Intrinsic safety 101 - UToledo Engineering

1 7 Intrinsic safety 101 protection methods, containment, segregation, and preventionBy Robert Schosker ' This article answers the question, "Why worry about hazardous locations?" The area classifica-|tions. for the and the European (the International Electrotechnical Commission [IEC] stan-|dard) approaches are described and contrasted, including protection methods, containment,segregation, and preventionWhat is Intrinsic safety ? Intrinsic safety (IS) has been around a long time. It is the concept of limiting ignition-capable energyto Below that of the hazardous material a process may be working with. IS, as most people callit, wasborn out of the ashes of a horrible roining accident in the in 1913.

2 The explosion was caused bySubstitute l! Operat r 1the dangerous Residual training/substances protection risk qualificationMinimize theRisk reducing bytertiary explosionprotection54 INTECH SEPTEMBER/OCTOBER 2013 ,ORGAUTOMATION BASICSa low-voltage signaling system that was used toadvise the surface crew that coal cars were readytO be brought to the surface. The ensuing re-search revealed that the most important factorin determining the safety of, an electrical circuitis the energy stored in the circuit. The conceptof Intrinsic safety was why do we worry about hazardous loca-tions?

3 Many explosions are the result of lim-ited knowledge by employees, which can bedirectly related to inadequate training, lackof documentation, and questionable safetymeasures. These disastrous results may havebeen prevented with proper training, new in-strumentation, inspection, maintenance, orrevised safety procedures. Of course, even ifthe plant takes these steps, an explosion couldstill happen; however, every effort to reduce"residual risk" is a benefit. Residual risk is therisk left Over after all other forms or mechani-cal means of risk reductions have been hazardous area is an area containing (orlikely to contain) an ignitable concentration offlammable gas, vapor, or dust, where an electri-cal spark of sufficient power will cause an ex-plosion.

4 However, an explosion can only occurwhen an oxidizer, the hazardous substance (gas,vapor, or dust), and energy (thermal or electri-cal) are present at the same time. These threegroups comprise what is known as the hazard-ous location ignition defines a hazardous location? What is thedifference between zones and divisions? Theseare all very good questions, and ones that areoften asked. We already know that a hazardouslocation is an area that contains of is likely tocontain an ignitable concentration of flammablegas, vapor, or dust. Once we have determinedthat a hazardous area exists, then we classify thatarea using either zones or divisions.

5 Although thephysical principles of explosion protection arethe same worldwide and are not differentiated,the procedures determined by national legisla-tion in the approximately 100-year history of ex-plosion protection have resulted in various solu-tions. Each solution has a unique perspective onhow to classify a hazardous ..I Class ; Division; Groups; T__Class (t-lit)(1-2) groups (x--y)Temp codes (T1-T6) , Oxidizer Fuel(air) (gas, vapor or dust)If any one of these groups is removed, anexplosion cannot happen. As we will discussthroughout this article, Intrinsic safety is amethod of protection that removes one of thesegroups from the ignition article will first answer some basic ques-tions about hazardous locations.

6 We alreadyknow why we worr but what are we worryingabout? What is a hazardous location? What orEnergy(thermal or electrical)Divisions, mainly a North American-approvedmethod of classifying an area, use four catego-ries: class, division, group, and are commonly seen like this:Hazardous due to the presence of flammable substances such as gases or vaporsHazardous due to the presence of flammable substances such as dusts orpowders. -Hazardous due to the presence of flammable substances in a flying categorization of these areas is carriedout in North America in accordance with theNational Electrical Code NFPA 70, article I, II, or III represent the form of the haz-ardous material you must deal can be present during normal functioning, during repair or main-tenance, or where a fault may cause the simultaneous failure of material is present but confined to a closed container orsystem.

7 Is normally vented or in an area adjacent to a'Division I is a categorization by the probabilitythat these materials will be present in a poten-tially hazardous quantity (Division 1 and Divi-sion 2). The division is commonly the perimeteror designated area of the hazardous SEPTEMBER/OCTOBER 2013 55 AUTOMATION basics Class I i GroupAGroup BI F rou Ci: Group D\Class Ii I Group EiGroup FAtmospheres containing acetyleneAtmospheres containing hydrogen and flammableprocess gasses with more than 30 percent hydro-gen by volume, or gases or vapors posing a similarrisk level such as butadiene and ethylene oxideThe graphical representation below illustrates the con-cept of division-based locationsMaximum temperature( C)450r30O280260230215200180i65160'135120 10085( F)

8 842572, 536500446419392356329320275248212185 Temperature classin North AmericaTIT2T2AT2BT2CT2DT3T3AT3BT3CT4T4AT 5T6 Furthermore, classes, of hazardous areas are divided intosubgroups depending i3n the type of flammable gas or apparatus installed directly in a hazardous areamust be' classified for themaximum surface temperature thatthe device will normal operation or in theevent of a fault, The maximum surface temperature must bebelow the minimum ignition temperature of the gas present,Atmospheres such as ether, ethylene, or gases orvapors posing a similar risk levelAtmospheres such as acetone, ammonia, benzene,butane, cyclopropane, ethanol, gasoline, hexanemethanol, methane, natural gas, naphtha, propane,or gases or vapors posing a similar risk levelAtmospheres containing combustible metal dusts,including aluminum, magnesium, and their com-mercial alloys, or other combustible dusts whoseparticle size, abrasiveness, and conductivity presentsimilar hazards in the use of electronic equipmentAtmospheres containing combustible carbona-ceous dusts including carbon black, charcoal,coal.

9 Or coke dusts that have more than 8 percenttotal entrapped volatiles, or dusts that have beensensitized by other materials so that they presentan explosion hazardAtmospheres combustible dusts notincluded in Group E or Group F, including flour,grain, wood, plastic, and chemicals: i GroupGKeyDivision IDivision 2 GradeSump or trench In Europe, the zone method of area classification is European zone practice is described in IEC/EN 60079-10. In accordance with this standard, any area where there isa probability that flammable gas or dispersed dust may existmust be classified into one of the following areas:Zone 0 Zone 1 Zone 2 Zone 20 Zone 21 Zone 22An area !

10 N which an explosive airlgas mixture is continu-ously present or present for long area in which an explosive airlgas mixture is likely tooccur in normal area in which an explosive airlgas mixture is unlikelyto occur, but, if it does, only for short periods of time. An area in which a combustible dust cloud is part of theair permanently, over long periods of time, or frequently. An area inwhich a combustible dust cloud in the air islikely to occur In normal area in which a combustible dust cloud in the air mayoccur briefly or during abnormal European zones then require that the apparatus besubdivided into two groups, according to IEC/EN two groups in general terms indicate whether the ap-paratus is located ,above or below IGroup IIApparatus to be used in mines where the danger is repre-sented by methane gas and coal to be used in surface industries where the dangeris represented by gas and apor that has been subdividedinto three groups: A, B, and C.