Part 2.5 Dispersion Modeling Using ALOHA Dr. Arshad Ahmad Email: arshad@utm.my 1
Software Commonly used for Risk Analysis Software SAFETI SFU CAFTAN ETRA HAZSEC. HAZTRAC. PHAST. WHAZAN EFFECTS. DAMAGE PC-FACTS. ASAP FMECA ANEX Application Onshore Risk Analysis. Offshore Risk Analysis. Fault Tree Analysis. Event Tree Analysis. HAZOP Study. HAZOP Recommendation Tracking. Consequence Analysis. Consequence Analysis. Consequence (Effects) Modeling. Consequence (Damage) Modeling. Failure & Accident Databank. Event Tree Analysis. Failure Mode Effects & Criticality Analysis. Life Time Analysis & Failure Estimation.
Software Commonly used for Risk Analysis Software ALOHA CLASS RISK CURVES RISKA T E&P FORUM FACTS OREDA FRED EAHAP Application Consequence Analysis Hazardous Area Risk & Classifications TNO Individual & Group Risk computations Risk Analysis model of Health & Safety Executives, UK Hydrocarbon Leak & Ignition Database. TNO Frequency Estimation Database DNV Frequency Estimation Database Consequence Analysis software of Shell, UK Consequence modeling software of Energy Analysts Inc. US)
What is CAMEO? CAMEO is computer software primarily used: For chemical emergency planning For chemical response; and For regulatory compliance The overall CAMEO system is a suite of three separate, integrated software applications: CAMEO (Computer aided management of emergency operation) MARPLOT (Mapping application for response and planning of local operational task) ALOHA (Areal locations of hazardous atmosphere) Developed by: EPA s Chemical Emergency Preparedness and Prevention Office NOAA s Hazardous Materials Response and Assessment Division
CAMEO Answers Questions What hazards are at this site? Where is the hazard located? What is the chemical? What specific hazard(s) does it present? How can the hazard be mitigated?
Toxic Release Inventory Cameo Module Relationships Chemicals in Inventory/ Transit Storage Locations Chemical Information Facilities Screening & Scenarios Incidents Routes Special Locations Contacts Census Data Resources
ALOHA
What is ALOHA Air hazard modeling program Predicts how quickly chemical will escape from a tank, puddle, gas pipeline etc Model how gas travel downwind (include neutrally buoyant and heavy gas dispersion) Model fire and explosion (pool, jet, flash, BLEVE, VCE) Produces threat zone estimate, showing area of hazards (toxicity, thermal radiation) Threat zones can me mapped into MARPLOT, Google maps, Google earth 8
Example of ALOHA s Output Threat Zones Concentration at a point 9
GIS Compatible Output 10
Fire and Explosion
Pool Fire 12
Pool Fire 13
Jet Fire 14
Jet Fire 15
BLEVE Fireball Model 16
BLEVE Fireball Model 17
Flash Fire & Vapor Cloud Explosion Model 18
Flash Fire & Vapor Cloud Explosion Model Vapor cloud explosion major assumptions: Uses Baker-Strehlow-Tang methodology Flammable mass (0.9LEL - UEL) Explosion efficiency Detonation 100% Deflagration 20% Ignition options Hard ~10 6 Joules Soft ~1 Joule 19
Flash Fire & Vapor Cloud Explosion Model Vapor cloud explosion major assumptions: (cont.) Congestion options High area blockage ratio > 40% Low area blockage ratio < 10% 20
Flash Fire & Vapor Cloud Explosion Model 21
Example: Facility Siting Case Study 22
Example: Facility Siting Case Study Release through 3-inch relief valve leading to: Jet fire Flash fire Vapor cloud explosion Failure of storage vessel engulfed in flames leading to: BLEVE fireball 23
Facility Siting Case Study Jet Fire Results 24
Facility Siting Case Study Jet Fire Results 25
Facility Siting Case Study Jet Fire Results 26
Facility Siting Case Study Jet Fire Results 27
Facility Siting Case Study Jet Fire Results 28
ALOHA Scenario In a transportation accident at km 182 of Southbound North-South Expressway in Nilai, a 9000 Gallon tank truck carrying ammonia overturns and shears off a flange whose diameter is 4 inches. The size of the tank is 24 feet long and 8 feet in diameter. The tank contains liquid, which is stored at ambient temperature. The fill density of the tank is 75% by volume. The sheared-off flange creates a circular opening of about 3 inches in diameter, and it is located at 30% of the way to the top of the tank. At the time of the accident, the wind direction is NE (i.e. blowing from NE), the wind speed is 3 m/s, measured at 10 m height. The accident occurred on a highway near a small village. The weather is partly cloudy, 80% relative humidity, and the temperature is 32 degrees Celsius. 29
Dispersion Modeling 30
Meteorology and Boundary Layer Wind factors Vertical temperature structure & stability Surface roughness Meteorological instrumentation 31
Source Term, Dilution & Plume Rise Release parameters from source Release parameters of the chemical Plume rise Release height for buoyant sources Volume & area point sources Building effects 32
Dispersion of Neutrally Buoyant Gases The plume is not rising nor sinking Equal probability of spreading in different directions Neutrally buoyant gases are described using Gaussian statistics or normal distributions 33
Dispersion of Heavy Gases Types of heavy gases Gravitational spreading Phases of heavy gas dispersion Release Transition Dispersion 34
End of Lecture 35