.

Clothing of pipe fitter ignited from burning oxygen/acetylene - flame retardant protective clothing or other suitable PPE was not used.
Hot alkaline chemical splashed over a worker in pulp mill - instructions for use of PPE were missing.

Sparks from grinding machine ignited clothing of pipe fitter - suitable protective clothing was not used.

Hot water and wood chips splashed over worker in pulp mill.

Electrician in nuclear power plant killed by an electric arc - flame retardant protective clothing was not used.

Protection needs in the metal industry

Workers in the metal industry often suffer burn injuries as they are exposed to sparks, hot surfaces, molten metal splashes, radiant heat, flames, and hot materials. Occupations are, for example: blow pipe cutters, scrap handlers, smelters, ladle operators, work tutors, relief workers, masons, heat treatment workers, moulders, core makers, pattern makers, crane operators, truck drivers, cold smiths, welders, mechanics, and electricians.

The tasks of some workers’ groups are outdoors. In these cases, the exposure depends on the weather conditions. Therefore, in addition to heat and fire, protection from cold or foul weather may be needed. Draft is often a problem during the wintertime. Workers may often also be exposed to chemicals such as quartz dust, paint dusts, steel fumes, welding fumes, carbon monoxide, curing water oil, or physical hazards such as noise. In these cases, other types of PPE, such as head protection, respiratory protection, hearing protectors or protective gloves are needed. Welders are a typical example of an occupation in which several items of PPE are needed simultaneously. Workers working in dark areas or areas with moving engines need to be visible with the help of bright colours and reflective materials. They also often work on their knees and need protection of this area.

Requirements for use of heat protective clothing

Council Directive 89/656/EEC on the use of PPE 5 says that “PPE shall be used when risks cannot be avoided or sufficiently limited by technical means or collective protection or by measures, methods or procedures of work organsisation. Personal protective equipment must comply with the relevant requirements of the community on design and manufacture with respect to safety and health. Heat protective clothing, as all PPE equipment must:

  • Protect against risks at the workplace, without causing any increased risk
  • Meet ergonomic requirements and take into account the worker’s state of health
  • Fit the wearer correctly after any necessary adjustment

If, in addition to protective clothing, the workers must wear other items of PPE for complete protection, it is important to check that all the equipment used is compatible.

To assist employers (or the person who advises the employer) in making the necessary decisions regarding the selection, use, care and maintenance of protective clothing for employees exposed to risks related to heat and flame, CEN TC 162 has prepared a guidance document CEN TR 14560: guidelines for the selection, use, care and maintenance of protective clothing against heat and flame. The purpose of this document is to highlight the main areas that an employer needs to consider. Most paragraphs of the document contain bullet-lists, serving as check lists of matters to be taken into account.

Requirements of the products

The User Directive provides help for selecting and using PPE which complies with the relevant safety and health requirements. These are the basic values in the product directive on PPE 89/686/EEC 6. It generally harmonises the requirements for different types of PPE, ensuring a high level of protection for citizens, and free circulation of products throughout Europe.

As regards to heat and fire protection, the Directive states that “complete PPE ready for use” must protect the user so that “the quantity of heat transmitted by PPE to the user must be sufficiently low to prevent the heat accumulated during wear in the part of the body at risk from attaining, under any circumstances, the pain or health impairment threshold. PPE must if necessary prevent liquid of steam penetration and must not cause burn resulting from contact between its protective integument and the user.”

The European Committee for Standardisation (CEN) and the European Committee for Electrotechnical Standardisation (Cenelec) are competent bodies which have been authorised to adopt harmonised standards in accordance with the general guidelines agreed on between the Commission and the European standards organisations.

For the manufacturer, the application of European harmonised standards is voluntary, as is the case with all ‘New Approach’ directives. However, as the application of a harmonised standard requires conformity with the basic health and safety requirements Directive that
is covered by the standard, most manufacturers follow the harmonised standard when designing heat protective clothing.

Three basic harmonised standards define the requirements for protective clothing against industrial heat hazards.

1. EN ISO 14116 Protective clothing - Protection against heat and flame - Limited flame spread materials, material assemblies, and clothing.

This standard is intended to protect workers against occasional and brief contact with small igniting flames, in circumstances where there is no significant heat hazard and without the presence of any other type of heat.

It is used as a basic standard for the other standards defining protection against heat hazards 7.

2. EN ISO 11612 Protective clothing - Clothing to protect against heat
and flame

This standard provides minimum performance requirements for clothing to protect against heat and flame, which may have a wide range of end users. It provides the minimum requirements at three performance levels:

  • Level 1 - to indicate exposure to low risk
  • Level 2 - to indicate exposure to medium risk
  • Level 3 - to indicate exposure to high risk

For protection against exposures to radiant heat, there is a fourth performance level for high performance materials such as aluminised and similar materials 8.

3. EN ISO 11611 Protective clothing for use in welding and allied processes

This standard specifies minimum basic safety requirements and test methods for protective clothing including hoods, aprons, sleeves and gaiters that are designed to protect the wearer’s body, head and feet, and that are to be worn during welding and allied processes with comparable risks. This standard specifies two levels of performance:

  • Class 1 - protection against less hazardous welding techniques
  • Class 2 - protection against more hazardous welding techniques

In addition to heat and fire protection, these standards also define the minimum requirements for strength, innocuousness and dimensional change. Table 1 summarises the requirements of these three standards for heat and fire protection 9.

Heat and fire test methods

The flame spread test is the basic test for all kinds of heat protective clothing. The EN standards for heat protection refer to ISO 15025 procedure A, and EN ISO 11612 also to procedure B. According to this method, a flame of 25mm in height is exposed to the surface of the sample at a distance of 17mm, for ten seconds. Afterflame and afterglow time are measured and must be ≤ 2 s. No flaming to top or side edge, molten debris, or hole formation is accepted, except for a layer used for specific protection such as liquid protection. The flame is applied to both sides of the component assembly, including wristlets and seams as well as other additional material.

Radiant heat test method

EN ISO 6942 specifies two complementary methods (method A and method B) for determining the behaviour of materials for heat protective clothing when exposed to radiant heat. Method A serves for visual assessment of any changes in the material after a heat radiation of 10 kW/m² for three minutes.

Any changes (e.g. discolouration, deposits, smouldering, charring, rupture, melting, shrinkage, sublimation) are noted separately for each layer of the sample. Method A is also used as a pre-treatment of the material samples for subsequent tensile strength testing. The minimum value for tensile strength after this pre-treatment is 450 N. Method A is required only for fire fighters’ protective clothing. Method B determines the protective performance in the Radiative Heat Transfer Index (RHTI) of the materials. The radiation is produced by six silicon carbide heating rods, and a copper disc/copper-constant thermocouple is used to measure the temperature behind the test samples.

A heat flux density of 20 kW/m² is used to measure performance against radiant heat.

Convective heat test method

Heat transmission on exposure to flame in the EN ISO 11612 standard is determined using ISO 9151:1995. In this method, a horizontally-orientated test specimen is partially restrained from moving and subjected to an incident heat flux of 80 kW/m² from the flame of a gas burner placed beneath it. The heat passing through the specimen is measured by means of a small copper calorimeter both on top of and in contact with the specimen.

In EN ISO 6942, as well as in ISO 9151, the time in seconds that it takes for the temperature in the calorimeter to rise to 24+0.2 °C is recorded. The mean result for three test specimens is calculated as the Heat Transfer Index (HTI).

Contact heat test method

EN ISO 11612 also classifies protection against contact heat. It uses the EN ISO 12127-1 test method, in which a heating cylinder is heated up to the contact temperature and the specimen is placed on the calorimeter. The heating cylinder is lowered onto the specimen supported by the calorimeter or, alternatively, the calorimeter with the specimen is lifted up to the heating cylinder. In each case the operation is carried out at a constant speed. By monitoring the temperature of the calorimeter, the threshold time classification (three levels) is given in
EN ISO 11612, and it requires a contact temperature of 250 °C.

Thermal resistance of materials

ISO 17493 tests the heat resistance and thermal shrinkage for each material used in a garment, including the wristlet. Material specimens (375 x 375 mm) are suspended in a hot air circulating oven for five minutes at the specified test temperature of either 185+5 °C or 260+5 °C. Any ignition, melting, dripping, separation or shrinkage of the specimen is recorded. The exposure temperature varies depending on the standard. The main requirement is that materials to be used next to the skin must be exposed to a temperature of 260 °C. No melting, dripping, separation, or ignition is accepted.

Electric arc test method

The risk of electric arcs is not covered very well in the above standards. Annex F of EN ISO 11612 handles protection against the thermal effects of an electric arc event. The annex refers to IEC test methods IEC 61482-1 and IEC 61482-1-2. We currently also have the EN standard EN 61482-1-2 ‘Live working. Protective clothing against the thermal hazards of an electric arc’. Part 1: Test methods. Part 2: Determination of arc protection class of material and clothing by using a constrained and directed arc (box text), which is based on the corresponding IEC-standard. If the protective clothing is intended for the use of electricians in the EU, it is EC-type examined according to EN ISO 11612, and EN 61482-1-2 (or IEC 61482-1-2) is mentioned as an additional required test to be carried out. The electric arc is produced by Cu/Al electrodes with a cap of 30mm, and placed in a test box made of plaster. It is designed to direct the energy of an electric arc to the samples, thus intensifying its effect, so that a lower test current can be used. The electrodes are placed vertically; the upper electrode is aluminium and the lower copper. The supply voltage is 400 V, and the duration of the electric arc is 0.50 s. The prospective test current is 4 kA in class 1 and 7 kA in class 2.

The test conditions are intended to be comparable to accident situations in low-voltage installations and networks 10.

Materials of heat protective clothing

The typical fabric used in CE marked products weighs 250-400 g/m² and is either satin or twill. The fibre content may be 100% cotton durable finished by e.g. Proban or Pyrovatex. The flame retardant or cotton can be mixed with polyester e.g. Trevira CS with 75-50% cotton. Cotton can also be mixed with polyamide, normally 12-15% polyamide. Polyaramide fibres such as Nomex, Kevlar, Twaron are now increasingly used for heat protective clothing in pure or blended fabrics. Flame retardant viscose and wool are used in blends because of their poor strength properties. Often the fabrics have been mixed by 1-2% antistatic fibres to make the products electrostatic dissipative and to meet the requirements of EN 1149-5. These types of heat protective clothing are used as part of a total earthed system to avoid incendiary discharges.

To protect exposures to a light spray, liquid aerosols, or low volume chemical splashes, the fabrics are finished by fluorocarbons to meet EN 13034 requirements. A typical example of multipurpose fabrics is a one which, in addition to heat protection requirements according to EN 11612 and/or 11612, meets those of EN 471 for high visibility, EN 1149-5 for electrostatic dissipative, and EN 13034 for limited protection against liquid chemicals.

Conclusions

The minimum performance requirements for clothing to protect against heat and flame are specified for a wide range of end uses. However, performance requirements are still missing in some areas. In pulp mills, workers are exposed to splashes of hot liquid alkaline chemicals or hot water, sometimes leading to serious accidents. Standardised requirements and test methods are currently unavailable, and information on suitable materials is also lacking.

References

1 http://fi.wikipedia.org/wiki/Palovamma (burn injury)
2 Fordyce TA, Kelsh M, Lu ET, Sahl JD ja Yager JW: Thermal burn and electrical injuries among electric utility workers, 1995-2004. Burns 33 (2007) 209-220
3 Mäkinen Helena: palovammat ja henkilönsuojainten käyttö. Työ ja ihminen 21(2007) 4, 453-464 (In Finnish with English summary)
4 Helena Mäkinen: Risk assessment for the selection and use of protective clothing - a practical example, Finnish Institute of Occupational Health, 3rd Seminar on PPE in Europe, 1996, page 57 - 62
5. Council directive of 30 November 1989 on the minimum health and safety requirements for the use by workers of personal protective equipment at the workplace (89/656/EEC), Official Journal of European Communities 30.12.89
6 Council directive of 21 December 1989 on the approximation of the laws of the Member States relating to personal protective equipment (89/686/EEC), Official Journal of European Communities 30.12.89
7 EN ISO 14116:2008. Protective Clothing. Protection against heat and flame. Limited flame spread materials, material assemblies and clothing
8 EN ISO 11611:2007. Protective clothing for use in welding and allied processes
9 EN ISO 11612:2008. Protective clothing. Clothing to protect against heat
and flame.
10 IEC 61482-2: Part 2: Flame resistant materials for protective clothing and 61482-1-2: Thermal hazards of an electric arc - Part 1: Test methods - Method 2: Constrained and directed arc (box test). International Electrotechnical Commission (IEC) 2007

Author:

Helena Mäkinen, PhD (eng), team leader
Finnish Institute of Occupational Health
Protection and Product Safety
Topeliuksenkatu 41 aA, FI-00250 Helsinki

T: +358304742764

F: +358304742115

E: helena.makinen@ttl.fi

W: http://www.ttl.fi

Dr Helena Mäkinen is team leader for team Protection and Product Safe at the Finnish Institute of Occupational Health. The team offers testing, certification (Notified Body
no. 0403), training and quality management system services related to Personal Protective Equipment (PPE). She is also working in many EN and ISO standardisation groups especially in areas of heat protection and has led many research projects in the area of heat protection.

Published: 01st Sep 2010 in OSA Magazine

Author


Helena Makinen


Helena Mäkinen,Team Leader
Protection and Product Safety

Finnish Institute of Occupational Health (FIOH) Centre of Expertise for Work Environment Development Protection and Product Safety Topeliuksenkatu 41 aA, 00250 Helsinki, Finland


Helena Makinen

Website:
http://

Email:
helena.makinen@ttl.fi

Phone:
+358 304741

helena.makinen@ttl.fi
http://
+358 304741

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