Page 334 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Hazard zone calculations 14/31 1
Table 14.32 Representative yield factors Flume jets
Vapor cloudfire and/orfireball-in which a cloud encoun-
Substance Yield factor ters an ignition source and causes the entire cloud to com-
bust as air and fuel are drawn together in a flash fire
Butadiene 0.03 situation.
Carbon monoxide 0.03 Liquidpoolfires-not thought to be a very high potential for
Ethane 0.03
Hydrogen 0.03 HVL releases unless ambient conditions are cold a liquid
Methane 0.03 pool of flammable material could form and create radiant
Methanol 0.03 heat hazards.
N-Butane 0.03 Vapor cloud explosion-
Propane 0.03
Styrene 0.03 Because precise modeling is so difficult. many assumptions
Toluene 0.03 are often employed. Use of conservative assumptions helps to
Vinyl chloride 0.03 avoid unpleasant surprises and to ensure acceptability of the
Ethylene 0.06
Propylene oxide 0.06 calculations, should they come under outside scrutiny. Some
Acetylene 0.19 sources of conservatism that can be introduced into HVL haz-
Methyl acetylene 0.19 ard zone calculations include
Vinyl acetylene 0.19
Overestimation of probable pipe hole size (can use full-bore
Source: "ARCHIE (Automated Resource for Chemical Hazard lncident rupture as an unlikely, but worst case release)
Evaluation)," prepared for the Federal Emergency Management Overestimation of probable pipeline pressure at release
Agency, Department of Transportation, and Environmental Protection (assume maximum pressures)
Agency, for Handbook of Chemical Hazard Analysis Procedures
(approximate date 1989) and software for dispersion modeling, ther- Stable atmospheric weather conditions at time of release
mal, and overpressure impacts. Ground-level release event.
Maximum cloud size occurring prior to ignition
Extremely rare unconfined vapor cloud explosion scenario
Highly volatile liquids with overpressure limits set at minimal damage levels
Overpressure effects distance added to ignition distance
HVL releases are complex, nonlinear processes, as discussed in (assume explosion epicenter is at farthest point from
Chapter 7. Hazards associated with the release of an HVL release).
include several flammability scenarios, an explosion potential,
and the more minor hazard of spilled material displacing air These conservative parameters would ensure that actual
and asphyxiating creatures in the oxygen-free space created. damage areas are well within the hazard zones for the vast
The flammability scenarios of concern include the following majority ofpipeline release scenarios. Additional parameters
(previously described): that could be adjusted in terms of conservatism include
mass of cloud involved in explosion event, overpressure
damage thresholds, effects of mixing on LFL distance,
Table 14.33 Expected damage for various levels of overpressure weather parameters that might promote more cohesive
cloud conditions and/or cloud drift, release scenarios that do
Peak overpressure not rapidly depressurize the pipeline, possibility for sympa-
(psW Expected damage thetic failures of adjacent pipelines or plant facilities,
ground-level versus atmospheric events, and the potential for
0.03 Occasional breakage of large windows under stress
0.3 Some damage to home ceilings; 10% window a high-velocity jet release of vapor and liquid in a downwind
breakage direction.
0.5-1.0 Windows usually shattered; some frame damage
1 .0 Partial demolition ofhomes; made uninhabitable Hazard zone defaults
2.0 Partial collapse of home wallsiroofs
2.0-3.0 Nonreinforced concrete/cmder block walls In the absence of detailed hazard zone calculations, some
shattered default distances can be set based on regulatory requirements
2.5 50% destruction of home brickwork or conservative fixed distances. For example, a type of
3.W.O Frameless steel panel buildings ruined
5.0 Wooden utility poles snapped hazard zone for a natural gas pipeline could be based on
5.0-7.0 Nearly complete destruction of houses generalized distances from specific receptors such as those
IO. Probable total building destruction given in Table 14.34. These are actually "distances of con-
14.5-29 .0 Range for 1-99% fatalities among exposed cern," rather than hazard zones, since they are based on
populations due to direct blast effects. receptor vulnerability rather than damage distances from a
pipeline release.
Source: "ARCHIE (Automated Resource for Chemical Hazard lncident Case Study C uses a default 1250-ft radius around an 18-in.
Evaluation)," prepared for the Federal Emergency Management
Agency, Department of Transportation, and Environmental Protection gasoline pipeline as a hazard zone, but allows for farther dis-
Agency, for Handbook of Chemical Hazard Analysis Procedures tances where modeling around specific receptors has shown
(approximate date 1989) and software for dispersion modeling, ther- that the topography supports a larger potential spill-impact
mal, and overpressure radius.