Evaluation model for safety capacity of chemical industrial park based on acceptable regional risk☆

Guohua Chen*,Shukun Wang,Xiaoqun Tan

Institute of Safety Science and Engineering,South China University of Technology,Guangzhou 510641,China

Keywords:SCCIP Safety transport capacity Safety storage capacity Regional risk

ABSTRACT The paper defines the Safety Capacity of Chemical Industrial Park(SCCIP)from the perspective of acceptable regional risk.For the purpose of exploring the evaluation model for the SCCIP,a method based on quantitative risk assessment was adopted for evaluating transport risk and to confirm reasonable safety transport capacity of chemical industrial park,and then by combining with the safety storage capacity,a SCCIP evaluation model was put forward.The SCCIP was decided by the smaller one between the largest safety storage capacity and the maximum safety transport capacity,or else,the regional risk of the park will exceed the acceptable level.The developed method was applied to a chemical industrial park in Guangdong province to obtain the maximum safety transport capacity and the SCCIP.The results can be realized in the regional risk control of the park effectively.

1.Introduction

New approaches for facility distribution in chemical plants were proposed[1],and the influence of vapor cloud shape on temperature field effect of unconfined vapor cloud explosion(UVCE)was analyzed and a creditable prediction method of explosion temperature effect was obtained[2],but the value of qualitative research on SCCIP is not high enough for engineering application up to now[3]and the conclusion of the quantitative research cannot obtain the safety storage capacity of dangerous goods within chemical industrial park accurately.It is also not studied in-depth that the quantitative relationship between all kinds of transportation risks and the traffics of dangerous goods[4],and the total safety transport capacity cannot be expected by using an accurate quantitative risk methodology[5].Most scholars agree that SCCIP is the total load of dangerous goods based on its security which can be guaranteed[6],and the research is based on the acceptable risk of dangerous goods and the safety capacity is the critical volume of acceptable regional risk in the chemical industrial park[7].In the range of acceptable risk,the critical quantity of dangerous goods is determined by the comprehensive risk such as production and storage,transport and so on[8-10].For a simplified calculation of the capacity in the chemical industrial park,other kinds of risks can be mostly avoided by management besides transport.In other words,as long as transport of dangerous goods is security,the total amount of dangerous goods transported into chemical industrial park can be accepted by all enterprises.However,this method neither considers the carrying capacity of the dangerous goods obviously,nor provides safe operation guide for each enterprise in the internal park.For further exploring the connotation and method of SCCIP,the factors of enterprise and transport need to be taken into consideration synthetically,and thus it can provide an effective decision-making about the scale of the dangerous goods for government and enterprises.

2.Definition of SCCIP

The purpose on SCCIP is to control the risk introduced by dangerous goods effectively.The safety capacity in chemical industrial park can be defined as the largest inherent allowable value and the maximum transport allowable value of the acceptable regional risk through combining the nature of the enterprises,comprehensive analysis of the attributes and characteristics of dangerous goods,transport characteristics of the enterprises,and the risk management situation of the park.In other words,SCCIP is the total amount of dangerous goods which is determined by the largest safety storage and maximum safety transport capacity that a chemical industrial park can bear.Where the largest safety storage is the total amount of dangerous goods which enterprises can accommodate within the acceptable risk,the maximum safety transport capacity is the transport amount of dangerous goods within acceptable transport risk at a given time.According to the definition,the relationship among dangerous goods,inherent risk,transport risk and the construct of safety capacity are shown in Fig.1 and has been studied by Wang et al.[11].The paper focuses on the safety of transport,and combining it with the safety storage to construct safety capacity evaluation model in the chemical industrial park.

Fig.1.Flow chart of safety capacity research[11].

3.Evaluations of Safety Transport Capacity in the Chemical Industrial Park

For all kinds of transport of dangerous goods in the chemical industrial park,road transports often accompany with personal and social risks because they usually pass through the concentration areas of population and enterprises.Road safety transport capacity is taken as the breakthrough in the paper.Road transports mainly include highway transport and railway transport.Basically,both of the two kinds of transports are of the same risk assessment principle.Road transport data are relatively integrates and the transport within the chemical industrial park is primary highway transport.Therefore,the road transport is mainly pointed to the highway transport in the paper.The relationship between different kinds of transport risk and the quantitative transport capacity of dangerous goods on the road in the chemical industrial park is researched through basic risk assessment theory.Regarding the allowed standard risk as control factors,the road safety transport capacity of the park can be calculated,and then the safety transport capacity can be obtained.The scheme is shown in Fig.2.According to the accident of dangerous goods on road transport,there are three kinds of dangerous goods typically such as explosive,in flammable and toxic dangerous goods.When constructing safety transport capacity evaluation model,the basic principle is the same and only needs to be adjusted according to the type of specific dangerous goods.

3.1.Road transport risk evaluation model

The data of leakage accident show that the consequence of small leakage is not serious generally.The traffic accident can be only taken into consideration as road transport risk which is caused by a large leakage of transport of dangerous goods.

The road transport risk is based on the idea that the road is divided into several sections denoted as liin section i of road L,whose road accident probability of dangerous goods is mainly lied on the probability of traffic accidents,conditional probability of leakage and the large leakage rate(0.35[12]).It is supposed that each transport accident is independent.Accident probability f(li)of transport of dangerous goods at any point in lican be expressed as follows[13]:

where paci(li)is the number of transport accidents per year(accidents/year)on road liand can be obtained following Erhan and Vedat[14]and Harwood and Viner[15],N is the number of transport vehicles flow on average(number/year)of the road liand Ptis the conditional probability of leakage of dangerous goods caused by traffic accident.

Fig.2.Flow chart of safety transport research.

Due to the probability of transport accident of dangerous goods paciN（li）is usually 10?6-10?8[4](times per kilometer),paciN（li）can be ignored and formula(1)can be simplified as formula(2):

The personal death probability of circumambient points(x,y)caused by road transport accident on section lican be expressed as formula(3)[16,17]:

whereλis the biggest impact distance(km)caused by dangerous goods transport accident,yeis the vertical distance(km)between the calculated point and the centerline of transport routes,ye＜ λ,as shown in Fig.3[18]and L(li)is length(km)of road section li.

Fig.3.Vertical distance between the calculated point and the centerline of transport routes[18].

3.2.Relationship between road transport risk and road transport capacity

According to the analysis above,the risk is caused by dangerous goods transport which consists of accident probability and personal death probability.According to formulas(2)and(3),personal risk at any point caused by transport accident of dangerous goods can be calculated as follows:

According to formula(4),the transport risk is a positive proportion to the number of transport vehicles.If the carrying capacity of transport vehicles is known,the risk corresponding to road transport volume of dangerous goods can be calculated.Currently,the hypothesis that the damage degree is the same if the accident of dangerous goods happened in the same type is taken in the transport vehicle risk assessment model.In fact,for similar types of dangerous goods,the range of accident casualties could not be the same each time.The difference of casualty range mainly comes from the carrying amount of transport vehicles[19].The emergency evacuation distance was regarded as the biggest casualty radius[12],which is expressed in Table 1.The dangerous goods type is obviously considered,but the differences among casualty areas caused by the different volume of dangerous goods are not differentiated.Therefore,the transport risk is revised from the perspective of the equivalent load capacity and the quantitative relationship between transport risks and the safety transport volume is confirmed.

It is supposed that the carrying amount only affects the accident consequences.In order to ensure that the vehicles are independent of each other,the assumptions are made as follows[20]:

Assumption 1.There are enough time intervals between transport vehicles.The accident in each section of the road is independent of each other,and the accident will not interrupt the transportation process.

Assumption 2.When the carrying capacity of each vehicle is different,except the carrying capacity,other factors which affect the accident probability and consequences are taken as the same.

Safety transport capacity consists of the number and load volume of transport vehicles at a given time.Because the types of vehicles for transporting dangerous goods are plentiful and changeable,the concept of equivalent load capacity is introduced.The equivalent of dangerous goods transport and casualties' radius of accident consequences are put forward and defined.The essence of equivalent load capacity is the expectation of transport carrying amount for each type of dangerous goods.

3.2.1.Equivalent load capacity and equivalent casualties' radius of explosive dangerous goods

When road transport risk is calculated,the expectation of the largest load transport is taken as equivalent load capacity of explosive dangerous goods.It can be calculated as follows:

where c1is equivalent load capacity of explosive dangerous goods(t),α1iis the weight about road transport capacity of explosive dangerous goods in the park,w1iis the transport load which is the largest transport load vehicle of type i's explosive dangerous goods(t)and m1is the types of explosive dangerous.

The harmful radius of explosion dangerous goods is usually calculated with TNT equivalent method.It can be shown as formula(6)[21].

where WTNTis the TNT equivalent capacity(kg)of explosion dangerous goods,α is explosive efficiency parameters within 0.02%-14.9%,Wfis the amount(kg)of the explosives in burning gas clouds,Qfis the heat of combustion of explosion and QTNTis the heat of combustion of TNT(MJ·kg?1).

Explosion makes a person harmful through the overpressure shock waves.The relationship between overpressure shock waves Δp and the explosion center distance D can be shown as formula(7)[22]:

When the casualties' overpressure is equal to Δp,D is equal to casualties' radius r.When the same type of different amounts ofdangerous goods blast and all reach to casualties' overpressure,there isin the wave surface,and then,we have:

Table 1 The emergency evacuation distance of different dangerous goods[12]

For similar types of explosive dangerous goods,formula(8)can be simplified as follows:

where Wxand Wyare the different explosive transport capacities,and rxand ryare the maximum radius(km)of casualties' overpressure wave for Wxand Wy.

For all types of explosive dangerous goods,the largest casualties'radius can be calculated withfor vehicles carrying explosive dangerous goods by taking the radius corresponding to the largest TNT equivalent as the emergency evacuation distance.Thus,the equivalent casualties'radius r1of vehicles carrying explosive dangerous goods can be calculated as follows:

where r1iis equivalent radius of explosive dangerous goods i,α1iis the weight of explosive dangerous goods i with same values of formula(5)and m1is the total type of explosive dangerous goods.

3.2.2.Equivalent load capacity and equivalent casualties' radius of flammable and poisonous dangerous goods

For flammable dangerous goods,the expectation of the largest flammable load capacity is taken as equivalent load capacity.It can be calculated as follows:

where c2is equivalent load capacity of flammable dangerous goods(t),α2jis the weight about road transport capacity of flammable dangerous goods in the park with the same value in formula(5),w2jis the transport load which is the largest transport load vehicle of type j's flammable dangerous goods(t)and m2is the total type of flammable dangerous.

The emergency evacuation distance is taken as the maximal potential radius.The ratio between the equivalent load capacity and the maximum load capacity is regarded as the weight of the accident casualty radius.Equivalent casualties' radius r2of flammable dangerous goods can be expressed as follows:

where r2is the revised influence radius(km)based on the transport situation in the chemical industrial park,wmaxis the largest load capacity(t)among each type of vehicles and λ2is the accidental evacuation distance(km)of flammable dangerous goods.

Similarly to flammable dangerous goods,the corresponding equivalent load capacity C3and equivalent casualties'radius r3of poisonous dangerous goods can be calculated.

3.3.Evaluation on road safety transport capacity

3.3.1.The number of vehicles for dangerous goods transport

Safety transport capacity is mainly determined by transport risk,but the precondition is that each vehicle is independent with each other among the transport risk calculation formula(4).Therefore,it should be ensured that the distance between transport vehicles is enough to reach the independent requirement.The influence factors on safety transport capacity include two aspects of the safety distance and the transport risk.

It is hypothesize that the production cycle of the park is set as T and the dangerous goods carried into the chemical industrial park are in 12 h a day.Then,the calculation cycle of road safety transport capacity of dangerous goods is 365×12/T.It can be seen that other vehicles will not affect the accident vehicle after the accident vehicle is evacuated.Therefore,if only the distance among vehicles meet the evacuation time,it will ensure that the vehicles are independent and could not interrupt transport.According to the emergency evacuation time,the evacuated time of the road with single lane is 20 min and multi-lane is 15 min.Then the total number of road transport vehicles can be decided by the departure time of each vehicle and can be expressed as formula(13),

where nt1is the maximum number of vehicles determined by the safety distance,T is production cycle in the chemical industrial park and tevais the evacuated time(h).

3.3.2.Calculation model of road safety transport capacity

Because the safety distance between all kinds of dangerous goods vehicles is based on the evacuated time;thus,the safety distance can be ensured when all kinds of transport vehicles of dangerous goods are driven on the road.Substitute formula(3)into formula(4),we can obtain the risk with only one type of dangerous goods as formula(14):

Three typical types of dangerous goods transport vehicles of a production cycle should meet the individual acceptable risk.It can be expressed as follows:

Then,the road safety transport capacity for the chemical industrial park can be calculated by:

where c1,c2and c3are the equivalent load capacity(t)of explosive,flammable and poisonous dangerous goods.

The maximum safety transport capacity in the chemical industrial park can be calculated as follows:

where β is the ratio between the actual road transport amount of dangerous goods per year and the total transport amount of all chemical goods per year in a chemical industrial park.

4.Safety Capacity Evaluation Model of the Chemical Industrial Park

It could be in danger if the SCCIP exceeds the largest safety storage amount or the maximum safety transport amount.Therefore,SCCIP depends on the smaller one between the largest safety storage and maximum safety transport capacity in the chemical industrial park.According to reference[11],the calculation model of dangerous goods amount stored in chemical industrial park can be obtained.

The safety capacity evaluation model of chemical industrial park can be stated as:

where Cf1maxis the amount of dangerous goods stored in existing enterprises,Cf2maxis the storage amount of dangerous goods that will be brought into the chemical industrial park with new enterprises built or existing enterprise expanded and Cmaxis the maximum amount of safety transport in the chemical industrial park.

5.Engineering Application of SCCIP

The major data observed in a chemical industrial park in Guangdong province are shown in Table 2.The ratio of transport and storage volume per year is recorded as the production cycle in the park.According to the dangerous goods transport data reported by Wang et al.[11],the cycle can be calculated as 11.4.There are many different dangerous goods with poisonous, flammable and corrosive properties in the chemical industrial park.There are three main kinds of dangerous goods to be taken into consideration in estimation of safety transport capacity in the park.

Table 2The largest carrying amount of the main dangerous goods

According to formula(11),the equivalent load capacities of flammable,poisonous and corrosive goods in the park are 36.73,40 and 61.35 t,respectively.Because the limited load of the only bridge which is bound for the park is 25 t,the weight of the transport vehicles is assumed as 5 t,and then the equivalent load capacity is 20 t actually.According to formula(12),with the emergency evacuation distance in Table 1 taken as the largest casualty radius,the calculation of equivalent casualty radius is shown in Table 3.

There are two main roads which are bound for the chemical industrial park and the basic characteristics of the two main roads are consistent.The length of the road is 9 km.Thus,only one main road needs to be calculated and then multiplied by 2.To ensure the safety of the road transport,vehicles should be independent of each other.The departure time between adjacent vehicles should be 0.25 h at least.According to formula(13),the total number of vehicles is determined by the safe distance in a production cycle and can be calculated as:

The risk of accident should meet formula(20).

According to the equivalent load capacity(20 t)and the dangerous goods transport data[9],the ratio of transport vehicles of flammable,poisonous and corrosive dangerous goods is 12.7424:7.3685:12.9974(1.73:1:1.76).According to formula(20),the risk caused by the road transport can be calculated as:

With the equivalent load capacity of 20 t,we have that N2*=962,N3*=556 and N4*=979,and the total number of transport vehicles is 2497,which is less than 3073 determined by the safe distance in a production cycle.

According to formula(16),the largest road safety transport capacity of flammable,poisonous,corrosive dangerous goods in a production cycle in the chemical industrial park is 49940 t(2497×20 t).The transport capacity of general dangerous goods in a production cycle is 17904.82 t(204115 t/11.4)[11].Thus,the maximum road safety transport capacity of general dangerous goods in a production cycle is 17904.82 t×1.72=30796.30 t.The maximum road safety transport capacity is the sum of49940 t and 30796.30 t(80736.3 t).With the consideration of road safe transport contribution rate as 0.8,C*equals to 80736.3 t×0.8(64589.04 t).

According to formula(17),the maximum safety transport capacity which is determined by all transport types in the park can be calculated by:

The maximum safety transport capacity per year is 13892736.91 t(1218661.132 t×11.4).It is shown that safety transport of dangerous goods is in the safe situation.In addition to keeping dangerous goods of 930000 t to each production cycle in the park,the maximum safety transport capacity still have a safety margin of 288700 t.

According to the largest safety storage data provided by Wang et al.[11]and the maximum safety transport capacity of this paper,the data compared with the current situation are shown in Table 4.

Table 4 Contrast between the statistical results and the current situation in the chemical industrial park

Table 3 Equivalent casualty radius of transport dangerous goods accident

According to formula(18)and Table 4,the SCCIP depends on the smaller one between the largest safety storage and the maximum safety transport capacity.Thus,the SCCIP is 1218661.132 t(=Cf1max=Cf2max).

6.Conclusions

(1)The dangerous goods capacity of existing enterprises in this chemical industrial park has not yet reached the saturation.When the industrial structure remains the same,the amount of dangerous goods can be increased continually in both aspects of safety storage amount and safety transport amount.But according to Table 4,the amount of dangerous goods transport which can be added is obviously less than that of dangerous goods storage in this chemical industrial park.It is known that the safety transport is the bottleneck in increasing the safety capacity in this chemical industrial park.

(2)SCCIP is mainly restricted by the transport risk.The main reason is that transport becomes the bottleneck factor of the safety capacity in this park.If a number of dangerous goods inventory of raw materials is increased,transport burden will be increased multiply.The transport burden is the inventory of raw materials multiplied by the production cycle T.

(3)At present,the largest safety storage of chemical industrial park still has a large space.But due to the constraint of transport capacity,the park should pay more attention in improving the transport condition in the future at the same time with the development of the park.Otherwise the safety capacity in this chemical industrial park will not increase with the expansion or construction of enterprises.

Nomenclature

Cf1maxamount of dangerous goods stored in existing enterprises,t

Cf2maxamount of dangerous goods that will be brought into the park with new enterprises built or existing enterprise expanded,t

Cmaxmaximum safety transport capacity,t

C* road safety transport capacity,t

c1equivalent load capacity of explosive dangerous goods,t

c2equivalent load capacity of flammable dangerous goods,t

c3equivalent load capacity of poisonous dangerous goods,t

D explosion center distance,km

f(li) accident probability of dangerous goods transport at any point in li

L(li) length of road section li,km

m1total type of explosive dangerous goods

m2total type of flammable dangerous goods

N number of transport vehicle flow on average of the road

N1*number of transport vehicles with explosive dangerous goods

N2*number of transport vehicles with flammable dangerous goods

N3*number of transport vehicles with poisonous dangerous goods

nt1maximum number of vehicles determined by the safety distance

paci(li) number of transport accidents per year on road li

paciN（li） probability of transport accident of dangerous goods

ptconditional probability of leakage of dangerous goods caused by traffic accident

Δp overpressure shock waves

Qfheat of combustion of explosion,MJ·kg?1

QTNTheat of combustion of TNT,MJ·kg?1

R personal risk

Rupupper limit of individual risk(=10?4)

r casualties' radius,km

r1equivalent casualty radius of explosive dangerous goods,km

r2equivalent casualty radius of flammable dangerous goods,km

r3equivalent casualty radius of poisonous dangerous goods,km

r1iequivalent radius of explosive dangerous goods i,km

T production cycle

tevaevacuation time,h

Wfamount of the explosives in burning gas clouds,kg

WTNTTNT equivalent capacity of explosion dangerous goods,kg

wmaxlargest load capacity among each type of vehicles,t

w1itransport load which is the largest transport load vehicle of type i's explosive dangerous goods,t

w2jtransport load which is the largest transport load vehicle of type j's flammable dangerous goods,t

yevertical distance between the calculated point and the centerline of transport routes,km

α explosive efficiency parameters(=0.02%-14.9%)

α1iweight about road transport capacity of explosive dangerous goods i

α2jweight about road transport capacity of flammable dangerous goods j

β ratio between the actual road transport amount of dangerous goods per year and the total transport amount of all chemical goods per year

λ biggest impact distance caused by dangerous goods transport accident,km

λ2accidental evacuation distance of flammable dangerous goods,km