COATED TOOLS FOR WORKING IN AN EXPLOSIVE ATMOSPHERE
The main danger when working with metal tools in an explosive atmosphere is the production of sparks following rubbing or physical shocks to which the tool is subjected. One known solution for reducing this risk is to apply a coating which protects the metallic part against any physical shocks or
rubbing and which itself cannot generate sparks following electro-static phenomena.
Note: there is no zero risk to the extent that the active part cannot generally be coated, that is why the term reduced sparking tools is used.
The NF E 74-400 standard specifies the characteristics and tests for these tools. The standard recommends that the coating used be of a blue colour.
Field of application :
The NF E 74--400 standard concerns hand tools used in an explosive atmosphere, group II, subdivisions A and B in accordance with NFC 23-514, i.e. the group of gases for surface industries
Example : Class IIA: Propane, Butane, Acetone, Methanol, Natural gas
Class IIB: Ethylene.
Class IIC is excluded: Acetylene, Hydrogen.
The group of Mine gases is excluded.
The standard applies to bending or twisting hand tools (e.g. screwdrivers, spanners, pliers) whereas striking tools (e.g. hammers, shovels, picks) are excluded.
ATEX I and ATEX II tools
The NF E 74--400 standard sets out two types of tools:
- type I: tools for explosive atmospheres
- type II: tools for explosive atmospheres used in an electrical environment (under conditions set out in the standard
IEC EN 60900- 1000V for alternating current and 1500V for direct current).
Note: a type II tool cannot have two working heads with electrical continuity (e.g. two-headed or mixed spanners).
Specific marking identifies type I and II :
- ATEX I symbol for type I tools
- ATEX II symbol for type II tools
Important: the NF E 74-400 standard uses the EXplosive ATmosphere abbreviation (ATEX) for marking the tools which should not be confused with the classification of the ATEX 0,1 or 2 zones of the product marking E.g. the ATEX 94/9/EC directive.
For use -40°C, C marking indicates that the tool has been designed for this purpose.
Checks & Tests :
The blue coated tools must satisfy the tests of standard NF E 74-400:
- Physical shock tests
- Insulation resistance test to check that the coating does not create sparks (electro-static charges)
- Dielectric test (solely for ATEX II type)
- Adherence of the coating
- Flame non-propagation test
The insulated tools are designed to preserve their characteristics despite the difficult conditions of use inherent with on site work. However, they should be properly stored and kept clean.
The coating can be cleaned with soap and water (rinsing + drying ) whereas the metal parts must be regularly greased.