REVIEW

Safety of chlorine productionand chlorination processes

1074-9098

doi:10.101

Most chlorine production is obtained by electrolysis of NaCl aqueous solution. Other processes to producechlorine involve the electrolysis of KCl or HCl aqueous solutions, the electrolysis of molten NaCl at hightemperature and the Deacon process. In most cases, chlorine is a by-product in the production of causticsoda, potassium hydroxide, sodium metal or is recovered from HCl using HCl aqueous solution electrolysisor gas–solid reaction in the Deacon process.

Chlorination reactions are part of various processes in the chemical industry, to manufacture heavychemicals, specialty chemicals, pesticides and pharmaceuticals, in inorganic and organic chemistry. Theyare valuable tools in organic synthesis.

The hazards of chlorine production and chlorination processes involve:

- Gas phase explosion, i.e., self-ignition, deflagration and detonation in the gas phase.- Runaway reaction or thermal explosion, deflagration and detonation in the condensed phase.

Gas phase explosion hazard with chlorine as an oxidizer is present in the production of chlorine byelectrolysis, in gas phase chlorination processes and in chlorination reactions carried out in the condensedphase.

Gas phase chlorination processes are continuous processes operating either in the flammable range likeburners or outside the flammable range in loop reactors or loop processes where chlorine is the controllingreactant.

When chlorination is carried out by chlorine injection in the liquid phase, gas phase explosion hazardis related to chlorine evolution in the vapour phase, giving a flammable mixture with the solvent orreaction mixture vapour. Hazard assessment is achieved by comparing the gas phase composition with theflammable area of the gaseous mixture. Self-ignition is also considered because the self-ignition temperatureof gaseous fuels in chlorine atmosphere is lower than in air or oxygen and often close to the ambienttemperature.

The relevant flammability data is the flammability limits, LFL, UFL, minimum oxidizer concentration(MOC), auto-ignition temperature (AIT), of fuels in chlorine and the explosion characteristics Pmax and KG

for deflagration in chlorine.A collection of flammability data is given for the reader convenience, collected in the literature or obtained

in our own experimental facility, a specially designed 20 L Hastelloy C 276 sphere with 200 bar pressureresistance, ambient to 300 8C initial temperature, easily opened for frequent cleaning. This apparatus allowsprecise determination of the flammability limits, self-ignition temperature, explosion overpressure, rate ofpressure rise and flame speed.

Runaway reaction hazards in chlorination reactions are related to a series of dangerous process situations

or process deviations such as:

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- Delay in reaction initiation.- Reaction mixture instability.- Production and accumulation of unstable species like chloramines, nitrogen tri-chloride, chloro-nitroso

compounds, alcohol hypo-chlorites.- Demixing or separation of unstable species in case of chlorination reactions made in aqueous solution,

because the chlorinated compounds are less soluble in water than the initial reactant.A full review of runaway reaction hazards in chlorination reactions is given with examples from theliterature and from the laboratory.

/$30.00 � Division of Chemical Health and Safety of the American Chemical Society 5/j.chs.2004.08.002 Elsevier Inc. All rights reserved.

By Jean-Louis Gustin

cess is used for the recycling into chlor- a condenser. In between is a grey zone

INTRODUCTION—CHLORINEPRODUCTION AND USE

Most chlorine production is obtainedby electrolysis of NaCl aqueous solu-tions. Different processes are alsoused. Their importance depends onthe area considered.

In 1996, the mercury cell processaccounted for 53% of the chlorine pro-duction in France, 64% in Europe and39% worldwide. The diaphragm cellprocess accounted for 32% of the pro-duction in France, 25% in Europe and45% worldwide. The membrane cellprocess accounted for 15% of the pro-duction in France, 11% in Europe and16% worldwide.

For environmental reasons, theinstallation of new mercury cell plantsis not allowed in Europe and the exist-ing plants must meet the ever moredemanding regulation for mercuryemission control. The importance ofthe diaphragm cell process shouldnot increase as long as diaphragmsare made of asbestos. New plants areusing the more environment friendlymembrane cell process.

The process for the electrolysis ofNaCl aqueous solutions to producecaustic soda may apply to the electro-lysis of KCl aqueous solutions as well,for the production of potassium hydro-xide.

For the production of sodium metal,theelectrolysisofmoltenNaClat650 8Cis used. This process accounts for 2% ofthe chlorine production in France.

The electrolysis of HCl aqueoussolutions using a diaphragm cell pro-

Jean-Louis Gustin is process safetyconsultant since 1984 within the for-mer Rhone-Poulenc, Aventis, and nowRhodia, working in the field of chem-istry and runaway reactions. He isaffiliated with Rhoditech 24 AvenueJean-Jaures, F69153 Decines-Char-pieu, France (Tel.: +4 72 93 57 14;fax +4 72 93 59 68; e-mail: jean-louis.-gustin@eu.rhodia.com).A short version of this paper was pre-sented to the Eurochlor seminar heldin Leipzig, Germany, 1997, and waspublished by Eurochlor under thereference GEST 97/242.

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ine of HCl aqueous solutions producedby chlorination processes. The HClproduced by TiO2 chlorine processesmay be recycled into chlorine using theDeacon process.

The chlorine produced by electroly-sis of NaCl, KCl, or HCl aqueous solu-tions is obtained wet of water and iscorrosive for current metallic materialsof construction except titanium. Thewet gas is dried as soon as possibleby cooling to above 12 8C to preventchlorine hydrate formation, often bydirect contact with cold water, filtra-tion of the water aerosol and washingwith 98% sulphuric acid in a column,to reach a water concentration of lessthan 20 mg/kg chlorine. Then carbonsteel equipment dried to a dew point of�40 8C under atmospheric pressuremay be used to process dry chlorine(see Process diagram 1).

The dry gaseous chlorine is thenwashed with liquid chlorine in a bub-ble-cap tray column operated at�35 8C under atmospheric pressureto remove nitrogen tri-chloride fromthe gaseous chlorine and cool the gasbefore compression. This column isalso intended to separate chlorinatedorganic compounds from gaseouschlorine before compression in plantswhere this chlorinated organic con-centration is significant (see Processdiagram 2).

NCl3 and the chlorinated organiccompounds condense or dissolve inliquid chlorine in the column bottom,which is routinely admitted in aso-called re-boiler where carbon tetra-chloride is often added to extractnitrogen tri-chloride and allow its sub-sequent disposal/destruction. Carbontetrachloride is a suitable solvent toextract NCl3 because it cannot befurther chlorinated and has an atmo-spheric boiling point of 77 8C versus71 8C for NCl3.

The re-boiler is intended to allowchlorine to vaporize and return tothe column.

The re-boiler is either operated cold(0 to5 8C) inwhich caseNCl3 is allowedto accumulate in this vessel and must befurther disposed, or the re-boiler isoperated hot (45 to 60 8C) in which casethe re-boiler is intended to thermallydecompose NCl3 and is equipped with

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where the temperature is not carefullycontrolled, allowing NCl3 to accumu-late and subsequently decompose. Thisprocessing step is subject to many pro-blems and accident case histories con-cerning the disposal/destruction of theNCl3 solutions.

The gaseous chlorine is then lique-fied by compression and cooling thusproviding a further purification step forthe liquid chlorine and allowing thestorage and transport of liquid chlor-ine.

Total liquefaction of the chlorineproduced is difficult and may causeproblems due to the presence of gas-eous impurities (H2, CO2, CO, O2, N2).A fraction of the chlorine production isnot liquefied and is used on site at leastfor the production of bleach. This gas-eous chlorine is rich in gaseous impu-rities and called residual chlorine.

The chlorine consumer plants arebest situated near the chlorine produc-tion plants, to limit chlorine transport.However, this is not always so for his-torical reasons or for small consumerplants. Therefore, a fraction of thechlorine produced is liquefied toobtain good purity chlorine and allowchlorine to be transported to remoteconsumer plants. In France and inEurope as well, the capacity of liquidchlorine storage facilities is limited bythe regulation. In France, chlorine sto-rage vessels as well as loading andunloading stations must be enclosedin a housing connected to a scrubberusing caustic soda, to control acciden-tal releases. The capacity of the scrub-ber is typically 5,000 kg/hour chlorinein air destruction.

Most chlorine storage facilities areoperated at or near ambient tempera-ture, under the liquid vapour pressure.There are limited examples of cryo-genic chlorine storage facilities oper-ated at �35 8C and atmosphericpressure, as a buffer storage betweenchlorine production and local con-sumption. About 10% of the chlorineproduction is transported to a remoteconsumer plant. Bulk chlorine trans-port in Europe is by rail tanks. The useof road trucks is very limited. The useof barges or boats was considered innorthern Europe, it is more wide-spread in the USA.

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Process diagram 1. Chlorine line of an electrolysis plant.

One tonne cylinders and bottles areused to supply chlorine to small con-sumers and for water treatment.

Chlorine is an important rawmaterialin the chemical industry. The main usesare in the production of PVC (40%),chlorinated solvents (25%), Phosgene(10%), other organics (10%), inorganicand miscellaneous products (15%).

Quite similar to oxygen, chlorine isused as an oxidizer in a wide range ofchemical processes where it is reactedwith organic and inorganic com-

Process diagram 2. Washing/cooling colum

Chemical Health & Safety, January/Februar

pounds to produce chlorinated pro-ducts or intermediates. A wide rangeof useful products are obtained suchas bleach, metallic chlorides, reactivemonomers to manufacture plastics,heat exchange fluids, chlorinatedsolvents and intermediates in organicsynthesis to produce specialtychemicals, pesticides and pharmaceu-ticals.

Chlorine is involved in a wide rangeof process situations including gasphase reactions in a burner or in a loop

n and re-boiler.

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reactor, on a catalyst bed, solid /gasreactions in a fluid bed, gas/liquidreactions in a packed column, gas/liquid reactions by injecting chlorinein a liquid phase in a semi-batch pro-cess or in a continuous process. Thereaction of chlorine takes place with-out catalyst, in the presence of a cata-lyst or in photochemical reactions.

Compared to oxygen, chlorine is amore reactive gas because it is pro-cessed as a pure gas whereas oxygenis often reacted using air. More pro-blems would occur with oxygen if theuse of pure oxygen was widespread inthe chemical industry.

Compared to pure oxygen, chlorineis even more reactive. The self-ignitiontemperature of gaseous mixtures oforganic vapours with chlorine is muchlower than that of their mixtures withoxygen. Natural light can split thechlorine molecule to produce reactivechlorine radicals. Many reactions ofchlorine take place near the ambienttemperature. The combustion of ironin chlorine can be initiated at tempera-tures slightly above 100 8C.

Chlorine is toxic to man and ani-mals. Many chlorinated compoundsare also toxic.

The TLV�TWA is 0.5 ppm and theSTEL/C is 1 ppm. The effects of expo-sure to chlorine may be described asfollows.

Below 1 ppm, detection of the smell bynormal subject.

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1 to 5 ppm, slight irritation of the upperbreathing path.5 to 8 ppm, irritation of the upperbreathing path and of the eyes.15 to 20 ppm, immediate severe irrita-tion of the upper breathing path, strongcough and choking.30 ppm, breathing is difficult, pain tobreast, nausea, vomiting.40–50 ppm, chemical tracheobronchi-tis, severe lung edema may appear upto 72 hours later.Above 50 ppm, depending on theexposure time, loss of consciousnessand death.For all the above reasons, the chemical

processes where chlorine is involvedare submitted to careful safety studieswhere the specific chemical propertiesof chlorine are considered.

THERMAL EXPLOSION HAZARD INTHE CONDENSED PHASE

Chlorine is a strong oxidizer. Mixturesof chlorine and organic fuels may havea high energy content and are unstable.The thermal instability of condensedphases containing chlorine can appearin various process conditions.

Example of Chlorine Accumulation Dueto a Delay in the Chlorination ReactionInitiation

When chlorine is injected in a liquidreaction mixture, the chlorinationreaction may not start immediatelyallowing chlorine to accumulate inthe reaction mixture. The reactionmay start suddenly when a large con-centration of chlorine is present in thereaction mixture and give a severe run-away reaction producing a large quan-tity of insoluble HCl. An example ofsuch an induction period in chlorina-tion is mentioned in the literature forthe chlorination of ketones in metha-nol.1 To avoid this type of incident, thereaction onset should be checkedbefore allowing a large concentrationof un-reacted chlorine to be dissolvedin the liquid phase.

Examples of Dangerous ProcessSituation in Chlorination Reactions

When chlorine is reacted with anorganic fuel in a liquid reaction mix-ture, highly unstable substitution pro-

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ducts may be obtained. This processsituation is dangerous in two cases:

- if

a high concentration of unstablechlorination product is obtained inthe condensed phase and

- if

a chlorinated liquid phase sepa-rates from the bulk liquid phase‘‘by segregation’’.

The latter situation is frequent in the

chlorination of aqueous solutions oforganic reactants because the chlori-nated products are less soluble in waterthan the initial reactants.

Examples of this dangerous processsituation are the synthesis of alcoholhypo-chlorites by injecting chlorine inan alkaline aqueous solution of alco-hol, the formation of nitrogen tri-chloride by chlorination of certain‘‘dangerous’’ nitrogen containing com-pounds, the chlorination of oximesin aqueous solution, the radical orphotochemical chlorination of succi-nimide.

Alcohol Hypochlorites

Traugott Sandmeyer described thesynthesis of methyl and ethyl hypo-chlorites2,3 and suffered severe injuriesdue to explosions during the experi-ments. In Sandmeyer’s method toobtain alcohol hypochlorites, chlorineis injected into an aqueous solution ofalcohol and caustic soda with a moleratio alcohol/sodium hydroxide of 1,under cooling at 0 8C. The alcoholhypochlorite separates by decantation.When chlorine does not dissolve anylonger in the solution, chlorine injec-tion must be interrupted to avoid thealcohol hypochlorite decompositionunder acidic conditions. The methodwas described for the synthesisof methyl hypochlorite and ethylhypochlorite. Methyl hypochlorite isa volatile yellow oil with a boiling pointof 10 to 12 8C under 726 mmHg. Ethylhypochlorite has an atmospheric boil-ing point of 36 8C. The liquids areflammable in air. They decomposeslowly under alkaline conditions andwith violence under acidic conditions.The Sandmeyer method may beapplied to water soluble alcohols.Roland Fort and Leon Denivelle4

described the synthesis and propertiesof a series of other alcohol hypochlor-ites obtained following Sandmeyer’s

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method and proposed other methodsof solvent extraction to obtain thosealcohol hypochlorites which cannot beobtained directly using Sandmeyer’smethod.

In most process instances, the forma-tion of alcohol hypochlorites isunwanted for process safety reasons.However, the formation of alcoholhypochlorites is possible in waste-watertreatments where alcohols are present,using chlorine or bleach. This is a veryfrequent process situation. The accu-mulation ofalcohol hypochlorite is pos-sible under alkaline conditions. Thesolubility limits of the hypochlorite inwater depend on the alcohol chainlength. Methyl hypochlorite is solublein water and should not separate unlessthe alcohol concentration in the wastewater is veryhigh (of severalpercents byweight). Under acidic conditions, alco-hol hypochlorites are unstable andshould decompose readily or behavelike chlorinating reagents, contributingto the water treatment. One should takecare if the yellow oil separates from thebulk liquid. Methyl and ethyl hypo-chlorites may detonate in the liquidphase.

Nitrogen Trichloride

The oxidation of organic compoundscontaining nitrogen in their formula(amines, amides, cyanides, urea) usingchlorine, gives unstable chloramines.The very unstable nitrogen trichlorideis finally obtained. NCl3 is only slightlysoluble in water and can separate fromaqueous solutions giving a very sensi-tive yellow dense oil. NCl3 can also beobtained by chlorination of aqueoussolutions containing ammonium ions,ammonium nitrate, ammonium sul-phate, ammonium chloride or ammo-nia. The formation of nitrogentrichloride is possible in chlorinationprocesses and in water treatment usingchlorine or bleach.

Due to the presence of ammoniumions and amine impurities in the salt,and to the use of nitrogen containingflocculants for salt processing or to thecontamination of the salt by dangerousnitrogen containing impurities, nitro-gen trichloride is present in the crudechlorine produced by electrolysis ofNaCl or KCl brines. Nitrogen trichlor-ide may also be present in the chlorine

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produced by electrolysis of HCl aqu-eous solutions but is absent from thechlorine produced by electrolysis ofmolten NaCl due to the high tempera-ture conditions in this particular pro-cess.

NCl3 compound was first obtainedby Pierre Louis Dulong (1785–1838)by chlorination of ammonium chloridesolutions. Dulong was seriouslyinjured by several explosions of liquidNCl3.5

NCl3 is liquid under normal tem-perature and pressure conditions.The theoretical atmospheric boilingpoint is 71 8C. The density of the liquidis of 1.635 g/cm3 at ambient tempera-ture, so the liquid may accumulateundetected under water. The pungentodour of NCl3 is that of dirty chlori-nated swimming pools. The vapourpressure of the pure liquid is150 mmHg @ 20 8C and 80 mmHg @0 8C. Due to its high vapour pressureunder ambient temperature, the liquidtends to evaporate quickly. NCl3 istoxic. The recommended occupationalexposure limit in France is of 0.1 ppmand the TLV-STEL is of 0.3 ppm.Occupational exposure can occur inindoor swimming pool areas and incleaning operations using bleach.

The heat of decomposition wasdetermined in carbon tetrachloridesolutions: DH = �54.7 kcal/mol orDH = �457 kcal/kg NCl3. In thisdecomposition, 1 mol of nitrogen and3 mol of chlorine are produced per2 mol of NCl3. The solvent is left unaf-fected in this decomposition.

Liquid NCl3 can detonate in thecondensed phase. The constantvolume detonation of the liquidproduces a maximum pressure of5,500 bar and a maximum temperatureof 2,128 8C.

NCl3 vapour is also unstable and mayexplode above 93 8C or under the influ-ence of light. The limits of the gas phaseexplosive decomposition range in a Pversus T diagram are as follows:

Upper limit: 40 mmHg at 20 8C,70 mmHg at 40 8C, 115 mmHg at 60 8C.Lower limit: 10�3 mmHg at roomtemperature.

The lower explosive limit is difficultto distinguish from the slow reaction.

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Between the lower limit and theupper limit, the decomposition isexplosive and presents a flame propa-gation phenomenon. In the dark, NCl3decomposition flame has a pink colourat low concentration. Above the upperlimit NCl3 vapour decomposes follow-ing a slow reaction mode. NCl3 isthought to detonate also in the gasphase but the study of this detonationin shock tubes is difficult due to theproblem of obtaining a high vapourconcentration.

The very low LEL of NCl3 makespossible the initiation of gas phaseexplosion of flammable chlorine + fuelmixtures by NCl3 vapour at trace con-centration.

Nitrogen trichloride is miscible withliquid chlorine even at chlorine atmo-spheric boiling point of�35 8C. NCl3 isalso soluble in carbon tetrachlorideand chloroform. Other solvents aresometimes mentioned like benzene,ether, carbon disulfide but one shouldavoid solvents which may be chlori-nated by NCl3 or chlorine because thesolution obtained may be unstable andreact violently. NCl3 is a chlorinatingreactant. Solutions of 12–15 wt.%NCl3 in carbon tetrachloride orchloroform are expected to be stableunder ambient temperature but woulddecompose above 60 8C.

The decomposition exothermobtained in DTA under temperaturescan conditions, is influenced by thetest cell wall material. The decomposi-tion pattern shows a chemical accel-eration phenomenon in titanium orstainless steel closed cell, and a slowdecomposition exotherm in closedglass ampoule. In other words, thedecomposition of liquid NCl3 presentsan autocatalytic behaviour and is cat-alyzed by metals like carbon steel,stainless steel and titanium. This parti-cular behaviour finds some industrialapplication in NCl3 thermal destruc-tion processes used in chlorine pro-duction.

Case Histories Concerning NitrogenTrichloride in Chlorine PurificationProcesses

A long time ago, the liquid chlorineused to wash nitrogen trichloride fromgaseous chlorine in the bubble-cap traycolumn described above, was collected

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in one tonne cylinders for use in theBalard reaction, to produce bromineby chlorination of brine containingsodium bromide. An operator felt thata one tonne cylinder was self-heatingabove ambient temperature. The cylin-der did not rupture but it was clear thatthe NCl3 concentration in this residualchlorine was not well controlled andthat this method of NCl3 disposal wasnot safe.

Further to this incident, the processwas modified and carbon tetrachloridewas added to the chlorine purificationcolumn re-boiler to allow NCl3 extrac-tion. The NCl3 solution in liquid chlor-ine was continuously discharged fromthe column bottom to the re-boiler,degassed and the NCl3 in CCl4 solutioncontinuously decomposed in a carbonsteel vessel by raising the solutiontemperature to 45–60 8C. No seriousincident occurred with this type ofdestruction process.

In another example, NCl3 wasextracted by adding a mixture of car-bon tetrachloride and chloroform tothe purification column re-boiler.The NCl3 in liquid chlorine solutionwas admitted to the re-boiler, degassedand withdrawn batch-wise to be sentto incineration. No serious incidentoccurred with this type of destructionprocess.

However, the control of NCl3 con-centration in the CCl4, chloroform andchlorinated organics solution is criticalsince NCl3 maydecompose violently onheating. A runaway reaction accident isdescribed on this process in a pamphletby the American Chlorine Institute.6A

Anoff-linere-boilerusedtodegaschlor-ine fromaNCl3 inCCl4, chloroformandchlorinated organics solution beforeits disposal, exploded on October 17,1967 in a PPG facility at Lake Charles,Louisiana. The NCl3 concentration wasdeduced from the concentration in thecolumn bottom after the incident, to beonly of 8.5 wt.% NCl3. This solutioncould self-heat above the ambient tem-perature of 22 8C and the decomposi-tion could runaway causing the re-boiler vessel rupture underanestimatedpressure of 51 bar and temperature of100 8C.

Another accident case history on thesame type of installation at an unspe-cified location was also reported in a

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letter of February 3, 1995 issued by theChlorine Institute.6B

In this accident, a double block ballvalve system was installed on the liquidchlorine line between the washing col-umn bottom and the re-boiler, becausethe previously installed single ballvalve did not close properly. As theplant was shut down for maintenance,shortly after the process modification,the pipe between the two ball valvesand the ball valves themselves weredestroyed by an explosion, causing achlorine release which killed twooperators.

The column drain pipe flange wasthen sealed using a blind flange and itwas a decided to pump a drum ofcarbon tetrachloride in the washingcolumn bottom. While this was imple-mented a second explosion occurredin the concrete trench below thewashing column where the NCl3 inliquid chlorine solution from the col-umn bottom had been collected. Thissecond explosion severely injured oneoperator. As the NCl3 concentrationwas kept low in this plant column re-boiler, a fast increase of the NCl3concentration in the crude chlorinewas suspected due to an unexpectedcontamination of the salt, brine orchlorine itself. A possible source ofcontamination was ammonia presentin the cooling water used in directcontact with gaseous chlorine fromthe electrolysis room. Also, the deci-sion to install a double block valvesystem and ball valves on the drainpipe from the washing column bottomto the re-boiler was wrong since aNCl3 decomposition could have beenanticipated in this closed pipe and inthe ball valve bodies. The name givento the equipment may be misleading.Of course the washing column maywash also chlorinated organics fromgaseous chlorine and it is also a pre-cooler for gaseous chlorine beforecompression. However, it is impor-tant to state that this equipment isalso designed to collect nitrogen tri-chloride, a very unstable detonatingcompound. Also the column re-boileris designed to evaporate chlorine fromthe carbon tetrachloride solution, butit is also a purge tank or a buffer tankbefore the solution disposal if it is keptat low (0 to 5 8C) temperature or a

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chemical reactor to decompose NCl3if it is operated at high (45 to 60 8C)temperature.

Recommended NCl3 ConcentrationLimits in Commercial Chlorine

Trace concentration of NCl3 is alsopresent in bulk liquid chlorine shippedto customers. Following Eurochlorrecommendations, the NCl3 concen-tration should not exceed 20 ppm in1,000 kg chlorine cylinders, 10 ppm in20,000 and 50,000 kg rail tanks and2 ppm above 300,000 kg chlorineinventory.7

The withdrawal of chlorine from thegaseous phase is forbidden for contain-ers of 1,000 kg and more to avoid con-centrating NCl3 in the vessel.

The accumulation of NCl3 in chlor-ine vaporizers operating continuouslyis possible if the operating temperatureis too low. If the vaporizer operatingtemperature allows enough NCl3decomposition, accumulation doesnot occur.

The recommended frequency ofNCl3 control in chlorine productionis given by Eurochlor depending onthe observed concentration.7

Case Histories Concerning NitrogenTrichloride in Waste Treatments UsingChlorine or Bleach

At least one accident is known whereliquid NCl3 could separate in a waste-water treatment where bleach wasused to oxidize cyanide ions. After anagitation failure, the actuation of abottom valve triggered the detonation.NCl3 was suspected to have collectedin a dense layer in the vessel bottom.Direct chlorination would lead to thesame dangerous situation. It was men-tioned that the pH was not well con-trolled and became too acidic despitethe fact that bleach was used. Thiswould be even easier if direct chlorina-tion had been used. One should takecare that NCl3 may be obtained inwaste-water treatments using chlorineor bleach as an oxidizer if the watercontains ammonium ions, cyanides,amines, amides, urea, ammonia orany ‘‘dangerous’’ nitrogen containingcompound.

In another incident, the cyanidecontaining sludge produced by a cal-cium carbide oven was submitted to

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chlorine injection to reduce their cya-nide content. As the operators wereweeping very much, it was determinedthat cyanogen chloride, ClCN, wasevolving from the liquid. The forma-tion of cyanogen chloride is possible byreaction of chlorine with inorganiccyanides under acidic conditions. Itwas decided to replace chlorine injec-tion by the use of bleach to prevent thisunwanted gas evolution. This sad storyshows that oxidizing conditions arenot always obtained and that othervolatile intermediates may also beformed.

Bromination processes and the pro-cessing of bromine containing reac-tants produce waste solutionscontaining inorganic or organic bro-mides. The incineration of these wasteswould produce bromine which cannotbe released as is in the atmosphere.Some organic bromine product produ-cers offer the reprocessing of thesewastes to recover bromine using theBalard reaction. The bromide contain-ing waste is chlorinated in a glasspacked column where chlorine isinjected in the column bottom andbromine is evolving in the columnupper part where the liquid waste isfed, as usual to carry out the Balardreaction. In this process, a very lowlevel of contamination of the wasteby dangerous nitrogen containingcompounds is safety critical, eitherfor the organic and inorganic compo-nents. In particular, the presence ofammonium ions may cause explosionsdue to the formation of nitrogen tri-chloride in the glass column.

Accumulation of Unstable ChlorinatedCompounds in The Bulk Liquid Phase

The accumulation of unstable chlori-nated products in the bulk liquid phaseis most likely when a solvent is usedwhere this product is soluble. The mostcommon example is nevertheless theaccumulation of NCl3 produced byelectrolysis of KCl or NaCl salt con-taining ammonium ions, in a NCl3removal process using extraction incarbon tetrachloride. If NCl3 is notcontinuously thermally decomposed,high NCl3 concentrations in the CCl4solution are obtained with a potentialrunaway decomposition hazard asdescribed above.

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Miscellaneous Examples

Example of unstable compoundobtained by chlorination of oximes inaqueous solution

The chlorination of organic com-pounds with a N–O bound will leavethis chemical bound unaffected. Forexample the chlorination of organicnitro-compounds does not affect thenitro groups. The chlorination of oxi-mes gives chloro-oximes or chloro-nitroso compounds8,9 which candemix from aqueous solutions givingan unstable dense oil. For example, thechlorination of acetaldoxime gives thewater soluble chloro-acetaldoximewhich isomerises to chloro-nitro-soethane, both unstable compounds.The latter gives an unstable dimer, ablue oil, which demix from aqueoussolutions. This blue oil may decomposeviolently.

This is another example of thedemixion of an unstable chlorinatedcompound from aqueous solutions.This ends in process situations similarto NCl3 formation and demixion.

Example of unstable solid obtained bychlorination reaction

N-bromosuccinimide is a very com-mon brominating reactant. But whatabout N-chlorosuccinimide? This pro-duct can be obtained by radical orphotochemical chlorination of succi-nimide in aqueous solution. After crys-tallization, the wet solid is recoveredbut it must be handled with care. Thesolid explodes on contact with iron.The use of a plastic shovel is recom-mended to handle it.

Recommendations

When chlorine is reacted with organicreactants, especially if nitrogen con-taining compounds or ammonium ionsare present, the possible formationof unstable chlorinated compoundsshould be considered. Any segregationof a separate phase from the bulk liquidis potentially dangerous and should beinvestigatedcarefully.Theseparationofan unstable liquid phase may induce ahigh vapour pressure of the unstableproduct in the gas phase because thegas phase is in equilibrium with theseparated unstable liquid. Thisproblemshould be considered. If no segregation

Chemical Health & Safety, January/Februar

occurs, the process situation is safer,however it is necessary to check forlow concentration of unstable chlori-nated compounds (NCl3, alcohol hypo-chlorites, others, etc.) in the bulk liquidphase.

GAS PHASE EXPLOSION HAZARDS

Gas Phase Explosion Hazards inChlorine Production

In chlorine production by electrolysisof NaCl or KCl brine or HCl solutions,chlorine is obtained in the anodic com-partment and hydrogen is obtained inthe cathode compartment of the elec-trolysis cell. In the mercury cell pro-cess, hydrogen is evolved in theamalgam decomposer, allowing a bet-ter separation between chlorine andhydrogen. In the diaphragm or mem-brane cell process the partial mixing ofthe two gases is more straightforwardand the quality of the two gas separa-tion relies on the pressure equilibriumbetween the cathode and anode com-partments and on the tightness of thecell assembly.

As hydrogen is flammable in chlor-ine, explosions may occur if the com-position of the two gases enters theflammable range of H2 + Cl2 mixtures.The lower flammability limit of hydro-gen in chlorine is: 3.5 vol.% H2. Abovethis limit, the mixture is flammable andmay give violent explosions in vessels.

The upper flammability limit ofhydrogen in chlorine is: 89 vol.%hydrogen. Up to this concentration,the mixture of hydrogen and chlorineis flammable. These limits concern thecombustion and deflagration of the gasmixture.

The mixtures of hydrogen and chlor-ine are known to detonate. The lowerlimit for the detonation of hydrogen inchlorine is: 17.5 vol.% H2, the upperlimit of the detonation range is:83 vol.% hydrogen.

Many severe explosions of H2 + Cl2mixtures occurred in the history of theelectrolysis process due to process fail-ure or incorrect operation. The gasphase explosion hazard makes thetotal liquefaction of chlorine a difficultprocess since the hydrogen concentra-tion in the residual chlorine may riseabove the lower flammability limit of

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hydrogen in chlorine, allowing gas-phase explosion to occur. In case ofthe gas-phase ignition in residualchlorine containing H2, the combus-tion heat can initiate the combustion ofcarbon steel in chlorine, causing achlorine release to the atmosphere.Therefore, total liquefaction is avoidedby sending residual chlorine to ableach production unit or to an on-siteconsumer unit.

The hydrogen produced by electro-lysis processes must be washed withcaustic soda and dried before use inburners or in other processes. Whenhydrogen with trace concentration ofchlorine is released to the atmosphere,spontaneous ignition of the stack exitmay occur, especially by sunnyweather.

The corrosion of carbon steel con-tainers by wet chlorine may produceenough hydrogen to allow the hydrogenconcentration in the container to riseabove the LFL in chlorine, making agas-phase explosion possible. Thehydrogen is produced by the reactionof carbon steel with hydrochloric acidformed by hydrolysis of chlorine givinghydrochloric acid and hypochlorousacid. For this reason, it is important tokeep the water concentration in chlor-ine below the recommended limit.

Gas Phase Explosion Hazards inChlorination Reactions

Continuous or loop gas phase reactors

Gas phase explosion hazard is presentwhen chlorine is mixed with a fuel inthe gas phase. The fuel may be hydro-gen, a solvent or organic vapour,ammonia, etc.

When chlorine is reacted with a fuelin a burner, as in the manufacture ofHCl from hydrogen and chlorine mostincidents occur when the burner is seton-stream, either by lighting the burnerwith a pilot flame or by preheating thegas and the burner. Of course the gasmixture is in the flammable range andexplosions occur due to mal-opera-tion.

Loop reactors are used to reactchlorine with organic reactants in thegas phase. The substrate may be hydro-carbons or mixtures of hydrocarbonswith chlorinated hydrocarbons. In thistype of process, chlorine is the control-

11

Figure 1. 20 L sphere for gas explosion experiments, open.

ling reactant and the reaction iscontrolled by the chlorine to substratemole ratio to obtain the desiredproduct. Under normal operatingconditions, the reaction mixture isnot flammable, the fuel (substrate)concentration is above the upperflammability limit. On reactor start-up, the reactor is preheated to a tem-perature above the auto-ignition tem-perature, where the slow reactionof chlorine with the substrate is active.The substrate vapour is circulatedin the loop and then chlorine is fedto the loop reactor. The reactionof chlorine must be initiated immedi-ately. As the chlorination reactionis exothermic, cooling is providedin the loop to control the temperature.Problems may arise if the chlorina-tion reaction does not start immedi-ately. The chlorine concentrationwill increase in the loop, the gas phasecomposition will enter the flammablerange and on reaction initiation, thereactor will explode. Of course, inter-locks are necessary to interrupt thechlorine inlet flow and provide blan-keting to the gas phase if the reactionexotherm is not detected immediatelyon chlorine injection.

Continuous gas phase reactors areused for the chlorination of butadieneto obtain dichlorobutenes, intermedi-ates in the production of chloroprene.The start-up procedure is similar tothat of gas phase loop reactors andalso the process conditions above theupper flammable limit of butadiene atthe process temperature. A good con-trol of the start-up conditions is alsonecessary.

When chlorine is reacted with a fuelon a catalyst bed, incorrect operationwill result in catalyst burn-out or gasphase explosion before or after thecatalyst. Here the determination ofthe fuel gas flammable limits in chlor-ine are of interest if the feed gas is notin the flammable range in normal pro-cess conditions.

Semi-batch or continuous gas/liquidreactors

When chlorine is injected or bubbledin a liquid phase containing a reactantand/or a solvent in a stirred reactor,chlorine evolution in the reactor gasphase may produce a flammable mix-

12

ture with the reactant, product, solventor reaction mixture vapour. Here blan-keting is difficult as in other oxidationprocesses because the oxidizer isbubbled through the liquid reactionmixture.

As far as possible, it is recommendedto keep the reactor gas phase composi-tion outside the flammable range. Var-ious methods are used:

Chemical H

(1) L

ealt

owering the fuel vapour pressurebelow the Lower FlammabilityLimit in chlorine by lowering theprocess temperature.

(2) R

aising the fuel vapour pressureabove the Upper FlammabilityLimit in chlorine by raising theprocess temperature.

(3) B

lanketing the gas phase by flush-ing the reactor gas phase with an

h & Safety, January/February 2005

Che

inert gas such as nitrogen, CO2,HCl.

Figure 2. 20 L sphere for gas explosion experiments, closed.

To keep the reactor gas phase belowthe LFL in chlorine (method 1) is thesafer method where only proper tem-perature control is necessary.

To keep the reactor gas phase abovethe UFL in chlorine (method 2) maynot be quite safe. On start-up the tem-perature must be set to the processnormal value ensuring enough fuelvapour pressure before chlorine injec-tion. If a condenser is used where thefuel vapour pressure is depleted, thegas flow composition may enter theflammable range. Glass condensersare better not used or protected fromlight.

Blanketing (method 3) is a difficulttechnique when the chlorine flow evol-ving from the liquid reaction mixturemay change as the reaction goes tocompletion.

If chlorine does not evolve in the gasphase in normal process conditions, aninert gas flush in the reactor gas phaseis recommended (see below). If achlorine flow evolves from the liquidreaction mixture unreacted, enoughinert gas flush must be provided inthe reactor gas phase to lower thechlorine concentration below theminimum oxidizer concentration(MOC) of the fuel flammable range.

If HCl is released in the gas phase,this gas contributes to the reactor gasphase blanketing. However, oneshould take into account rapidchanges in the process conditions, ifthe wanted chlorination reaction stopsdue to catalyst depletion or reactantconsumption. More unreacted chlor-ine can be released in the gas phase, theHCl production can disappear. There-fore, monitoring of the gas phase chlor-ine concentration using a chlorineanalyzer is recommended.

Self-ignition, Deflagration andDetonation in the Gas Phase

Self-ignitions of gaseous mixtures con-taining chlorine and a fuel, near theambient temperature, are known. Self-ignitions can turn into severe deflagra-tions or detonations.

Self-ignition occurs in mixtures witha composition both in the flammablerange and outside the previously deter-

mical Health & Safety, January/Februar

mined flammable range. This phenom-enon can be explained as follows:

- T

y

he self-ignition temperature of gas-eous mixtures is not a clear-cut limit.It is best represented by an inductionperiod versus temperature relation.Self-ignition will be observed atlower temperature if a longer induc-tion period is allowed.

- N

ear the self-ignition temperature,the flammable area is enlarged to awide range of equivalence ratios.

- W

hen long induction periods arenecessary, weak ignition sourcescan initiate the explosion, such aslight, wall effects, tar deposits, cata-lyst deposits on the wall, NCl3decomposition flame.5,10

- T

he slow reaction of chlorine withorganic fuels may modify the gasphase composition allowing it toenter the flammable range.

A combination of these influences may

explain the above mentioned self-igni-tion phenomenon outside the flamma-ble range.

Example of self-ignition of solventvapour in chlorine

In a chlorination process using diox-ane as a solvent, the reactor gas phasewas found to present a self-ignitionphenomenon if chlorine was allowedto evolve in the reactor gas phase. Aftera first ignition, a series of subsequent

2005

self-ignitions were observed as if theignition delay was reduced by the pre-vious ignitions. The reactor wall wasfound to be covered with a soot depositproduced by the combustion of diox-ane in chlorine.

Further to this incident, the self-igni-tion of gas phase mixtures of dioxaneand chlorine was thoroughly investi-gated by F. Battin-Leclerc.11,12 Diox-ane is sometimes mentioned as asolvent for chlorination processes13

whereas self-ignitions of dioxane +chlorine mixtures are easily obtainednear the ambient temperature.

The flammable limits of dioxane +chlorine mixtures were determined ina 4.6 L explosion vessel together withthe explosion overpressures and max-imum rates of pressure rise.13 Theexplosion overpressures obtained areof the same order of magnitude of thatof explosion of gaseous fuel in air buthalf of the expected thermodynamicexplosion overpressures in chlorine.

The gas phase detonation of gaseousmixtures of dioxane and chlorine wassuccessfully investigated in shock tubesby A. Elaissi.14,15 The detonation pro-ceeds in shock tubes leaving behind asoot deposit, with a velocity half of thatexpected from the Chapman-Jouguettheory. This mixture was shown to bevery sensitive to detonation comparedto mixtures of fuel in air or oxygen.

The full investigation of this exampleshows that mixtures of organic fuels

13

Table 1. Flammability Limits of Gaseous Fuels in Chlorine Data of Mal’tseva17,18

Fuel Temperature (8C) LFL (vol.%) UFL (vol.%)

Hydrocarbons

with chlorine can exhibit self-ignitionfollowed by deflagration and detona-tion thus explaining violent explosionsobserved in the past.

CH4 20–22 5.6 63.0C2H6 20–22 4.95 55.4C3H8 20–22 4.30 50.0C4H10 20–22 3.31 49.5C5H12 20–22 2.42 43

AlcoholsCH3OH 70 13.8 73.5C2H5OH 83 5.06 64.1C3H7OH 102 3.03 51.5C4H9OH 120 2.53 48.8C5H11OH 143 1.98 37.6

Carboxylic acidsHCOOH 105 27.62 82.0

EXPERIMENTAL SET-UP TO STUDYEXPLOSION LIMITS, EXPLOSIONCHARACTERISTICS AND SELF-IGNITION OF GASEOUS MIXTURES

A new explosion vessel, a 20 L sphere,was built to investigate gas phaseexplosions with special attention forexperiments using chlorine as an oxi-dizer. See Figures 1 and 2.

This new facility allows the measure-ment of:

CH3COOH 122 15.83 56.0C2H5COOH 145 9.33 50.8

- T C3H7COOH 170 7.81 49.8C4H9COOH 190 5.84 48.8

Chloro-alkanes

1

he flammability limits of gaseousmixtures using various ignitionsources: single spark, fusing wire,chemical ignition sources.

CH Cl 20 10.2 56.0

- T

3

CH2Cl2 50 16.7 52.9CHCl Not combustible

he explosion characteristics, i.e.,explosion overpressure and maxi-mum rate of pressure rise.

3

C H Cl 20 8.98 49.2

- T

2 5

1,2-C2H4Cl2 100 16.4 36.8C2H3Cl3 Not combustibleC3H7Cl 60 6.88 41.8C H Cl 100 9.95 35.0

he laminar burning velocitydeduced from the pressure–time hist-ory of the explosion.16 The pressureis recorded at a rate of 20,000Points/s.

3 6 2

C H Cl Not combustible

- T

3 5 3

C4H9Cl 100 5.42 44.5

NB compositions are in percents by volume. Isomers are not specified. Refer to the originalpapers.

he self-ignition temperature andinduction period of gaseous mix-tures, down to a few minutes. Sam-pling is possible to check for gasphase reaction.

- F

lash points in chlorine.The main features of this explosionvessel are:

- Hastelloy C276 walls to lower wall

Table 2. Flammability Limits of Gaseous Fuels in Chlorine Data Published byDokter19 and Medard20

effects, i.e., to prevent the reaction ofchlorine with fuel before ignition,catalysed by stainless steel.

Fuel Temperature (8C) LFL (vol.%) UFL (vol.%) Reference

- T

H2 3.5 89 19CH4 5.51 63 19CH4 100 3.6 66 19

he vessel is made of two half-spheres connected through a flangeassembly kept tight by clamps.

CH4 200 0.6 19CH3Cl 10.2 63 19C2H6 4.95 58.8 19

H2 8 86 20CH4 20 5.6 70 20CH4 100 3.6 20CH4 200 0.6 20C2H6 6.1 58 20C3H8 5 40 20CH3Cl 10 63 20CH2Cl2 16 53 20

The upper half-sphere is fixed,the lower half-sphere is movable, usinga pneumatic jack, to allow quick open-ing of the vessel for frequent cleaning.Combustion in chlorine produces sootdeposits on the walls, which may pro-mote or prevent ignition of subsequentmixtures. Cleaning after each positivetest is necessary to obtain reliable flam-mable limits in chlorine.

The vessel design pressure is200 bar, thus allowing initial pressure

4

of 10 to 20 bar according to theexpected explosion pressure. The ves-sel temperature can be set betweenambient temperature and 300 8C. Mix-

Chemical H

ing is ensured before ignition using apropeller mixer. Central ignition ismade using spark, hot wire or a pyr-otechnic ignition source.

ealth & Safety, January/February 2005

Table 3. Flammability Limits of Gaseous Fuels in Chlorine

Fuel Temperature (8C) LFL (vol.%) UFL (vol.%) Apparatus

CH3Cl 25 7 65 (C)C3H8 70a 2 60 (S)C3H6Cl2 200b 4.5 (S)(CH3)3COCH3 60 2 33 (C)1,4-Dioxane 80 2.5 41 (C)CH3COOH 120 5 36 (C)Acetone 60 4.5 60 (C)Chloro-benzene 130 7.5 43.5 (S)Toluene 160 3.5 50 (S)2-Chloro-toluene 150 5 45 (C)Chloro-toluene 160 4 (S)Di-chloro-toluene 160 6 (S)Tri-chloro-toluene 160 9 (S)2-Fluoro-toluene 100 4 37 (C)

(C): 4.6 L cylinder; (S): 20 L sphere.a Po = 1.7 atmosphere abs.b Po = 1.3 atmosphere abs.

REVIEW OF FLAMMABILITY DATAOF GASEOUS MIXTURESCONTAINING CHLORINE

Flammability Limits

A review of flammability limits of gas-eous mixtures containing chlorine wasfirst given by Mal’tseva, Roslovskii andFrolov.17,18 The experimental set-upused to obtain these data was a dou-ble-wall vertical glass cylinder, 80 mmin diameter and 120 mm high. Theexperiment initial temperature was setby thermostating the vessel. The fuel

Table 4. Auto-ignition Temperature of Gas

Fuel AIT in

CH4

C2H6

Dimethyl etherC1–C3 carboxylic acidsC4–C7 carboxylic acidsC2–C4 carboxylic anhydridesC3–C5 ketonesC1–C8 alcoholsC2–C7 aldehydesH2

CH3ClCH2Cl2C2H6

C3H6

1,2-C3H6Cl2Dioxane (0.26 ATA)Chloro-benzeneC3H8 (1.7 ATA)C3H6 (1.7 ATA)

Chemical Health & Safety, January/Februar

was introduced after evacuation, andallowed to vaporize. Then chlorinewas admitted in the explosion vessel.Mixing was only by molecular diffusion(no stirring). A 10 min waiting time wasobserved before ignition by a spark.

Our comment on this method is thatthe wall material is correct, mixing ispoor or not effective and the waitingtime before ignition is too long andmay have allowed the mixture to reactbefore ignition. The results are sum-marized in Table 1 for the reader con-venience.

eous Fuels in Chlorine

Chlorine (8C) Author

318 18280 18Ambient 18300–320 18230–190 18290–215 18325–205 18225–210 18110–160 18207 19215 19262 19205 19150–100 19180 19100 10,11>165 20 L sphere165 20 L sphere60 20 L sphere

y 2005

Dokter19 and Medard20 publishedsome more data collected in Table 2,together with interesting discussions.

Further flammability data obtainedeither using our 4.6 L stainless steelcylinder described in Ref. 13 (C) orour 20 L Hastelloy C sphere (S) aregiven in Table 3.

Miscellaneous data can be found inthe literature, like the flammability lim-its of benzene in chlorine:21 LFL = 8vol.%, UFL = 52 vol%.

The experimental data is given underatmospheric initial pressure, unlessotherwise specified.

Self-ignition Temperatures

Data on self-ignition temperature ofgaseous mixtures of fuel and chlorineare given by Mal’tseva,18 Dokter19 andothers. A collection of data is given inTable 4.

CONCLUSION

Owing to the importance of chemicalreactions involving free chlorine in thechemical industry, the collection ofexperiences and experimental data isof great interest. This should contri-bute more to process safety than infor-mation on less dangerous chemicals orprocesses. It is surprising that onlylimited effort or support is devoted tocollect safety data on chlorinationreactions. The literature on the safetyof chlorination reactions is very lim-ited compared to the literature on oxi-dation reactions using oxygen. Theauthor hopes that this contributionwill promote further experimentalwork in this field. The new 20 L explo-sion vessel, specially designed to studythe flammability of gaseous mixturescontaining chlorine as an oxidizer willallow the determination of reliabledata at a reasonable cost, for a widerange of initial conditions.

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of aliphatic ketones in methanol. J. Org.Chem. 1981, 46, 2532–2538.

2. Sandmeyer, T. Uber aethyl and methyl-hypochlorit. Berichte D. Chem. Ge-sellschaft, 1886, Jahrg. XIX, 857–861.

3. Sandmeyer, T. Uber den Aethylesterder unterchlorigen Saure. Berichte D.

15

Chem. Gesellschaft, 1885, Jahrg. XVIII,1767–1769.

4. Fort, Roland; Denivelle, Leon Recher-ches sur les hypochlorites d’alcoyle.C.R. Acad. Sci. 1954, 234, 1109–1115.

5. Baillou, Francoise. Proprietes explo-sives du Trichlorure d’Azote gazeux.Thesis dissertation, Universite d’Or-leans, France, 27 September 1990.

6. (A). Nitrogen Trichloride, A Collectionof Reports and Papers. The Chlor-ine Institute, Report, no. 21, Ed. 2;New York, 1975;

(B). Chlorine Precooler Drain PipingExplosion, Report of February 3,1995. The Chlorine Institute; LStreet, N.W. Washington, DC20036, 2001.

7. Maximum Level of Nitrogen Tri-chlor-ide in Liquid Chlorine, DocumentGEST 76/55, 9th ed.; Eurochlor, Brus-sels, September 1990.

8. Piloty,; Steinbock, Berichte, 1902, 35,3113.

9. Steinkopf, W.; Mieg, W.; Herold, J.Berichte, 1920, 53, 1148.

10. Baillou, F.; Lisbet, R.; Dupre, G.;Paillard, C.; Gustin, J. L. Gas phase

16

explosion of nitrogen trichloride: Ap-plication to the safety of chlorineplants and chlorination processes. 7thInternational Symposium on Loss Pre-vention and Safety Promotion in theProcess Industries. Taormina, Italy,May, 1992, (Paper no. 106).

11. Battin-Leclerc, F. Reaction du 1,4-Dioxanne Gazeux en Presence D’oxy-gene ou de Chlore. Thesis dissertation,INPL-ENSIC, Nancy, France, 15 Jan-uary 1991.

12. Battin-Leclerc, F.; Marquaire, P. M.;Come, G. M.; Baronnet, F.; Gustin, J.L. Auto-ignition of gas phase mixturesof 1,4-dioxane and chlorine. 7th Inter-national Symposium on Loss Preven-tion and Safety Promotion in theProcess Industries. Taormina, Italy,May, 1992, (Paper no. 82).

13. Gustin, J. L. Gas-phase explosions ofmixtures of organic compounds withchlorine. 6th International SymposiumLoss Prevention and Safety Promotionin the Process Industries. Oslo, Nor-way, June 19–22, 1989, (Paper no. 91).

14. Elaissi, Abdelkrim. Proprietes Explo-sives des Melanges 1,4-Dioxanne +

Chemical H

Chlore en Phase Vapeur. Thesis dis-sertation, University of Orleans,France, 14 March 1994.

15. Elaissi, A., Dupre, G., Paillard, C.Paper Presented at the 8th Interna-tional Symposium Loss Prevention andSafety Promotion in the Process In-dustries, Antwerpen, 1995.

16. Bradley, D.; Mitcheson, A. Mathema-tical solutions for explosions in sphe-rical vessels. Combust. Flame, 1976,26, 201–217.

17. Mal’tseva, A. S.; Sushchinskiy, V. L.Sov. Chem. Ind. 1971, January, 23–25.

18. Mal’tseva, A. S.; Rozlovskii, A. T.;Zhurnal Vses. khim. Ob-va im. Men-deleeva, 1974, 19(5), 522–551.

19. Dokter, T. Fire and explosion hazardsof chlorine-containing systems. J. Ha-zard. Mater. 1985, 10, 73–87.

20. Medard, L. Les explosifs occasionnels,vol. 1 Lavoisier ed.; Paris, 1987, (pp.172–173).

21. Calingaert, G.; Burt, W. IEC, 1951,43(10), 1341.

ealth & Safety, January/February 2005