Intensity level kWm Times Probit value Lethality level

4.5.4.2 Overpressure Impacts

The purpose of the explosion impact models is to predict the impact of blast overpressure and projectiles on people and objects. Explosion effects have been studied for many years, primarily with respect to the layout and sitting of military munitions stockpiles. Explosion effects are classified according to effects on structures and people [2].

4.5.4.2.1 Effect Blast on Equipment and Structures

Explosion overpressure level and damage effect on structures are shown in Table 4-11. Overpressure duration is important for determining effects on structures. The positive pressure phase of the blast wave can last from 10 to 250 ms, or more, for typical VCEs. The same overpressure level can have markedly different effects depending on the duration [2]. Eisenberg et al. (1975) provide a simple probit model to describe the effects on structures.

Blast Damage Tables

Peak Overpressure (x10A5 Pa)

Fig. 4.16 Peak Overpressure impacts on structures

Peak Overpressure (x10A5 Pa)

Fig. 4.16 Peak Overpressure impacts on structures where Y is the probit and p is the peak overpressure (Pa). The probit, Y, can be converted to a percentage using Eq. (4-7), as shown in Fig.4.16. The percentage here represents the percent of structures damaged.

_Table 4-11 Explosion overpressure level and damage effects on structure [2]_

Overpressure (bar) Damage produced by blast effect

0.0207 No considerable damage except shattering of few glass panes

0.1379 Partial collapse of buildings

0.2068_Steel framed building distorted and pulled away from the foundation

4.5.4.2.2 Blast Effects on People

The purpose of the model is to determine the fatality probability of the occupants of buildings subject to blast loading. This is dependent on the level of blast loading, the type and construction of the building. In general, three categories of blast induced injury are identified:

(1). Primary injury is due directly to blast wave overpressure and duration (Table 4-13). The location of most severe injuries is where the density differences between adjacent body tissues are greatest, i.e. the lungs, the ears, the abdominal cavity, the larynx and trachea.

(2). Secondary injury is due to building collapse and impact by missiles produced as results of the explosion. This give rise to laceration, penetration and blunt trauma.

(3). Tertiary injury is due to displacement of the entire body followed by high decelerative impact loading which is when broken or fractured limbs can occur.

A study performed by [101] shows that the secondary effects are the dominant cause of fatalities. Primary and tertiary are less important at the overpressure levels considered, although impairment of hearing or lung damage may effects the ability of people to escape from collapsed buildings.

Biogas Equipments

Peak Overpressure (x10A5 Pa)

Fig. 4.17 Peak overpressure of hydrogen explosion on man

Peak Overpressure (x10A5 Pa)

Fig. 4.17 Peak overpressure of hydrogen explosion on man

Eisenberg et al. (1975) provide a probit for fatalities as a result of lung hemorrhage due to the direct effect of overpressure,

where Y is the probit and p is the peak overpressure (Pa), and is plotted in Fig. 4.17. The probit equation also shows that it requires relatively high blast overpressures (>1 hPa) to produce fatality (primarily due to lung hemorrhage). Another probit equation was developed by the HSE [92], based on peak overpressure:

Quest [93] used the explosion/lethality relationship for the Canvey study as shown in Table 412.

Table 4-12 Hazardous explosion overpressure level [93]

HSE Probit

Peak Overpressure (bar)

Fatality (%)

1

0.2

1

5

0.9

50

7

3.0

95

Table 4-13 Summary historical data on damage to humans from air blast effects [101]

m . , Peak overpressure

Eiiects on people (mbar)

Annoying noise of continuous type at 10-15 Hz and 137 dB 1.4

Loud noise at 143 dB 2.8

Sound 'note' as an unusual event - an explosion 0.34

Threshold for temporary loss of hearing 13.8

Threshold for eardrum rupture 138

50% eardrum rupture threshold 331

Threshold of skin laceration by missiles 69 - 138

Personnel knocked down or thrown to the ground 103-200

Possible death by persons being projected against obstacles 138

Low personnel risk when inside a resistant structure 69

50% probability of eardrum rupture 345-483

90% probability of eardrum rupture 689-1034

Threshold of internal injuries by blast 483

Serious missile wounds giving about 50% fatality 276 - 345

Serious missile wounds giving near 100% fatality 483 - 689

Threshold of lung haermorrhage 827-1034

50% fatality from lung haemorrhage 1379 - 1724

99% fatality from lung haemorrhage 2068 -2413

People standing up will be thrown a distance 552 - 1103

People lying up on the ground are picked up and hurled about 827 - 1655

Immediate blast fatalities_4826 - 13,790

Analysis of the blast effects on people are highly uncertain as they are based on injury models developed from condensed phase explosions. The probit approach could not be used due to the small distances involved. Therefore the study took a conservative approach, as shown in Table 4-14, considering that all or a proportion of personnel in the vicinity of an explosion will be fatalities.

_Table 4-14 Fatality probability for explosion used in the study_

(bar) Damage produced by Blast Eiiect J

0.0207 No considerable damage except shattering of few glass panes 0.01

0.1379 Partial collapse of Buildings 1

0.2068 Steel framed building distorted and pulled away from the foundation 10

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  • anette
    What is the effect of overpressure on fermentation?
    6 years ago

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