Cfficer

1700 Tanker and uplift pump in attendance to remove 4600 gallons of petroleum from Tank No. 4. Nitrogen being introduced as tank emptied, through vent pipe of tank. 2245 Explosimeter readings taken in manhole in office of Elf Station 100% on 100% scale. 2315 Site left safe - note 4200 gallons already uplifted from Tank 4. Thursday, 24th February, 1977 0850 Work commenced on pressurising Tank 4 with nitrogen 1100 Staff report loss of 110 gallons

N. B 1445 1630 1830 2000

on Tank 6 showing on hydro gauges on reading taken on day previous, leakage of petrol and water noted in'to manhole of Tank 6 from surrounding area. Rodding of all drains instituted. Pressurisation of Tank 4 ceased as leakage of nitrogen pronounced on gland connection. After problem with gland connection to Tank 4, distortion of offset fill pipe during correction of leakage by contractors, leads to situation wher e nitrogen pressure test just no t pr acticable now without replacing off set f i ll line now too badly damaged to be left in-situ. Pe t r oleum tanker in attendance with uplift pump to r ecover 1600 gal lons of s pirit from Tanks 5 and 6 and 2000 gallons from Tank 2. Nitrogen being introduced to tanks thr ough vent pipes . Contractor wishes t o cut away f ore court t o replace dis tor ted offset f i ll to Tank 4. Pr oblem now i s hoW to r e nder empty tank safe whi l st concre t e r af t lifted above offset f il l l i ne. Se nio r Fire Prevention Of ficer on s i te advises local fi r m s pe ciali sing in degassing o f tanks shou ld be c alled in by contractor so t h at Tank 4 may be rendered s afe enough for excava tion work in clos e proximity bearing in mi nd l e akage o f pe trol eum to have occurred and the undes lrab i lity o f f i lling tank wi th water in view of t he known wate r pollution problem a lready. Friday , h 25t Februa r y, 1977 0900 Pr e ssurisation o f Tanks 5 and 6 with nitroge n in progress , leaks to e lbOW of inle t of offset fi l l c aps d · l S covered , pressur i sat . ion -discontinued s ince the r e will be ne ed for excavation round manhole to effect seal on offs et fi l l s . 1000 Site meeting between Senior Fire Prevention Officer, Contractor and Chief Engineer for Elf Oil (G.B)

Ltd., to discuss situation and ongoing safety measures on and around site. 1800 Tanks 1 and 2 on test with nitrogen at 10 lb. p.s.i

Saturday, 26th February, 1977 1015 Fire Prevention Officer on site specialist firm degassing Tank 4 with air remover.

Suction line to Tank 1 on test and proved satisfactory after tightening glands. Excavation of offset fill to Tank 4 commenced under supervision specialist firm remain in attendancE with air remover to maintain safe state of tank during uplifting of concrete surround. Concurrently work in progress on uplifting suction line to Tank 4, which proved to have significant leakage potential in riser and at elbow joint. This revealed on examination to' be resuit of extremely poor workmanship in that threads on the male coupling pipe had been eroded before fitting so that only three threads actually made seal and these were loose on removal (see diagram). 1800 Fire Prevention Officer back on site to check Tanks 1 and 2 on test from previous day at 10 lb. p.s . i . Test result satisfactory . Sunday, 27th February, 1977 0930 Explosimeter readings taken on si te. 1300 Further explosimeter readings taken . Pressurisation of Tanks 4,5 and 6 now with lines and offset fills repair ed in progress . 1730 Tanks 4 ,5 and 6 all at 10 Ib p.s .i checked and sealed.

Monday, 28th Februar y , 1977 0900 On si t e - explosimeter r eadings taken. 1715 On s ite . 1730 Tanks 4, 5 and 6 t aken off 24 hour Ni trogen Test . Tank 4 - Satis fac t or y Tank 5 - Sa ti s factor y Tank 6 - 2 .3 l b . drop - cont ractor bel i eves vent pipe l ett ing-by .

Elf Chi ef Engineer asks f or f urther t e s t on Tank 6

1815 Strong smell of petroleum spirit again in manhole in office explosimeter readings show rich mixture 100% on 100% scale LEL.

Tanker begins to uplift 4500 gallons of petrol from Tank 3 to discharge into Tank 1 and 2. 1930 Left si te .

Tuesday, 1st March, 1977 0900 On site - explosimeter readings taken. Decision taken to test Tank 3 and Tank 6 for second time. 1540 Tank 3 suction line on test to 10 Ib p.s.i - satisfactory 1715 Tanks 3 and 6 on test . Interceptor cleared out and river area by outflow pipe being cleared out.

Wednesday, 2nd March, 1977 0850 On site -explosimeter readings taken. 1715 On site - Tanks 6 and 3 found satisfactory at completion of 24 hour Nitrogen pressure tests

Thursday, 3rd March, 1977 0850 Explosimeter r e adings taken. 0930 Site meeting Divisional Fire Prevention Officer, Chief Engineer

Elf Oil (G .B.) Ltd., and Area Manager Elf Oil (G.B.) Ltd., to discuss reopening site for sale of petroleum. I t was agreed that site could reopen subject to regular clearing of interceptors at frequent intervals. Since it was now felt that petroleum spirit in sub soil on this site would seep into interceptor s through walls when level of content within lowered: in addition it was strongly recommended that contrac tor s overhaul all drainage on this si t e.

Friday, 4th Mar ch , 1977 0900 On s i t e -explos imeter r eadings s t ill signif i cant in of fice manhole 60% on 100% s cale . Readings at r iver out fl ow nil.

Station opened for s ale of pe troleum 19 days after problem first drawn to attention of Licensing The second i ncident at a garage in Bletchley in t he North of Buckinghamshire, proved to be no l ess troubl esome to the Inspecting Officers of the Brigade al though it is not intended to deal extensi vely with the ongoing problems with this particular incident except to state that subsiding clay at the infill site on which the Filling Station has been built, distorted and punctured no less than five of the 6 suction lines to tanks on the Station leading to a leakage of not less than 100 gallons of petroleum into the sub-strata. At one time, gulley emptiers of the District Council were being employed to uplift petroleum spirit seeping rapidly into an electric cable duct manhole from which the supply was piped to the mains electrical panel for the garage buildings. After extensive site works during which, of course, the Filling Station was closed to the public, the Station was allowed to reopen. In each of the above cases, there was known to have been extensive leakage of petroleum spirit into the soil under the Filling Station forecourt and in the second incident some strong evidence to suggest that the petroleum ·rit would Spl . remaln ' ln a lso ' d 1 1 c ay trough wi thout lateral movement. Attempts in each case t 0 get voluntary agreement of the , companles concerned to t excavate extensively in order to recovery of the leaked , 't me t Wl splrl , I t hough less than an enthusiastic success : a , asslstance in the second case , wlth some ' h fire 'I nd Wlt a from the District Councl a d t o t was ma e crew standing by , an at temp level pierce a " retalnlng 11 wa at a lower what in the clay infill site to r elease was supposed to be an d of water an tremely l ex troleum, pe f arge ly on concrete to be faced with several fee t 0 d behind the brick wall when pierce . the , ' that ex tent My questlon lS , 0 W , 't spons1ble Licensing Authorl Y re are for have the spirit below the site once theYthat taken all , posslble s t eps to ensur e d the site the leakage has been corr ect ed an d . of license again safe f or the stor age spir it? Is i t, as some of my have suggeste d a t a r ec t B en r anch Meetlng at Slough , enough t hat the s our ce of d leakage has been di scove r d nd e a corre cte , at no little expens e to the Licensee, have we a much stronger mor al respons 1 1 to ensure t hat every attempt i s made to recove r t he lost spirit before it comes up s omewhere else f a ter h vy ea rainfall,

possibly with serious ces consequen ? . If this l atter is the answer on what legal powers could we base our , ent requlrem , for the to sink borehol es untl1 the rogue spirit is locate d? I am sure some of you will have some to the questions and if you feel strongly enough , perhaps you will wr ite to the Editor f or inclusion in the next edi tion .

PLANNING AND THE PETROLEUM

OFFICER A Paper given by W.C.H. Dale Esq F.Inst Pet to S.E. Branch on 12th November 1975. Mr. Dale is an Honorary Member of the Association and Principal Clerk in charge of Petroleum Branch of London Fire Brigade.

I was invited to repeat today a talk which I last gave some five years ago to the Northern School of your Association. If I had done just that you would have been left wondering where I had been for the past five years. At one time I used to give the talk once or twice a year . Even 'then I notice that the script required up-dating on every occasion. You can imagine the changes that are necessary after five years . The basic principles, of course , remain the same. It is the methods that alter so considerably. I have always believed that a petroleum officer plans installations to secure t hose objectives. Firstly he aims to prevent ignition of the heavy inflammable vapour which is given off by petroleum s pirit and mixture. Secondly because he can never rely on there being no igniti on he must t ake measures to limit the extent of any fi r e and to minimize the r isk to persons. The thi rd objective is 1 ec t h os is l y is associated with the first two and ' t he preven tion of outflow. It is o use providi ng a safe area in pursuance n f the o . "t Sp1r1 f t he two aims if liquid petroleum and mixture is allowed to flow out area the mome n t any thong goes wrong. h ave been many fires where failure to pre ev nt . ou tflow has been not only the f lc ause 0 "gn ition but also of the serious damage suffered . I t i s worthwhile examin i ng the three ob j ec . t1ves i n some depth . PREVENTION OF IGNITION " fir Turn1ng " t h re a s tly re on to pr e or evention of two fac t s wh ich ignit10n e . tablish in our ID1nds. These ar e we should eS d are no doub t well known t o tary elemen. an · re of such importance that you but they . 1 a be done 'if we reitera t e them no harm w11 that " . t the inflammable It 1S no b t only the vapour burns u. the liqUld. The v liquid . . Wh1Ch 1S . apour wlll glven off .t i s mixed with air in the burn only 1 tright propor 1 'on 1 S . In respect 0 f . any iiquid the range of " i s known as the explOS,l ve 11m3, ts of th at liquid; (a most misleading term and one which the Americans more rightly call the limits of flammability). If a vapour concentration is below the explosive range it will be too weak or lean to burn; above the explosive range it will be too rich to burn. The explosive (or flammable) range is normally expressed as a percentage of vapour present with air by volume. Upper and lower limits of the range are always given. For petrols the range extends from about 1% of the lower end to about 8% at the upper end, for acetylene it is much wider from about 2.5% to 80%. The fact that we 'have an explosive concentration does not mean that we automatically have combustion. For ignition to occur, the vapour at any point in an explosive concentration must be to its auto-ignition temperature; this temperature for petrol is about 3000C. The extent to which vapour is warmed by any given heat source is of course a function of the temperature of that source and time. In Simple language this means that a source having a above 300oC. will ignite petrol vapour much more readily than one barely above 3000C. In fact if the source is very barely above 3000C., ignition may not Occur at all because convection currents may preclude vapour remaining sufficiently long in contact with the source for the vapour to be warmed above its auto-ignition temperature . Having said that, I must make it clear that 3000C was a nice round figure of the usual order which I selected for illustration purposes. Some petroleums have auto- ignition temperatures as low as 250oC .

Examination of t he facts we h ave so far discussed outline certain paths which we may fol low in pur suance of our fi r st objective . The first obvious step is t o ensure that we never ge t an explos i ve concentration of vapour. Obviously it i s undesi rab le to aim at t oo r i ch a mixture, i f for no ot her reas on than t hat above 0. 75% concentrat ion with air petrol vapour is toxic . Theoretically from a fire risk aspe c t we should aim wher ever p'ossible to keep any

concentration of petrol vapour with air below 1%. In practice to give a wider margin for error and to avoid gassing everyone a much lower concentration is sought.

Ventilation

This brings us to the question of ventilation. It is essential if we are to avoid the build up of an explosive concentration of petrol vapour and air that we should have good ventilation. The simplest and most effective way of ensuring good ventilation is to arrange for all storages of petroleum spirit and petroleum mixture to be in the open air.

There will, however, be occasions where considerable quantities of petroleum spirit or mixture are being evaporated and mechanical ventilation is required. In designing the mechanical ventilation system it· lS worth remembering a few simple facts. The amount of vapour which one volume of liquid will produce at normal temperature and pressure is equal to 22,400 multiplied by the specific gravity of the liquid and divid d b 't e y 1 S molecular weight. We can obtain the specific gravity from a reference book. To obtain the molecular weight we merely add up the atomic weights of the elements of the liquid.

Let us consider pentane which has a formula C5H12. The atomic weight of carbon is 12 and hydrogen 1. Therefore the molecular weight of pentane is (12 x 5) + (1 x 12) or 72. Its specific gravity is given as 0.63. Thus it follows that the vOlume of pentane liquid will give 22,400 x 0.63 772 or approximately 200 volumes of vapour at NTP. We know that 1 gallon occupies 4/ 25 cubic feet and can then say that 1 gallon of the liquid will produce 4/25 x 200/ 1 or 32 cubic feet of vapour By introducing a given qunatity of air to mix with this vapour we can have what concentration we fancy. Let us consider a plant in which! pint of our liquid is evaporating per minute , in a stoving enc losure. This means that 2 cubic fee t of vapour is being r eleased per minute. If we intr oduce 198 cubic feet of f r esh air per minute we will produce a 1% concentrat ion provided we ensure good mixi ng. Obviously this concentration is too high from a toxicity poi nt of view. Although below the normal lowest explosive l imit it is still too high from a fire risk of view - it should be reduced by at least a half and what is more the fresh air input should be monitored. Considerable further improvement would be required before people could work in this atmosphere. In fact one would aim to have those persons standing in the fresh air stream with contaminated air moving away from them; this is what happens with a spraying cabinet.

- -One final little point on ventilation before we move on. Do not fight nature unnecessarily. The vapours of all petroleum spirits are heavier than air and hence fall to the ground. In designing, extraction systems therefore arrange to pull from low level and place fresh air inlets at high level. Let gravity help you. On the other hand if you are dealing with hot vapour or vapour which is lighter than air then the opposite applies and you would arrange to extract from high level. Exclusion of ignition sources The next step in our fight to prevent ignition is to avoid the. . . . ' ource presence of any 19n1tlon s . . oncentratlon an area whre an explOSlve c . t But flrs of vapour is likely to occur. . h' h we have ln we must state the area w lC r the realms mind and here we really ente Office of . practlcal l po · t· lCS. The Home as being Code defines the danger area in the within 8 feet of a can store 1 f t of petro open air and within 14 ee . . l' statl.ons . measuring pumps on fll l.ng 11 the overa In certain locations where t risk is high by virtue of the amounxposure 'derable e stored and there is consl. . t' g depot, d' trl.bU l.n for example, at a bulk l.S 20 or 50 the distances are to the depot. feet; depending on the Sl.ze of

Ignition sources b ' ng . ces as el. Accepting these dl.stan 'd what are reasonable we must cons1 er some . There are l1kely ignition sources. . and flame, obvious ones such as fl.re These lighted Cigarettes as so our obviously should be excluded d u will know selected danger area, an yo . . k s provl.Sl.on that the Home Offi ce Code ma e for this . However The Codes 1 --0 a s i;;'cl ude a . . slml.lar pr ' " ohibitl.On n l. respect of electric light electrical apparatus , . ' or appllance l ikely vapours . Inclusion to of .' t l.gnl. e the inflammable kd 'likel'" indicates that discretion is called for. It is in the field of the exercise of this discretion that the most outstanding changes have taken place in recent years. The last time I gave this talk every country in t he world had its own local rules . To some extent they still do but at least considerable strides are being made towards internation al agr eement .

The base document, if I may call it that, is Publication No. 79 bf the International Electrotechnical Commission. The Publication comes in various parts each dealing with a particular concept or method of protecting electrical equipment. Member countries of the Commission are gradually re-writing their local standards to accord with this international standard. The British Standards Institute is heavily engaged on this task at the present time. This is evidenced by the emergence of a continuing number of parts of British Standard 4683. Also there are in existence a number of drafts to replace the various parts of British Standard Code of Practice 1003. All this is making life very difficult at the present time but in the long term the ends of simplicity may well be served.

Danger Once upon a time we split danger areas into 'Divisions'. To accord with international practice, which incidentally is British inspired we should in future refer to Zones.

Zone 0 area

It i s necessary that we should define r Zones and we run into a minor ou difficulty. . ' Defin1.t1.ons 0 f 't necess1. y come 0 ut in black and white terms , whereas , , tice one is always deal1.ng w1.th 1.n Wac , shades of grey. Thus the varY1.ng . " h ' 'tions must be appl1.ed W1.t a def1.n1. . d ' t 11' f common sense an 1.n e 1.gencedegree 0 , . It , 1.S f or this reason that I l1.ke the ach which the Institute of Petroleum appro, is adopt1.ng. They firstly define a atmosphere as being an atmosphere dangerouS taining con y signi ficant an s or vapour in quantity of a concentration The use of the word capable ble' 'capa I , my 1n the opinion blurs old days Zone the edges 0 was nicelY· nb ing an area or enclosed space f ' ed as e de 1.n ' h any flammable or explosive 'thin wh1.C W1 e whether gas, vapour or substanc " 1.'d is continuously present 'le ll.qu . volatl. tion within the upper , nce ntra 1.n co . of flammability. In liml. ts lower re were Smart Alecs who and the , sa1d, res ul t the, this defini tion s trictly , interpretatlng trol tank was not Zone 'd a pe that ins1. e otly the atmosphere was e freque o becauS· the upper explosive . h nd above too r1C a Id not, however, be l ""t They WOU 1m2 . that there was not a able to argue h t k They dangerOus at mosphere in t e an " would thus have to concede that Zone 0, when defined as an area in which a dangerous atmosphere is continuously present, includes the inside of a petrol tank. Zone 1

Following on from this definition one would define Zone I as an area in which a dangerous atmosphere is likely to occur under normal operating conditions. You are all familar with the Home Office Model Code so there is no need for me to illustrate the type of area in mind. Zone 2

Beyond the Zone 1 area lies the Zone 2 area and this would be defined as an area in which a dangerous atmosphere is likely to occur under abnormal operating conditions. Safe areas

All areas which are not classified as dangerous areas are termed 'safe areas' . -Certiflcation System Having decided by use of the definitions the zone of a particular area we are faced with the problem of what electrical apparatus to allOW in the zone. Sensibly we will whenever possible avoid the use of electrical apparatus in any dangerous area but there will be many occasions when it will not be possible to apply simple s-traightforward common sense rule. To help us in our task we have the British Approvals SerVice for Electrical Apparatus in Flammable Atmospheres (BASEEFA) which is now part of the Health and Safety Executive. They have a trade mark which may go only on such apparatus as they have certified. This consists of the letters 'Ex' in a crown. Under the terms of the Treaty of Rome we will in due course have to accept t he certification of other Common Market countries but for the time being until Government directs otherwise I would sugges t that for general application you accept in dangerous atmospheres only suitable electrical equipment certifi ed by BASEEFA. In the case of specialized equipment you may exceptionally be prepared to admit the certification of another country but I suggest that you should do this only if the country is a member of the International Electrot echnical CommiSSion and there is clear indication that the apparatus complies with the appropriate Part of the lEe Publication No. 79 .

Grouping of apparatus For the purpose of certification, electric apparatus is classified into two basic groups i.e., Group 1 and Group 11. Group 1 apparatus is for coal mining and Group 11 apparatus for industries other than coal mining. You will mainly be concerned with Group 11 apparatus. Apparatus in Group 11 is sub-divided into three sub-groups: Group llA, lIB and llC according to the characteristics of the gases and vapours which the apparatus is suitable. The h1ghest standard is llC and accordingly used for type llA or lIB vapours. Slm1larly lIB apparatus may be used in llA atmospheres. However lIB apparatus may not be used in llC atmospheres nor may llA be used in either lIB or lIC For petrol vapours llA 1S the appropriate classificat1· on.

Temperature classification

We earlier the importance auto-1gn1t10n temperature. Obviously would be madness to install in a atmosphere any electrical equ1pment which had surfaces hotter than the aut o-ignition temperature of the vapour exposed to that vapour. So we require a marking Code as follows:-

Tl not exceeding 450 T2 do. 300 0

T3 do. 200 0 0

C C T4 do . 135 0C e T5 T6 do. do . 1000e 85 0 C

The temperature classificati on for certified equipment ambient temperature is of based .400 e . on an In hot locations wher e this ambient is exceeded the surface temperatur e of the apparatus may be higher than the sge cified limit . Thus may a in an ambient of 70 chieve 200 + 30 or 2 C, 30 0T3 e . apparat T3 is us SUitable for most petr ol vapours and the mar king on t he appar atus would appear as T3 (2000C) . Rather annoyingly i t is pe r mitted for apparat us to be marked wi th t he actual temperatur e achi e ved i n which case you might see 2l0 0 C (T2) . (Why do people always insist on intr oducing t hese unnecessary complicat i ons ? ) .

Fl ameproof enclosure - concept ' d ' We can now conside r the var ious concepts and the first mus t be f amilar to you all . This is the fl amepr oof concept . Flameproof eqUipmen t is in no sense vapour tight but is so designed that it can withstand an explosion within its housing and yet not transfer to the external atmosphere sufficient heat to ignite an explosive concentration. Safety is dependent both on suitable over-current protection and the maintenance of flame path dimensions. The international symbol for flameproofing is the small letter 'd'.

Increased safety concept 'e' The concept of increased safety is comparatively new to this country and can be applied only to electrical apparatus which does not spark or arc or exceed vapour ignition temperature. Special emphasiS is placed on quality of construction and materials , connections which cannot work loose, clearance distances and creepage distances between conducting parts as well as on limiting termparature which in some cases is achieved by thermal overload devices. In other wordS if you can quarantee no sparks or hot spots then you can have no ignition. In this connection I should mention in passing. that the safety of increased safety motors 1S very dependent on the correct use and. selection of an appropriate star t e r , 1f you are not expert in this field of . electrics you should obtain expert adv1ce . The international symbol for increased safety is the little letter ' e' .

Intrinsic safety - concept ' i ' In my opinion the t concep f 0 intrinsiC safety has been debased recently. The basic . idea· 1S s t · 11 1 that it is .. possi 0 ble limit 1n certain parts of a c1rcu1t to s the current and voltage that should a fault occur and a spark resul t , the energy of the spark will be so l oW a s to be incapable of igniting petr oleum spiri t vapour. No longer, however, is t her e a singl e class . We now h ave two . The international symbol f or i n t r i ns iC . safety is l ittle 'i ' . I f a li t tle ' a' 1S added t o this i t means t hat . the . int egr . ity th of the apparatus wi ll be ma1nta1ne d W1 up to two faul ts . If little 'b ' is added only one faul t at a time is consi dered. Thus 'ia ' is a h igher standard t han 'ib' .

Once upon a t ime we had on ly intri ns ically saf e circuits and equipment but now we have intri nsical l y saf e syst ems as we ll. This has been brough t about by the de ve l opment of spec ial ized type s of electric al barrier s, such as Zene r diode barr i e r s . Through these barrie r s for example an intrinSical l y s a f e pu lseI' inside a pump can be coupled t o a computer i n a s afe l ocation miles away . The simp l e trick of putting bracke t s a round t he' i a' o r

'ib' symbols is used to indicate apparatus which may be associated with certified intrinsically safe equipment. This ·associated apparatus must always be in a safe area.

When considering intrinsically safe apparatus always look at the BASEEFA certificate number. If you see the capital letter 'B' at the end there are special conditions to be observed and these you should obtain from the certification documents. If the letter'S' is at the end whether or not ot follows the letter 'B', you are considering associated equipment which must be in a safe area. Type'S' equipment There is equipment which is safe for use in dangerous atmospheres but which meets none of the foregoing concepts wholly although possibly incorporating bits of them all. Equipment of this type, such as fully encapsulated motors, for example, are certified specially and for this reason carry the international symbol little 's'. You may need to look at certification documents to determine the

Zone for which a particular piece of Type's ' equipment is suitable.

Type ' N' equipment The only other concept at present cer tified by BASEEFA is Type 'N'. This follows loosely the increased safety idea of no spark or hot spot accessible to vapour, but the means of achieving this are different and certainly . t o a significantly debased standard . IEC publication 79 makes no provision for Type N equipment . pressurized e qui pment - concep t 'p' lEC Publication 79 - 2 does however alloW pressur ized equipment , At t he present t i me t he r e is no British Standard and this type of equipment i s not cer tified by BASEEFA. I t fal ls to each enfor cement a uth ori ty to apply the provisions of British s tandard Code o f Practice 1003 : Part 2 . The b a s i c i dea is that i f a higher pressure than hat o f extern a l a t mosphere is maintain ed t 'thin the hous'f' f l n g 0 any plece 0 W2 tricelec 1 b e al e out quipment th of the equi e p n me f n l ow t an of d v air c apour an on c an Y t e n no st ter. be dr Obvious l awn from y a the p safe r ess loca uri zin tion a g nd

a ' r 1, mu. to s a f e devi ces mus t be fit t ed to fal l gise t he equipment should ther e be deener " . Th . o f the pre ssurl f a ilure Sion o f t his co an e x t en '1 t d hous ing meth ventl a e . with it. The bore you . zlng alr. ere l S ncept known as the . od bu t I wl ll not new symbol for pressuri zed equlpment i s little ' p '. Other concepts There are other concepts in IEC Publication No. 79, such as sand filling, but as these are not used in this country and as no comparable British Standard exists, we can skip the details. Allocation of equipment to Zones In Zone 0 one would permit only intrinsically safe ia (not ib) equipment. Pressurized apparatus might be permitted where the enforcing authority is satisfied with the arrangements. Type's' equipment would only be suitable if the certification documents so indicated.

In Zone 1 any Zone 0 apparatus would be acceptable and additionally flameproof apparatus and intrinsically safe ib equipment may be allowed. Increased safety equipment is suitable only if it is in a position where flammable liquid will not drip onto it if there is a pipeline or other fault.

In Zone 2 all the equipment mentioned above may be installed or alternatively Type N equiment may be used. Safe areas call only for standard equipment.

Special Petrol Pump Standard

Before finally leaving this very important question of electrical equipment in flammable atmospheres I should mention that BASEEFA have a certification standard SFA 3002 for petroleum spirit measuring pumps. The purpose of this Standard is to provide a means of certification for pumps which while not complying precisely with the Home Office Model Code are nevertheless safe for use on filling station forecourts, British Standards

If you wish to examine in greater de tail this whole question of electrical equipment in flammable atmospheres you can do no better than read the various BASEEFA publications and the various Parts of Standard 4683. You should also keep an eye on the revisions to British Standard Code of Prac tice 1003 as they appear i n the form B.8 . 5345. Thermi te react i on and static

In conside r i ng possib le ignition sources , this can i nclude such exotic as s t at ic and thermi t e r eac tion . But one has to stop s omewher e s o I do no t propos e t o deal with these aspec ts today . Nevertheles s i f questions ar i se in discussion I wil l be happy t o answer them.