ASTM F1506 (Standard performance specification for textile materials used in protective clothing worn by electrical workers exposed to instantaneous arcs and related thermal hazards)

ASTM F1506 has developed performance specifications for flame-retardant textile materials used in clothing for electrical workers exposed to instantaneous arcs and other thermal hazards. The relevant requirements of ASTM F1506 protection include vertical combustion method ASTM D6413 (new material after washing) and arc rating.

In addition, the standard requires that the fabric is not easy to be ignited or can contain combustion and extinguish itself after being ignited. The flame retardant performance is tested by the FTM5903.1 vertical burning method (the maximum length of damage after being exposed to the flame for 2 seconds is about 15 cm). The arc rating is assessed by ATPV value or EBT value after passing ASTMF1959 test.

NFPA70E electrical safety requirements standard in working environment: The latest version of the NFPA70E standard published by the National Fire Protection Association in 2004 contains all aspects of safe electrical rules in the working environment of various industries. NFPA70E recommends that in the case of arc generation, arc protection and flame-retardant personal equipment must meet the performance standards of ASTMF1506, ASTMF1891 and ASTMF2178 when used, and the revised version requires companies to conduct arc hazard analysis in advance to determine arcs. Safety boundaries. The standard is set in order to protect employees within the arc safety limits, and protect employees by using protective clothing with the ATPV value of the corresponding hazard risk classification. The unit of ATPV value is cal/cm2, which represents the arc thermal protection value, which is used to reflect the maximum protection performance of arc protection materials, especially arc protection clothing.

NFPA70E sets safe electricity standards for workers working near live equipment, regulates and designs necessary steps to prevent serious injuries caused by arc accidents. According to NFPA70E regulations, every person working within the arc safety limit (the energy released within this range is greater than 1.2cal/cm2) must be competent and wear appropriate flame-retardant arc-proof clothing. NFPA70E divides the hazard risk classification into 0~4 levels to represent different hazard levels.

The minimum risk level is the burn caused by the energy of 4cal/cm2 from the arc explosion, which is the hazard classification of NFPA70E. In order to be adequately protected in the event of an arc explosion, workers must wear thermal protective clothing with an ATPV certified by NFPA not less than Grade 4. Another important rating of arc protective clothing is the HAF rating. HAF stands for thermal attenuation coefficient, which represents the size of the fabric to prevent heat.

ASTMF1891 standard specification for arc-proof and flame-retardant raincoats: This standard applies to flame-retardant and waterproof materials for raincoats. Flame-retardant coatings or laminated fabrics can be used to produce clothing. Its flame retardancy is measured by ASTMD-6413 vertical combustion method, ATPV value also needs to be recorded. Measure 5 times by ASTMF1959 arc thermal performance test method and select the smallest ATPV value to record.

What is an arc

Arc injury generally refers to the arc thermal burn caused by the huge arc heat generated by electricity when the air is ionized when the human body is not in contact with current. Other electrical injuries are often caused by Destructive damage to internal and external human tissues caused when the human body is directly exposed to power current.

Under normal circumstances, what people know more about is accidental electric shock. In fact, the more dangerous thing in the power industry is the hidden arc damage. The arc hazard is often different from other electrical injuries. It is often negligible and difficult to avoid without contact.

Incidental arc event is defined as a non-subjective and unexpected accident. Compared with deflagration, occasional arc accidents are more common. Arc accidents are very rapid. Because safety devices such as circuit breakers are automatically triggered when an accident occurs, the arc duration is often less than 1 second.

The total energy produced by the arc may be more than 3 to 4 times that of a serious deflagration accident. This high energy intensity acts on a small area of ​​the skin in a short period of time and may have a fatal impact on nearby workers. Another significant difference is that deflagration is visible to the naked eye, because smoke is produced during deflagration, half of its heat energy is transferred by convection (flame), and half is transferred by radiation. As for the heat formed by the arc, more than 90% is radiant heat, which means that even if the arc does not produce flames or produces a small amount of flames, it will cause serious damage.

The heat generated by the arc can ignite or melt the protective clothing of workers, which can cause the clothing to crack and cause serious damage to the skin. Burns can be divided into three categories: first-degree burns are painful and the skin is red, but no blisters are formed; second-degree burns are blisters formed on the skin, and the epidermis must be regenerated; third-degree burns will completely destroy the epidermis, and the skin itself cannot be regenerated, forming knots. Scar tissue.

Arc protective clothing must have permanent flame-retardant properties. When exposed to an electric arc, it must not melt or ignite, continue to burn, and must not crack. It can isolate the heat of the arc. Many daily work clothes can be ignited and burned, increasing the burn range of workers. Fabrics that are easily ignited include cotton, viscose, and wool, and fabrics that can be ignited and melted include polyester and nylon. In an arc accident, protective clothing cannot protect against a large amount of thermal energy, which can cause severe burns or even death. Therefore, protective clothing made of heat-resistant and flame-retardant fibers should be used to improve the level of protection against arc hazards.

Note: Level 0 has been deleted in the 2015 edition of the NFPA70E standard

As the weight of work clothes increases, ATPV also increases. In addition, the double-layer light-weight fabric has relatively higher arc protection performance than the single-layer heavy-weight fabric, and is more than twice the protective ability of the single-layer light-weight fabric protective clothing. Its main function is to isolate the air between the two layers of fabric. For example, 220g/m2 comfortable protective clothing has an ATPV value of 8.7 cal/cm2, and the double-layer protective clothing of this fabric has an ATPV value of 33.1 cal/cm2 instead of 17.4 cal/cm2 (2×8.7). The thermal protection performance has increased by 15.7l/cm2.

ATPV is the arc thermal performance value, EBT is the material rupture threshold energy, the unit is cal/cm2, all materials have an ATPV value or EBT value, both values ​​can be recorded but only one is used as the arc rating of the fabric, that is The smallest value. ATPV value: The energy incident on the material has a 50% probability that enough heat can penetrate the specimen to cause a second degree burn. EBT value: The energy incident on the material has a 50% possibility of breaking the sample. When the total area of ​​the holes in the fabric exceeds 1.6cm2 (0.5 square inches), it is broken. They are all tested in the same way as ASTM F1959, and the first reached value is used to record the arc level. If the material's thermal insulation value is greater than the tensile strength, the material will rupture first, otherwise it will burn before it ruptures. If the EBT value is equal to or less than the ATPV value, then the EBT value will be regarded as the arc level value and marked as the arc level (EBT), if the EBT value is greater than the ATPV value, then the ATPV value will be regarded as the arc level value and marked as the arc level (ATPV) ). For example: ATPV: In an 8-calorie test of plain weave fabric, the probability of causing a second degree burn is 50%; EBT: In an 8-calorie test of plain weave fabric, the probability of a one-inch crack on the material is 50%. The two ratings are not good or bad. Basically, EBT fabrics usually have greater insulation than their strength, while ATPV fabrics have more strength than insulation. EBT usually indicates that the clothing is knitted fabrics with better comfort, and essentially does not reduce the protection of the wearer.

BS EN 61482-1-1-2009 Live work. Protective clothing against arc heat hazards. Part 1: Test methods. Method 1: Determination of arc class of flame-resistant materials for clothing (arc thermal protection performance value (ATPV) or EBT50 )

BS EN 61482-1-2-2014 Live work. Protective clothing to prevent arc heat hazards. Test method. Use restricted and directional arc to determine the arc protection level of materials and clothing (in-box test)

Thermal protective clothing: Thermal protective clothing is a variety of protective clothing that protects personnel working under high temperature or ultra-high temperature conditions, so as to prevent the heat source from causing harm to the human body. In a high-temperature environment, wearing thermal protective clothing can reduce the heating rate of the human skin, and provide the wearer with time to react and escape, avoiding or reducing the damage of the heat source to the human body.

There are multiple forms of heat sources that cause harm to the human body, and their properties are different, so the thermal protection performance requirements of thermal protective clothing are also different. The main forms of heat sources are flame (convection heat), contact heat, radiant heat, sparks and molten metal jets, high-temperature gas and hot steam, and high heat generated by electric arcs.

Thermal convection: Convection heat dissipation transfers heat with the movement of fluids such as liquid or gas. The heat release and convection performance of the fabric is closely related to the weight, density, and air permeability of the fabric. Increasing the weight of the fabric can increase the time required to cause second-degree burns to the skin. At the same time, multi-layer fabrics also have better heat and convection protection than single-layer fabrics. B1—B3 in EN11612

Heat conduction: Heat conduction refers to the transfer of heat along an object, from a high-temperature object to a low-temperature object, mainly through continuous collisions between adjacent molecules in the substance. In the application of thermal protective clothing, heat conduction means that the heat takes sparks, molten metal sprays, etc. as the carrier, contacts the clothing and transfers the heat to the human body, thereby causing harm to the human body. D1—D3, E1—E3, F1—F3 in EN11612, small metal splash in EN11611.

Thermal radiation: Thermal radiation refers to the heat radiating outward from an object along a straight line. Its essence is the thermal radiation caused by the temperature of the object, and its magnitude is proportional to the fourth power of the absolute temperature of the heat. Different from heat conduction and heat convection, heat radiation is a non-contact heat transfer method that does not require any substance as a medium, but transmits heat in the form of electromagnetic waves. In the practical application of thermal protective clothing, thermal radiation is one of the main forms of heat transfer that cause damage. Even with flame combustion, its energy includes up to 80% of thermal radiation. In the performance test, the fabric is often exposed to a radiant heat source vertically, and within a specified distance, the heat source radiates heat to the fabric sample, and it is evaluated by measuring the time required to cause the second degree burn of the human skin behind the sample and the heat flux density. The heat radiation resistance of the sample. C1—C4 in EN11612