Loss Prevention in Heavy Industry Risk Assessment of Large

8/18/2019 Loss Prevention in Heavy Industry Risk Assessment of Large

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these installations is not known. That is why the fol-lowing approach to risk assessment was chosen. Fromthe methods available and recognised in the CzechRepublic, indexing and screening methods (SelectionMethod from Purple Book CPR 18E, IAEA-TEC-DOC-727 method, method based on the Dow’s Fireand Explosion Index) were chosen first of all with theaim to obtain preliminary results of risk assessment,and thus to make a decision on applications of otherdetailed methods. After that the HAZOP method wasemployed and the fault and event trees were used forthe estimation of accident probability. Results of appli-cation of these methods led to the determination of risk acceptability according to the procedure recom-mended by Purple Book CPR 18E methodology.

2. Description of gasholders

The agglomeration of industries in the city of Ostrava is historically connected with heavy indus-tries. The original enterprise was established as earlyas 1828; at present two large metallurgical and engin-eering complexes employing about 8000 and 10,000persons exist there. Furthermore, two coking plants,each operating a large gasholder for storing cokinggas, were included in the assessment. The principalactivity of the above-mentioned metallurgical com-plexes is the production of pig iron and steel. Con-verter steel plants are linked to continuous castingplants for slab and bloom casting; partially, steel is

also cast into ingots. Other centres produce heavyplates and profiles and are tied to related engineeringplants.

In the area under evaluation, the following low-pressure gasholders for storing combustion gases are inoperation:

. four waterless gasholders for storing coking gas(3 150; 000, 1 120; 000m3);

. one waterless gasholder for storing blast-furnace gas(150,000 m3);

. one water-sealed gasholder for storing converter gas(30,000 m3).

A brief technical description of the gasholders is pre-sented for two representatives of the above-mentionedgasholders—one waterless and one water-sealed. Thewaterless gasholder of MAN construction (Maschi-nenfabrik Augsburg Nürnberg, German company) hav-ing a capacity of 150,000 m3 was designed for thestorage of pure coking gas and the compensation of differences between coking gas production and con-sumer consumption. The gasholder MAN is a 24-sidedpolyhedron of diameter 53.6 m and a height of 84 m.The edge length is 7 m. The holder bottom is put on

the concrete bed. Inside the holder, a piston sealed withsealing strips, cloth and oil and closing the gas spaceslides up and down. When filling the gasholder, the pis-ton moves upwards and when emptying, it movesdownwards. The total piston weight is 728,805 kg. Theaverage gas pressure in the gasholder is 3.14 kPa; the

converted maximum gas amount is about 80 t.For converter gas storage, the water-sealed low-press-ure holder of volume of about 30,000 m3 is used. It has acylindrical shape (diameter 50 m, height 35 m) and itslower part is formed by a water-filled tank with a steelbottom. Space required for gas is made by a belt thatforms the upper part of the holder. In the course of gassupplying via the inlet pipeline DN 1600, the belt rises,in the course of gas consumption via the holder pipelineDN 1200, the belt drops. The operation overpressure of gas is 2.5 kPa; the converted maximum amount of gas isapproximately 35 t (Bernatik, Babinec, & Ivanek, 2002).

A view of representative gasholders in the area of thecity of Ostrava is given in Fig. 1.The main hazardous components of these combus-

tion gases are carbon monoxide (CO), hydrogen (H2)and methane (CH4). With reference to a possible extentof consequences of potential accidents, the most haz-

ardous component is toxic CO forming about 8%, 25%and up to 60% of coking gas, blast-furnace gas andconverter gas, respectively.

3. Description of safety measures

In Figs. 2 and 3, the principle of gas storage in thewaterless and the water-sealed gasholder is explainedbriefly (Novak, 1998).

As for the gasholders, many safety measures havebeen adopted to diminish the risks. For example, for

Fig. 1. View of the water-sealed gasholder and a waterless gasholder(behind).

272 A. Bernatik, M. Libisova / Journal of Loss Prevention in the Process Industries 17 (2004) 271–278


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4.2. Screening and indexing methods

For risk assessment, the IAEA-TECDOC-727method (IAEA, 1996), which is widely used in theCzech Republic, and the well-known Dow’s Fire andExplosion Index method (Manual F&EI, 1994) were

also employed. The subsidiary goal of the applicationof these methods was potential comparison with resultsobtained by the selection method.

IAEA-TECDOC-727 published by the InternationalAtomic Energy Agency in the year 1996 is presentedbriefly. The great advantage of the method is a simpleassessment of consequences and the frequency of potential acccidents, which enables the determinationof societal risks. The method makes it possible to clas-sify hazards of fixed sources, mobile sources and pro-duct pipelines. It is based on a model of 46 type‘‘reference’’ industrial accidents, when a risk to the

population is the relation of the number of fatalities tothe frequency of events. Results are usually presentedgraphically in the (x, y) coordinate system, where clas-ses of consequences and classes of probabilities (riskmatrices) are plotted along the x and y axes, respect-ively. The existing experience shows that this methodmay be used in the following cases:

– the production of a preliminary general quantitativeoverview of various sources of risk in a larger indus-trial area from the point of view of societal risks,

– the determination of priorities with different sourcesof risk for another detailed analysis.

The outcome is a finding that the IAEA-TECDOC-727 method is applicable to the estimation of neithersocietal risks of gasholders for storing combustiongases, nor their relevant pipeline networks with regardto the pressures of gases in the gasholders and in thenetwork (about 3–5 kPa) and pipeline dimensions (e.g.DN 500). The gasholder as a source of risk can beassigned to none of the 46 ‘‘reference’’ accidents.

The highest value of the fire and explosion index,F&EI ¼ 91:7, classes the gasholder, with which thisvalue was acquired, to the second, moderate hazard

degree for operational units. The radius of the areaaffected may be estimated at 23.3 m (plus the gasholderradius of 27 m). The F&EI study has proved that thegasholders do not represent any significant source of fire and explosion risks.

The calculation of the Dow’s Chemical ExposureIndex (AIChE, 1994) was performed as well; e.g. for thecoking gas holder MAN, the index, CEI ¼ 32:84, and thedangerous distance, HD3 ¼ 274:8 m (for ERPG-3 ¼

500 mg=m3 of carbon monoxide) were determined.Although according to the CEI methodology any otheranalysis is not required if the index is smaller than 200,

these preliminary results show the greater importance of potential accidents in case of a toxic gas cloud release.

4.3. HAZOP method

The carried out HAZOP-studies were concerned withthe identification of non-typical sources of risksaccording to specific conditions of gasholder operation.As the most important causes of potential accidentswere identified, for example, a human factor failure,the influence of climatic conditions, sealing oil quality,failures of measurement and/or signalling trans-mission, and others. More details about these largelyoperational problems that could cause a release of combustion gases are given in Chapter 5.

4.4. Modelling of toxic cloud dispersion

Consequences of releasing a CO toxic cloud were

evaluated in detail; the cloud being able to reach resi-dential areas under unfavourable meteorological con-ditions. For modelling, the ALOHA (Areal Locationsof Hazardous Atmospheres) program prepared by theUS Environmental Protection Agency (US EPA, 1999)was chosen. ALOHA is a computer program designedespecially for use by people responding to chemicalaccidents, as well as for emergency planning and train-ing. ALOHA can predict the rates at which chemicalvapours may escape into the atmosphere from brokengas pipelines, leaking tanks, and evaporating puddles.It can then predict how a hazardous gas cloud mightdisperse in the atmosphere after an accidental chemicalrelease.

By using the ALOHA program, areas affected weredefined according to various scenarios of potentialgasholder accidents. At first, the probit function for theestimation of fatal injuries by carbon monoxide wasused (Purple Book, 1999):

Pr ¼ a þ b ln ðC n tÞ5

¼ 7:4 þ 1 ln ðC 1 30Þ ) C

¼ 8093 mg=m3 ffi 7000 ppm ð1Þ

with Pr the probit corresponding to the probability of fatal injury (–); a, b, n the constants describing the tox-

icity of a substance (–); C the concentration (mg/m3)and t the exposure time (minutes).

The probit makes it possible to determine the con-centration that at the given time produces expectedconsequences. The ALOHA system will then enable thedetermination of the size and the shape of the areaaffected. For the determined LC concentrations (bymeans of the probit), boundaries of the area with thecorresponding probability of fatal injury may be found.

For the purpose of modelling the consequences of population exposure to the effects of toxic substances(societal risk), the LC50 concentration (inhal., 30 min)



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. as it follows from the wind rose, the probability of affecting the dwelling houses is 3.38% (P ¼ 0:0338).

At the independence of both the events (convertergas released from the gasholder and the above-mentioned atmospheric conditions obtained), the

probability of intersection of both the events may bedetermined as an arithmetic product:

5 106 0:0338 ¼ 1:6 107=year

4.6.2. Estimation of the number of fatal injuriesAt a plume length of 157 m, the number of persons

in the area affected was about 30. Furthermore, the cal-culation of the number of factually fatally injured per-sons was executed in accordance with the methodologygiven in Purple Book. It is expected that fractions of population inside the buildings ( f pop, in) and of popu-lation outside the buildings ( f pop, out) may be estimated.

The situation changes within 24 h being different fromday to night. Estimates are given in Table 2.

Moreover, it is assumed that people present inthe area affected by effects of a toxic substance of the above-mentioned concentration occurring outsidethe buildings will be fatally injured with a probabilitygiven by the probit value. Ten percent of people (0.1factor) present inside buildings will be fatally injured.

Results are presented in Tables 3 and 4.

4.6.3. Assessment of societal risk acceptabilityIn accordance with the Czech laws (Act No. 353/

1999, Coll.), the acceptable event occurrence frequencyis determined according to the relation given below:

F p ¼ 103=N2 for an existing establishment or installation

ð2Þ

F p ¼ 104=N2 for a new establishment or installation

ð3Þ

where F p is the acceptable frequency and N the numberof endangered persons.

In our case, it is the frequency with the number of five fatally injured that is acceptable:

F p ¼ 103=52 ¼ 4 105=year

From the comparison of the frequency of eventoccurrence and the acceptable frequency it follows that

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The channel is filled as requested with sealing oil, inwhich the whole runner is submerged. The sealing oillubricates the wall of gasholder shell as well as the runnerand seals thus a gap between the wall and the runner.

. If the sealing strip of the piston is damaged, thesealing oil from the upper channel will fall to thelower channel, and thus the level will drop. If it isnot possible to supply the oil into the upper channel,the gas will rise above the piston;

. The heating of the gasholder by a heating coil—inwinter periods it is necessary to ensure the heatingof the gasholder, especially of the upper channel to

keep the correct viscosity of the sealing oil.. Piston tilting or jamming—problems associated with

the piston may occur due to incorrect loading, orintensive sunshine, or impurities frozen on the wallsof the gasholder; the operating staff must observethe tilt of the piston to prevent the gas from escap-ing around the piston.

Several operational problems occurred in the asses-sed gasholders. Fortunately, none of them led to anymajor accident. Moreover, on the basis of the historicaloverview of accidents in the gas industry all over the

world (Novak, 1998) it is possible to state that con-sidering the number of gasholders operated, the num-ber of major accidents is rather small (e.g. accidents inPittsburgh in the year 1927 and Neunkirchen in theyear 1933).

6. Conclusion

Six large gasholders in the area of one town rep-resent untypical sources of major accident risks. Thegasholders create, thanks to their size, landmarks in the

whole city and constitute, from the point of view of prevention of major accidents in heavy industries, prac-tically the most significant hazard with regard to thechemical composition of coking, converter and blast-furnace gases, when the main dangerous componentsare carbon monoxide, hydrogen and methane.

It follows from comprehensive results of the riskanalysis that the highest risk is connected with a releaseof a large amount of converter gas containing CO (upto 60%), when the population in the close vicinity maybe endangered. With reference to a historical connec-tion between some gasholders and residential areas, thegasholder for storing coking gas (8% of CO) and pipe-lines even several kilometres long were assessed assources of risk as well. Some of the gasholders alsorepresent significant risks of major accidents to sur-rounding public transport. In the nearby area of twogasholders a road with tramlines leads that could be,under specific conditions, a cause of gas cloud

explosion.Furthermore, the risk analysis verified the usability

of some recognised methods for risk assessment. Onthe one hand, the inapplicability of the IAEA-TEC-DOC-727 screening method to the assessment of gasholders was proved in spite of the fact that thismethod has been often employed in the Czech Repub-lic. Modelling the dispersion of a released toxic cloudby means of the ALOHA program also brought pro-blems with regard to specific operational conditions(especially the low overpressure of gas in thegasholder). On the other hand, the Dutch method-

ology, Purple Book, namely both the introductoryselection method and other procedures for the assess-ment of probability and risk acceptability, proved itself to be suitable. The systematic method HAZOPapproved itself as an appropriate method for thedetailed analysis of causes of potential accidents andpossible operational problems.

In the conclusion it is possible to state that with theassessed gasholders, total safety as well as reliability israther high; the reliability and the safety may be con-sidered to be societally acceptable. Nevertheless, withregard to the age of the gasholders, high-quality main-tenance and inspection of the conditions of these instal-lations must be done. Furthermore, it is necessary toassess the reliability of human factor in detail and toevaluate operational problems arisen, which will leadto improvement in major accident prevention with thelarge gasholders.

References

Act No. 353/1999 Coll., on prevention of major accidents andDecree of the Ministry of the Environment No. 8/2000 layingdown the principles of major accident risk assessment.

Fig. 7. Scheme of piston sealing in the gasholder MAN (Novak,1998). Principle of sealing—on the lateral surface there is a peripheralchannel connected by means of cloth to a runner. The runner is pres-sed elastically against the inner smooth wall of the gasholder. Whenthe piston rises and drops the runner slides on the gasholder wall.

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AIChE technical manual Dow’s Chemical Exposure Index (1994).American Institute of Chemical Engineers.

Bernatik, A., Babinec, F., & Ivanek L. (2002). Bezpečnostnı́ zprávaEVi a.s. (Safety Report).

IAEA-TECDOC-727 (1996). Manual for the classification and prior-itisation of risks due to major accidents in process and relatedindustries. Austria: International Atomic Energy Agency.

Manual—Dow’s Fire & Explosion Index (1994). Hazard classification

guide (7th ed.).

Novak R. (1998). Nehody a havárie nı́zkotlakých plynojemů v ply-nárenské historii, (Accidents of low-pressure gasholders in gasindustry history). Energie, 1, 77–82.

Purple Book CPR 18E (1999). Guidelines for quantitative risk assess-ment. The Hague.

US EPA (1999). CAMEO ALOHA, http://www.epa.gov/ceppo/cameo/aloha.htm.


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Loss Prevention in Heavy Industry Risk Assessment of Large