Flameproof Applications

Source Reprinted from RK Carbon Fibres technical literature. 

Property Typicai value for Panox oxidized PAN fiber (opf) Typical value for Asbestos 

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There have been few important advances in this area during the past year. The first crystal structure of a phosph(m)azene, Bu (Me3Si)NP=NBu, has been reported, and the claim made last year, of the formation of a compound containing a phos-phazene linkage which forms part of a four-membered ring, has been shown to be erroneous. The formation and properties of cyclophosphazenes (mainly amino-derivatives) and the phosphazene polymers have been reviewed. The patent literature is the most important growth area, particularly where flameproofing applications are concerned. 

Selection of fans and ducting for local extract must be more rigorous than for other systems. The fan must be capable of withstanding abrasion or corrosion from the contaminants, and if they are flammable must have a flameproof or out-of-air stream motor. The ducting also must be able to withstand abrasion or corrosion and must be fully sealed to prevent escape of contaminants within the building. For specialist applications such as fume cupboard extract, ducting and fans are often of plastic construction. 

Finally, it must be pointed out that all explosion protection devices or systems used in practice may be used only when their pressure rating, flameproof, and functional testing have been proved by competent bodies and their test results including the limits of application are documented in a type test certificate. 

Another group of chlorinated hydrocarbons comprises those made from paraffin wax. Major applications are in extreme pressure lubricants and as extenders and plasticizers in surface coatings and in vinyl plastics. The chlorinated waxes were also widely applied in flameproofing cotton fabrics, which led to large consumption by the military. It is believed that current military requirements for flame-resistant fabrics will be met by vinyl sheeting of vinyl-coated textile products, so that the World War II demand for the halogenated waxes will not be repeated. 

The gas theory is obviously not capable of general application, since many excellent flameproofers -- for example, titanium-antimony oxide mixtures -- do not evolve gases on heating. The theory has been criticized as unten le (20), based on the amounts of gas produced. Nevertheless, the gases produced are worthy of careful study as contributing in a subsidiary manner to the flameproofing of cellulose. 

TGL 30042 has defined a four-zone concept for areas hazardous due to combustible gases, vapours and mists EG 1, comparable with zone 0 EG 2 and EG 3, covering zone 1 EG 4, comparable with zone 2. In contradiction to the majority of standards covering the zone 1 requirements with all types of protection such as flameproof enclosure, increased safety, pressurization, oil immersion, intrinsic safety, powder filling, EG 2 excludes the general application of, e.g., increased safety e, which has been the domain of EG 3. 

Power supply for intrinsically safe circuits, category ia, for mining application, flameproof enclosure, terminal box in increased safety on the line power side ... 

Apart from inserting the complete gas analyser into a p-enclosure, the analyser head may be explosion protected for zone 1 application (e.g. according to flameproof enclosure - d - ) on its own, whereas the central control unit may be installed in a non-hazardous area, or alternatively, in a pressurized enclosure (Fig. 6.25) when zone 1 installation is required. 

In many cases there will be a certain demand for protective coatings (paints) against corrosion for the joint surfaces. This question should be handled very carefully. Many coatings contain particles (e.g. aluminium) which may adversely affect the flameproof properties of the joint. Tests should be made to ensure the coating s appropriateness for this application. 

Plug-and-socket connectors, cable couplers, see Fig. 6.81. These parts are inserted into an opening of the flameproof enclosure and act as a flameproof seal. This also applies to the unplugged state of plug and socket. Such means are favoured where apparatus is frequently removed, e.g. in coal mines (Group I application). 

In the second case, the bearings are exposed to the environmental atmosphere, i.e. they are no longer a part of the flameproof enclosure. They shall comply with the temperature limitations according to the temperature class. So, this solution is adequate for Group I application and for Group II, classes T1-T3, sometimes even for class T4. Table 6.31 indicates a somewhat higher weight of flameproof motors in comparison with e - or non-explosion... 

Frequency convertors for motor drives with variable speed have shown reliability and cost reduction for some time. An example for application in coal mines is shown in Fig. 6.104. A frequency convertor with impressed current in the DC link is installed in two separated flameproof enclosures ... 

Figure 6.109 Flameproof switchgear for Group I application, with SFe power circuit breaker.

Flameproof luminaires open a wide range of applications, based upon the fact that all types of lamps - with the exception of sodium vapour low pressure lamps - can be used (see Table 6.23, Section 6.7.4), especially those with ... 

Nevertheless, there are some aspects which will preserve a certain field of application for flameproof apparatus ... 

Obviously, type of protection flameproof enclosure - d opens a wide range of applications for zone 1 equipment. But it should be mentioned that... 

The selection of apparatus according to the data of a gas/the gases (explosion Groups I, IIA/B/C, temperature classes T1-T6) does not differ from rules valid for e.g. flameproof enclosure - d For normal zone 1 applications, category ib is sufficient. For circuits in zone 0 only, category ia shall be selected. 

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