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Comparative Study on Blast Wave Propagation of Natural Gas Vapor Cloud Explosions (VCEs) in Open Space Based on Full-scale Experiment Kan Wang, Zhen-Yi Liu, Xinming Qian, Mingzhi Li, and Ping Huang Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 24 Jun 2016 Downloaded from http://pubs.acs.org on June 24, 2016

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Comparative Study on Blast Wave Propagation of Natural Gas Vapor Cloud Explosions (VCEs) in Open Space Based on Full-scale Experiment and PHAST Kan Wanga, Zhenyi Liua,*, Xinming Qiana, Mingzhi Lia, Ping Huanga a

State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing, China

* Corresponding author at: School of Mechatronical Engineering, Beijing Institute of Technology, No.5 South Zhongguancun Street, Beijing, China. Tel.: +86 13811929080. E-mail address: [email protected] (Z. Liu).

ABSTRACT This study is related to consequence analyses of accidental natural gas explosions and used to assess the risk of the long distance transmission pipeline system. In these consequence analyses, it’s indispensable to adequately predict the blast wave propagation of gas vapor cloud explosions in open space. In this study, a new theoretical prediction method for natural gas VCEs in open space was developed and a full-scale experiment involving explosion in a natural gas pipeline was carried out. The predictions by improved theoretical method agreed well with the results of full-scale experiment. Based on damage criteria, to demonstrate the probability and potential damage range to humans and surroundings, risk analysis of this case was performed on PHAST simulator, we conclude that, a nearly 100% fatality is expected in a blast wave zone of within 160 m, while the explosions made serious effects on the surrounding constructions with causing all the buildings collapsing with the radial distance of 156 m. Relatively, there is no harm when the people stay beyond the ellipse diameter of 545 m and no damage to the surrounding buildings beyond the radial distance of 1755 m. Keywords: Natural gas explosion, Blast wave propagation, Full-scale experiment, Theroetical prediction, PHAST.

1.

INTRODUCTION With the necessity to focus on the safety development of the natural gas long distance

transmission, it has been long understood that natural gas explosions can generate a blast wave propagation, especially when the gas vapor cloud explosions (VCEs) happen in of open space. As concern has increased about the possible consequences of a natural gas explosion in industrial plants, so accurate predictions of such explosions are needed. Several large scale experimental studies for high pressure natural gas pipelines have been conducted in support of the development of the internationally used pipeline risk assessment for natural gas pipelines1 and two pipeline rupture experiments were performed at full-scale.2 More recently, two pipeline rupture experiments were performed using a similar test rig with a 150 mm diameter pipeline pressurized with natural gas.3 Previous studies of VCEs in open space have shown that more reactive fuels are more susceptible to flame acceleration through the gas pipeline.4-6 On theoretical aspect, VCEs are usually analyzed by means of simplified models, such as the TNT equivalent method and its later developments.7-9 Recently, several models have been proposed to predict the intensity of the blast wave induced by an explosion.10-12 In this paper, a full-scale experiment was undertaken to study the blast wave propagation of the natural gas VCEs of a 1422 mm diameter underground long distance natural gas transmission pipeline pressurized to about 12 MPa. The key objective of the work was to provide experimental data on the blast wave overpressure characteristics of the long distance natural gas pipeline failures in terms of the fire and explosion overpressure hazards, which will assist in the development and validation of theoretical predicted models of long distance natural gas transmission pipeline hazards. Furthermore, the new theoretical prediction models were proposed and the comparisons with available data from

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full-scale experiment were performed. Finally, this experimental case has been analyzed in detail using the PHAST simulation software, the target of the simulated study is to predict the probability and potential damage range to humans and surroundings based on corresponding established damage criteria. This paper developed a theoretical and technical foundation for the establishment of a complete and scientific risk assessment method for natural gas explosion of a long distance pipeline system. 2.

THEORETICAL METHOD There are two blast wave propagation patterns that allow the overpressure experienced to be

linked to the distance from the explosive charge in a straight forward manner.13-15 The first propagation pattern is the free field case, which considers that the blast wave propagates freely in the atmosphere. The second propagation pattern is the case of a confined explosion, which considers that the blast wave propagates inside a confined space that is strong enough to withstand the explosive charge impulse. Based on the concepts mentioned, the first pattern seems more consistent with the situation of our case. The free field pattern is indubitably the studied most, the scaling laws were derived, and Brode16, Baker17, Mills18, Henrych19 have proposed general and equivalent fitting laws that relate the maximum overpressure peak and blast wave attenuation to the distance from the explosive charge. By multiple comparison and analysis, it is considered that Henrych model and Mills model are more reasonable and suitable in this research. TNT equivalency method is widely used for vapor cloud explosion blast modeling, which is based on the assumption of equivalence between the flammable material and TNT. The equivalent mass WTNT is calculated by the following equation (Eq. 1) based on the total heat of combustion of flammable material. =

(1)

where η is an empirical explosion efficiency, W the mass of flammable material, Qc the heat of combustion of flammable material, QTNT is the combustion of TNT, and WTNT is weight of TNT in kg. It is mentioned that the explosion efficiency becomes 2% to 15% for gas deflagrations. The effects of explosion can be evaluated by the reference experimental data of TNT of the equivalent mass. In this model, the scaled distance Z is given as Eq. (2) using WTNT1/3, and the evaluation can be performed conveniently. =

⁄

(2)

where R is the distance from the central point of gas explosion. The prediction is given as the semi-empirical curves on the coordinate system of the scaled distance Z and maximum overpressure Pm. Henrych19 proposed one of the most common law for blast wave attenuation in the free field of natural gas explosion, which is expressed as follows: Δ | =

."#$ %

+

'.' "

%( +.4 %

−

−

% ".*$+

".++$ %

".*'#

%(

+

+

+

%, $.*$

."'" %(

".""+$'

%

+

./ 0.05 ≤ ≤ 0.3

./ 0.3 ≤ ≤ 1

*.$66 %

./ 1 ≤


(3)

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Mills18 investigated the applicability of Sachs’ scaling law to gas explosions in free spaces for overpressure up to 0.1 MPa, combined with the similarity theory and simulation model method, Mills proposed to simplify the well-known free field decay laws for gas explosion by modifying the evaluation distance. The corrected TNT explosion blast wave overpressure-distance decay relationship can be expressed as: Δ |7899: =

"."6 %

−

". %(

+

.##$ %

(4)

The set of theoretical equations mentioned above provides a tool for evaluation of physical explosion in the natural gas pipeline. Accuracy and usability of the proposed theoretical prediction were tested by using full-scale natural gas experiments described in the following section. 3.

EXPERIMENTAL ARRANGEMENT

3.1 Test facility The experiment was conducted at a full-scale explosion testing ground in Kumul of China. This testing ground is the largest full-scale explosion experimental ground in Asia, it covers an area of 2.4 square kilometers, including the blast testing area, auxiliary production area, experimental equipment area, and its main functions can be meet to various pipeline testing requirements, as shown in Figure 1.

Figure 1. The testing pipeline and testing pole in full-scale experimental ground.

The test facility comprised a large natural gas tank truck and two pressure vaporizers feeding a 1422 mm diameter pipeline which is made of X80 steel, as indicated in Figure 2. The testing pipeline is installed with crack arresters and anchors on the surface (shows in Figure 3), which is guaranteed to fix the testing pipeline. The blast testing area have to set up gasification pressure equipment and temperament analysis equipment, in the meantime, the blast testing area connected with auxiliary production area by connecting pipe nearly 2000 m long distance with the diameter of 60 mm. The testing pipeline is buried up to 1.5 m deep underground and the length is approximately 430 m with the thickness of 35.6 mm. In this experiment, about 80000 m3 of natural gas are filled into the testing


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pipeline with the design pressure is 20 MPa, however in reality, the actual pressure in the testing pipeline is approximately 12 MPa.

Figure 2. The testing pipeline with a diameter of 1422 mm which is made of X80 steel.

Figure 3. Schematic configuration of natural gas pipeline supply.

The leakage was on the central of testing pipeline with roughly 0.5 m long and 0.01 m wide, which was sealed to keep the testing pipeline pressure inside. Ignition was achieved by the aerial shell, in this experiment the aerial shell incendiary devices deployed at the ground level, it was controlled manually after cutting the leakage of testing pipeline. 3.2 Apparatus 3.2.1

Overpressure instrumentation The overpressure development within this natural gas explosion testing was measured using

piezoelectric pressure transducers with built-in FPG amplifiers were used, as shown in Figure 4. The reliability and sensitivity of the pressure transducers were higher than normal overpressure instrumentation. These had range of 0.001~200 MPa with a response time of 1 ms, and the upper limit of frequency range of 50~500 kHz. The pressure transducers had two sensitive surfaces which are made of ceramic, so that when the blast wave swept over any one of the surface, the overpressure data can be measured. The maximum overpressure associated with the testing pipeline rupture and ignition of the gas cloud were determined.


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Figure 4. FPG pressure transducers for this full-scale experiment.

Due to the natural gas explosion experiment was full-scale arrangement, the traditional near the ground explosion testing method was not applicable obviously, especially to high altitude vapor cloud explosion testing, and it needed to present a spatial three dimensional field testing plan. According to the estimated height and diameter of the vapor cloud explosion, the four lines of testing poles were built around as the center of the gas explosion testing pipeline, and along a line in the west perpendicular to the testing pipeline, as shown in Figure 5 and Figure 6.

Figure 5. 3D layout of this full-scale natural gas explosion experimental ground.


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Figure 6. Schematic of the testing pole with pressure transducers arrangement.

Starting at the position about 100 m from the center of testing pipeline, with a 50 m gap between each pole, which was installed five pressure transducers on it, all the instruments were directed towards the center of the testing pipeline, so that the omnidirectional data would be measured by totally 26 poles with 130 pressure transducers. The pressure transducers were calibrated using a PCB model 903B Pulse Calibrator (0~1 MPa range) using a 0~2 MPa Druck pressure calibrator as the static pressure source. The pressure transducers installations were shown as follow (Figure 7).

(a)

(b)

Figure 7. (a) Proposed experimental testing pole arrangement; (b) Pressure transducers installation on the testing pole.


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3.2.2

Data acquisition The overpressure data were recorded on a National Instruments (NI) high speed transient

recorder20 at a rate of at least 50 kHz and on digital pressure recorders (DPR). The NI data acquisition system was comprised of one NI data acquisition equipment, a charge amplifier and synchronous trigger which would be triggered manually, the whole system would be put into the three bunkers of testing ground, as shown in Figure 8. The DPR data acquisition system was a new type of integrating the signal trigger, data receiver, and signal processing and data acquisition equipment directly that can be triggered automatically with the ignition determination. Each DPR equipment would be placed under each transducer installation pole with battery-powered, as shown in Figure 9. A back-up recorder was also used to avoid both recording failure and over-ranging, by setting a higher recording range on the back-up recorder.

Figure 8. Data acquisition equipment of data acquisition room.

Figure 9. Digital pressure recorder.


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4.

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QUANTITATIVE ASSESSMENT

4.1 Software simulation PHAST is the world's most comprehensive process industry hazard analysis and consequence assessment software developed by DNV Software.21-26 PHAST examines the progress of a potential incident from the initial release to far field dispersion, including modelling of pool spreading and evaporation, and flammable and toxic effects. It’s able to simulate various source terms such as leaks, line ruptures, long pipeline releases and tank roof collapses in both pressurized and unpressurized vessels and pipes, which are combined with PHAST’s unified dispersion model to obtain desired consequence results 4.2 General Scenario In this simulation, we assume 80000 m3 of natural gas is stored in a long distance pipeline with the pressure of 12 MPa, the basic scenario is an instantaneous release of natural gas from a hole located at the central top of the pipeline, 1.5 m below the ground. The theoretical basis of this approach on natrual gas dispersion is that after the formation of the plume, the natural gas concentration would remain unchanged in a continuous steady state release. In addition, the wind speed, wind direction and atmospheric stability are considered as constant variables in a specific release scenario. The simulation result of PHAST includes the overpressure of gas explosion, distance downwind from the gas explosion point, the distance crosswind from the gas explosion point, the expected impact time and the time left before hazardous gas plume reaches the distant areas. To generate enough scenarios for this numerical test, more specifics of the parameters are listed in Table 1. Table 1. Main parameters setting in PHAST simulator. Number

Parameter

Value

1

Length of pipeline

430 m

2

Diameter of pipeline

1422 mm

3

Thickness of pipeline

35.6 mm

4

Burial depth of pipeline

1.5 m

5

Material of pipeline

X80 steel

6

Gas composition

Natural gas (methane)

7

Volume of gas

80000 m3

8

Design pressure

12 MPa

9

Temperature

10 ℃

10

Wind speed

5 m/s

11

Wind direction

Northeast

12

Soil property

Gobi Desert

13

Leakage size

0.5 m×0.01 m

4.3 Blast wave damage criteria The fatalities, which are the degree of damage to humans and surroundings, were applied based on the following criteria (Table 2 and 3).27-29 Traditionally, several common criteria are currently available for blast wave damage of gas explosion, which are overpressure criterion, impulse criterion and overpressure-impulse criterion. The correlation criterion is used to calculate the correlation degree


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based on the difference of parameters in an accident. In this research, overpressure criterion is applied to calculate and classify different blast wave damage zones which are dead zone, serious injury zone, slight injury zone and safe zone. The overpressure from the gas explosion is classified with these zones which are 0.075 MPa, 0.045 MPa, 0.025 MPa and 0.01 MPa. Table 2. Overpressure injury criteria for humans. Overpressure (MPa)

Injury level

＞0.075

Fatal

0.045~0.075

Serious

0.025~0.045

Moderate

0.01~0.025

Slight

＜0.01

Safe

Table 3. Overpressure damage criteria for construction.

5.

Overpressure (MPa)

Damage level

＞0.76

Collapsed buildings

0.05~0.076

All doors and windows were damaged

0.03~0.05

Most of doors and windows were damaged

0.012~0.03

A few of doors and windows were damaged

0.002~0.012

Only windows were damaged

＜0.002

Basically no damage

RESULTS AND DISCUSSION After leakage, the natural gas would release into the atmosphere from the break of the testing

pipeline, then ignition which caused a deflagrated combustion started in the central point of the testing pipeline, and the flame accelerated around the leakage point and was transformed into detonation in open space. The ignited released gas expanded quickly forming a fireball which rose as it expanded reaching a maximum size of more than 220 m, occurring about 5 s after the rupture. The fireball burned stably and the flame was spherical, between the times of about 6 s to 13 s, while the effective flame temperature was above 2000℃. Thereafter the fireball left the ground and the explosive mushroom cloud rose up to the sky gradually, this was due to the a considerable heat release from the fireball which made the internal flammable gas vapored, resulting the explosive fireball lighter. The fireball then burned out with time of probably 50 s, but the flame on the testing ground continued to increase, and the flame was yellow and luminous with a small amount of black smoke which was produced as the fireball burned out. The fire overall gradually decreased in length with time and burned out completely after 3 min. An explosive gap with the length of approximately 100 m on the central of testing pipeline, as shown in Figure 10.


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Figure 10. The testing pipeline was cracked in the natural gas explosion experiment.

5.1 Comparison of theoretical and experimental data TNT equivalency elemental concept is based on the assumption of equivalence between the flammable material and TNT, so the evaluation of WTNT was made by TNT equivalency method under the condition that the empirical explosion efficiency η is constant. During the process of theoretical calculation, based on the extensive research work of the gas cloud explosion accidents, we assumed that the value of explosion efficiency η is 3%. Furthermore, in this experiment, there was natural gas with the volume of approximately 80000 m3 in the testing pipeline, which can be converted to the equivalent of 57143 kg of the flammable material in this theoretical calculation. Thus, we can figure out the corresponding blast wave overpressure of this natural gas explosion by Henrych model and Mills model, respectively. The overall results and comparisons between the experimental and theoretical calculations are shown below (Table 4). Table 4. Comparison of the experimental data and theoretical predictions of the overpressure peaks. Distance from explosion point(m)

Experimental data(MPa)

Δ | (MPa)

Δ |7899: (MPa)

100

0.263

0.0523

0.0616

150

0.094

0.0268

0.0282

200

0.0613

0.0173

0.0180

250

0.0491

0.0125

0.0133

300

0.0259

0.0097

0.0107

400

0.0187

0.0079

0.0089

As Table 4 displays, the TNT equivalent charge which was calculated through TNT equivalency method achieved a clean value of 22653 kg, and the rule of blast wave overpressure change with the distance from central of testing pipeline is presented in the Table 4. To verify these predicted models for blast wave overpressure of natural gas explosion, we performed the full-scale explosion testing and


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some available data were measured in the experiments. As can be noted in Figure 11, the blast wave overpressure peak in this experiment occurs nearly 100 m from the explosion point, and the maximum overpressure value recorded by pressure transducers is 0.263 MPa, meanwhile at the same distance, the theoretical predicted value by Henrych model and Mills model are 0.0523 MPa and 0.0616 MPa, respectively. More markedly results can be represented in Figure 10 as follow.

Figure 11. Comparison of the experimental data and theoretical results.

As shown in Figure 11 above, for the theoretical prediction in this case, the calculated value by Henrych model agrees well with the evaluated value by Mills model, and in the near field of explosion, the overpressure predicted result by Mills model seems a little bit higher. However, compared with the experimental results in this case, the theoretical calculated values underestimate the experimental data, and the overpressure measured by sensors are much larger and about five times higher than theoretical calculations. It should be noted that essential differences exist between VCEs and TNT explosion, there are three aspects of the differences. The first aspect involves the explosive source, the volume of which will increase during the VCEs process, but it is always ignored in TNT explosion. The second one relates to the explosive energy which release instantaneous, whereas the energy release rate in VCEs should be limited. The last aspect is blast wave propagation velocity which is attenuated quite fast in TNT explosive process even with the blast wave strength increasing, but during the gas deflagration to detonation transition (DDT) in the VCEs process, the effect of positive blast wave pressure limits relatively shorter in duration while the negative pressure lasts for a long time. As a result of the differences between these two explosions described above, the theoretical prediction based on the previous TNT equivalency method is not suitable for accurately evaluating the blast wave overpressure of natural gas deflagration phenomena in the near field. Introduction of the empirical explosion efficiency can adjust the accuracy of the theoretical prediction, however, the value of the explosion efficiency cannot be determined systematically without experiments. 5.2 Modification of the previous theoretical model To accurately predict the blast wave overpressure generated from the VCEs, we put forward a new theoretical prediction method based on British Gas method 20, which is a modified TNT equivalency method. The British Gas method assumed that after the gas explosion happened, the blast wave overpressure would be between 0.2 MPa and 0.4 MPa in the near field, which is completely


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consistence with the experimental result. Compared with the traditional TNT equivalency method, the modified TNT equivalency method is more applicable and reasonable for the VCEs, especially for the near field of gas explosion. The modified TNT equivalency method assumed that the value of explosion efficiency η increases to 10%, furthermore, the scaled distance analysis represents a new scaling law for the blast wave intensity from the VCEs by assuming the constant is 3⁄8, so that Eq. (5) can be arranged to become the following scaling relation. =

⁄;

(5)

The theoretical predictions are recalculated now in Table 5 using this new modified method and plotted in Figure 12, it can be seen that all the modified theoretical predictions agree well with the experimental data. Especially in the near field, the theoretical calculations both by Henrych model and Mills model based on modified TNT equivalency method increase rapidly and are closer to the experimental data. Table 5. Comparison of experimental data and modified TNT equivalency method predicted results of overpressure peaks.

Δ | (MPa) Δ |7899: (MPa)

Distance from explosion point (m)

Experimental data (MPa)

100

0.263

0.2172

0.2928

150

0.094

0.0783

0.1033

200

0.0613

0.0471

0.0541

250

0.0491

0.0325

0.0350

300

0.0259

0.0244

0.0255

400

0.0187

0.0193

0.0200

Figure 12. Comparison of the experimental data and modified theoretical results.

To study further the relevance between theoretical results and experimental data, we plotted the curve of all the data. We can note in Figure 13 below that the theoretical results agree well with the line of experimental data, all the data are in the tendency to the exponential decay along with time and


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achieves the relative stability index in the explosive far field. In the near field, the blast wave overpressure prediction by Mills model is a little bit higher than experimental data while the calculation by Henrych model is slightly lower than the experimental result. When the blast wave propagate more than approximately 200 m, the overpressure curve trend of Henrych predicted is consistent with the experimental data curve. Similarly, the overpressure curve of Mills calculated trends close to the experimental when the blast wave propagate nearly 300 m.

Figure 13. Fitting curves of experimental data and modified theoretical results.

The Figure 14 demonstrated the curve of relative error between theoretical modified predictions and experimental data. It can be found that the average of relative error is 5.2% and the maximum is no more than 8.75%, it can be considered that the results are within an acceptable range. In addition, from the comparison of relative error between the theoretical predicted models, it is obvious that the Mills model shows more reliable and satisfactory results.

Figure 14. Curve of relative error between experimental data and modified theoretical results.


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The modified theoretical analysis is performed to seek the applicable correction predicted method, by which the blast wave intensity could be predicted using universal relationship between the large scaled distance and overpressure. The modification of the previous theoretical method is examined, using the result of the former section, the blast wave overpressure in VCEs can be predicted as Eq. (5). The modified predicted method is considered valid, as a result, blast wave overpressure of VCEs process in open space can be adequately predicted by the modified theoretical method. 5.3 PHAST simulation result The probability and potential consequences can then be combined to obtain the risk results. Sample dispersion prediction of blast wave overpressure change with distance by PHAST for this natural gas explosion shown in Figure 15. The result indicates that the blast wave overpressure will decline with the propagation distance increasing, a linear relationship between the overpressure attenuation and distance from the central explosive point. It is noticeable that the velocity is descending quicker in near field from 120 m to 200 m, the rate of decay is about 47.9%, and correspondingly, the overpressure attenuates steadily in the far field. Compared with the experimental data, the simulation values of the near field are a little smaller, for example the experimental value is 0.0613 MPa while the simulation value is approximately 0.0521 MPa at the same distance of 150 m. However, the simulation data are in good agreement with the theoretical predictions by modified models in the near field, such as the simulation value is about 0.372 MPa, which compared to the value of 0.0325 MPa by the modified Henrych model and the value of 0.035 MPa by Mills model, the deviation is acceptable. As the distance getting further from the center of explosive point with the range of nearly 300 m away, the simulation data can fit the experimental data and theoretical data very well in the far field. The comparison curve between experimental data, modified Henrych model prediction, modified Mills model prediction and PHAST simulation are shown in Figure 16.

Figure 15. Overpressure changing with distance in natural gas explosion simulated by PHAST.


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Figure 16. Comparison curves of experimental data, modified theoretical results and PHAST simulation.

The damage effect of blast wave overpressure on humans and surroundings have been discussed in the previous section, and the current degrees of damage are based on the blast wave overpressure injury criteria for human and construction. The blast wave overpressure contours for individual risk and societal risk curves can be obtained from PHAST, while the impact range can be determined depend on the two damage criteria for blast wave overpressure in VCEs. Figure 17 illustrates different blast wave overpressure contours by four colors, which represent four degrees of damage from blast wave overpressure in natural gas explosion. The red line shows the range of fatal zone with the overpressure of 0.075 MPa, which people in this area after the explosion happens will have a hypothetical life threatening. The population in this zone of overpressure intensity was likely to get death. The blue line shows the safety area ensures people exposure remain within safe state, and the overpressure value in this area is less than 0.01 MPa. The colored lines correspond to different risk levels by blast wave overpressure in this natural gas explosion are presented in Table 6 as follow. Analyzing the overpressure risk with range for human in this gas explosion in Table 6, we conclude that in the case of VCEs, a nearly 100% fatality is expected in a blast wave zone of about 160 m because of very short response time to escape from the blast wave overpressure. Relatively, there is no harm to people who stays beyond the range with the diameter of 545 m. Others will suffer from injures of different degrees when they are still at the scope with the cycle diameter between 160 m and 545 m on the explosion ground.


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Figure 17. Overpressure injury radial distance as estimated from PHAST for humans. Table 6. Overpressure injury level and range for humans. Overpressure (MPa)

Injury level

Impact range (m)

＞0.075

Fatal

＜160

0.045~0.075

Serious

160~214

0.025~0.045

Moderate

214~304

0.01~0.025

Slight

304~545

＜0.01

Safe

＞545

Figure 18 shows the simulation result of blast wave overpressure damage range for surrounding constructions from the gas explosion by using PHAST simulators. The values of the parameters such as the atmospheric conditions, filling ratio, etc. were taken for in the same way to the previous simulators. The definition of the damage level and the values of blast wave overpressure with the distance for the surrounding buildings are both listed in Table 7. It is found from the PHAST simulation result that the cyan zone shows the blast wave with overpressure of more than 0.076 MPa, which causes all the buildings collapsing from the explosive point to approximately 156 m after the explosion occurs. The affected seriously damage distance from the blast wave overpressure intensity of 0.05 MPa up to 0.076 MPa, the range is from the distance of 156 m with cyan colored line to 203 m with red colored line, in this zone, the blast wave overpressure will damage all the doors and windows. As the PHAST computations show, the blast wave overpressure intensity of 0.03 MPa (shown by yellow color ellipse) is found to span up to a radius of 275 m from the incident site as estimated from PHAST, the buildings in this zone of overpressure intensity was likely to get most damaged. The blast wave overpressure intensity of between 0.002 MPa (shown by blue color ellipse) up to 0.012 MPa (shown by green color ellipse), as estimated from PHAST, extends up to a distance of 480 m and 1755 m. In this zone, only a few windows would be broken by the blast wave overpressure. Whereas the distance of 1755 m (blue color ellipse) is found that entire buildings beyond the above radial zone is likely sufficient to guarantee no loss, where the blast wave overpressure value is estimated to be less than 0.002 MPa.


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Energy & Fuels

Figure 18. Overpressure damage radial distance as estimated from PHAST for constructions. Table 7. Overpressure damage level and range for constructions. Overpressure (MPa)

6.

Damage level

Impact range (m)

＞0.076

Collapsed buildings

＜156

0.05~0.076

All doors and windows were damaged

156~203

0.03~0.05

Most of doors and windows were damaged

203~275

0.012~0.03

A few of doors and windows were damaged

275~480

0.002~0.012

Only windows were damaged

480~1755

＜0.002

Basically no damage

＞1755

CONCLUSIONS In order to help iIn order to help investigate the risk in long distance natural gas pipeline, the

explosion experiment was carried out in a full-scale testing ground. Following the natural gas VCEs accident, significant experimental and theoretical predicted research commenced leading to a better understanding of the blast wave propagation. The theoretical prediction methods of the blast wave overpressure from natural gas VCEs have been examined in order to perform effective consequence analysis of accidental explosions. The results for the blast wave overpressure in the far field predictions by the theoretical predicted models based traditional TNT equivalency method, compared with the experimental data, having a certain deviation. For this reason, the modified theoretical prediction methods were developed in this study. From theoretical analysis of blast wave propagation in a natural gas VCEs, an evaluation equation of the blast wave intensity was derived. The equation was modified considering the effects of explosion efficiency and scaled distance analysis. The theoretical predictions by this modified models agreed well with the results of full-scale experiment, and the modified Mills model was found to give better accuracy and reliability than the modified Henrych model. Furthermore the risk assessment results of PHAST simulation for the actual natural gas explosion accident scenario of this natural gas long distance pipeline were correlated with the corresponding damage criteria from the accident site. The effects of blast wave overpressure in this natural gas explosion on humans and constructions were both compared and verified with the overpressure values and the damage range. The damage range of blast wave overpressure results obtained were used to evaluate the probability of injuries and building damage due to natural gas explosion accident in real


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scenarios. Based on the established damage criteria, we conclude that in this case of VCEs, a near 100% fatality is expected in a blast wave zone of within 160 m because of too short response time to escape from the blast wave overpressure, as well as seriously effect on the surrounding constructions and causing all the buildings collapsing with the radial distance of 156 m. Relatively, there is no any harm when the people stay beyond the scope with the ellipse diameter of 545 m and no damage to the surrounding buildings with the radial distance of 1755 m. The simulated loss corresponds to actual loss of life and property as verified from the full-scale experimental data, hence the risk assessment development of blast wave propagation in VCEs in open space with natural gas might be expected. ACKNOWLEDGEMENTS This paper is funded by CNPC of Urumqi, China. All the authors wish to gratefully acknowledge the sponsoring organizations, for having their supports without the full-scale experiments described in this paper would never have become a reality. REFERENCES [ 1 ] Acton, M.R., Baldwin, P.J., Baldwin, T.R., Jager, E.E.R.. The development of the pipesafe risk assessment package for gas transmission pipelines. In: Proceedings of International Pipeline Conference, 1998, Calgary, Canada. [ 2 ] Acton, M.R., Hankinson, G., Ashworth, B.P., Sanai, M., Colton, J.D. A full scale experimental study of fires following the rupture of natural gas transmission pipelines. In: International Pipeline Conference, 2000, Calgary, Canada. [ 3 ] Acton, M.R., Allason, D., Creitz, L.W., Lowesmith, B.J. Large scale experiments to study hydrogen pipeline fires. In: International Pipeline Conference, 2010, Calgary, Canada. [ 4 ] Merge. Modelling and Experimental Research into Gas Explosions. Overall Final Report of the MERGE Project, CEC contract STEP-CT-0111(SMA), 1994. [ 5 ] Harris, R.J., Wickens, M.J. Understanding vapour cloud explosions-an experimental study. In: Inst. of Gas Engineers 55th Autumn Meeting, Communication 1408 , 1989, London, UK. [ 6 ] Snowden, P. Critical design of validation experiments for vapour cloud explosion assessment methods. In: Intl. Conf. and Workshop on modelling and consequences of accidental releases of hazardous materials, 1999, San Francisco. [ 7 ] Harris, R. J. The Investigation and Control of Gas Explosions in Buildings and Heating Plant. British Gas and E and FN Spon, 1983, London. [ 8 ] Van Den Berg, A. C., Lannoy, A. J. Haz. Mat., 1993, 34, 151-171. [ 9 ] Van Wingerden, K. J. Loss Prev. Process Ind., 1994, 7(4), 295-303. [ 10 ] American institute of chemical engineers, 2000. Guidelines for Chemical Process Quantitative Risk Analysis. [ 11 ] TNO, Yellow Book, 2005. [ 12 ] W.E. Baker, P.A. Cox, P.S. Westine, J.J, Kulesz, R.A. Strehlow, Explosion Hazards and Evaluation, Elsevier, 1983. [ 13 ] Igra, O., Falcovitz, J., Houas, L., Jourdan, G. Review of methods to attenuate shock/blast waves. Prog. Aerosp. Sci, 2013, 58, 1-35. [ 14 ] Kim, W., Mogi, T., Dobashi, R. Effect of propagation behaviour of expanding spherical flames on the blast wave generated during unconfined gas explosions. Fuel, 2014, 128, 396-403. [ 15 ] Langlet, A., William-Louis, M., Girault, G., Pennetier, O. Transient response of a plate-liquid system under an aerial detonation: simulations and experiments. Comput. Struct, 2014, 133, 18-29. [ 16 ] Brode, H.L. Blast waves from a spherical charge. Phys. Fluids, 1995, 2(2), 217-229. [ 17 ] Baker, W.E., Cox, P.A., Westine, P.S., Kulesz, J.J., Strehlow, R.A. Explosion Hazards and Evaluation. Fundamental Studies in Engineering, 1983, New York. [ 18 ] Mills, C. The design of concrete structures to resist explosions and weapons effects. In: 1st Int. Conf. Hazard Prot.


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Comparative Study on Blast Wave Propagation of ... - ACS Publications

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