Assessment of the suitability of protective helmets and eye and face protection measures in potentially explosive atmospheres

Static electricity is common both in natural conditions and in workplaces in industrial environments.

The state of electrification arises mainly as a result of physicochemical changes or processes in which dynamic-kinetic interactions take place. It can also be a direct result of human activity.

The generated electrostatic charge accumulates on materials with low electrical conductivity or on conductive objects insulated with dielectrics with a leakage resistance Ru> 106 Ω. The issue arising from the presence of static electricity and the accumulation of charge mainly concerns:

• chemical industry, including petrochemical (petroleum industry), plastics processing,
• mining industry,
• transport of dangerous substances,
• gasworks and power plants,
• food industry.

This phenomenon may cause a wide variety of disturbances in the work environment. These are mainly:

• fire and explosion hazards,
• technological disruptions in the course of the production process,
• disruptions in the operation of measurement and control equipment,
• unfavorable influence of the emerging electromagnetic fields on the human body.

The presence of static electricity, mainly in places where explosive mixtures may be present, is particularly dangerous from the point of view of the effects on the worker. In European Union law and in Polish law, the Framework Directive 89/391 / EEC and the Labor Code impose on the employer the responsibility for ensuring health and safety protection for employees. This should be done by organizational, technical, collective or personal protective measures.

Legal regulations in the field of protection of the life and health of employees

in potentially explosive atmospheres, it is specified in Directive 99/92 / EC (Directive Atex 137) of 16 December 1999 on the minimum requirements aimed at improving the safety and health protection of workers potentially exposed to the risk of explosive atmospheres. It was introduced into Polish law under the Ordinance of Minister of Economy, Labor and Social Policy of May 29, 2003 (Journal of Laws No. 107, item 1004), as amended, (on the minimum requirements for occupational health and safety related to the possible occurrence of atmospheric atmospheres in the workplace). explosives).

According to the Atex directive, in a zone where there is a risk of explosion, all potential sources of ignition should be eliminated. One of the effective sources of ignition can be static electricity generated as a result of electrifying the human body. Electrification may occur due to the employee's use of inappropriate personal protective equipment. Especially at the moment of their contact and friction with external elements. Clothing, industrial safety helmets, face protection, and footwear are mostly made of plastic, which has a low electrical conductivity and may contribute to the formation of dangerous spark discharges or spray discharges. If the discharge energy is greater than the minimum ignition energy of an explosive atmosphere, it can become a source of ignition. High-energy spark discharges from the surface of the human body are particularly dangerous.

Pursuant to §12 point 3 of the Regulation of the Minister of Economy "... where an explosive atmosphere may appear in amounts threatening safety and health, based on a risk assessment, the working people are provided with appropriate clothing that does not contribute to the emergence of electrostatic discharges. which could ignite an explosive atmosphere ". In the explosion hazard zone, antistatic personal protective equipment should be used. Requirements for these measures were specified in the Regulation of the Minister of Economy of December 21, 2005 (Oz.U. No. 259, item 2173), which transposes Directive 89/686 / EEC on essential requirements for personal protective equipment into Polish law.

Due to the mass production and use of industrial safety helmets as well as eye and face protection made of plastic, the problem of how to assess the risk of explosion from the point of view of the possibility of static electricity arises. Particular attention should be paid to whether:

• the material of which the eye and face protection or the helmet is made may become electrified in the conditions of their use,
• wearing helmets and eye and face protection (putting them on and taking them off) can cause dangerous electrification.

In the conditions of use of the material from which this type of equipment is made, there is a risk of dangerous electrification as a result of:

• friction of external surfaces with fabrics, foils, etc.,
• air movement (especially polluted air),
• solid particle bombardment of the surface,
• internal surfaces rubbing against the user's skin and hair (during putting on and taking off).

Detailed requirements for some personal protective equipment are included in the relevant harmonized standards. For now, there are three standardized test methods (described in the standards harmonized with Directive 89/686 / EEC). Two of them PN-EN 1149-1: 2008 and PN-EN 1149-2: 1999 concern the determination of the surface and / or volume resistance of materials, and the third PN-EN 1149-3: 2007 concerns the determination of the charge decay time and the screening factor for materials clothing.

There are also Polish standards that are not European standards: PN-91 / P-04871, PN-92 / E-05203 and PN-E-05204: 1994, which are not harmonized with Directive 89/686 / EEC.

So far, no Polish or European standards have been developed that would apply to tests of industrial protective helmets as well as eye and face shields that would enable the assessment of their suitability for potentially explosive atmospheres.

Assessment of the suitability of protective helmets and eye and face protection measures in potentially explosive atmospheres

There are several laboratory methods for assessing the suitability of products for use in potentially explosive atmospheres. There are groups of methods that include research:

• the ability to ignite explosive mixtures as a result of electrification of material samples or entire products,
• the value of the charge displaced in an electric discharge,
• electrostatic properties of the materials used in their manufacture.

The third group is the most frequently used, mainly due to the fact that it has the highest repeatability and uniqueness of the obtained test results, compared to the others. They assume that a product can be treated as anti-electrostatic when it is made of a material that does not undergo electrification under the conditions of use or is electrified to an acceptable degree. Within this group, three basic criteria can be distinguished that enable the assessment of electrostatic properties of materials: resistance, voltage and time of electrostatic charge decay. They are characterized by the ability of the material to generate or dissipate an electric charge. In the case where the degree of charge dissipation is greater than its generation, the charge accumulated on the material will be low. The material can then be classified as anti-electrostatic. The assessment based on the resistance criterion consists in measuring the resistance of the material. According to this criterion (PN-92 / E-05203), materials intended for use in potentially explosive atmospheres should have resistance properties not greater than 106 W. The resistance criterion applies only to homogeneous materials and is not appropriate for the assessment many modern composite materials, the elements of which are characterized by different resistance. The voltage criterion states that the surface potential during use of the product in the presence of flammable substances with a minimum ignition energy of W <0.1 mJ should be less than 1 kV. For substances with a minimum ignition energy of 0.1 mJ <W <0.5 J it should be less than 3 kV. When applying the voltage criterion, it must be taken into account that the potential that comes from the surface charge accumulated on the product depends on the properties of the surrounding environment (temperature, humidity), on the spatial distribution of the charge (product shape) and on the test conditions, which do not always correspond to terms of use. The evaluation based on the criterion of the electrostatic charge decay time is based on the measurement of the charge relaxation time, after which the magnitude of the electrostatic charge decreases to 1 / e of its initial value. The application of the criterion in practice is difficult due to the lack of appropriate assessment methods and problems with electrification and charge monitoring.

Selection of protective helmets as well as eye and face protection measures for use in potentially explosive atmospheres

The use of the above-mentioned criteria to assess the electrostatic properties of protective helmets and eye and face protection measures is possible only in a specialized laboratory. Measures are complex products, made largely of rigid plastic elements, from which it is not possible to obtain appropriate samples for testing using universal methods intended for testing fabrics. The user or an employee of OHS services cannot independently assess the equipment in terms of its applicability in potentially explosive atmospheres. If it is necessary to evaluate and conditions for the subsequent operation and maintenance of the equipment, one should follow the information provided by the manufacturers and strictly adhere to the conditions set out in the manuals for the equipment's use. This information must have test results, certificates or equipment conformity declaration.