Mathematics 108 Mathematical Modeling in the Environment Chapter 4 - - PDF document

Mathematics 108 Mathematical Modeling in the Environment

Chapter 4 Hazardous Materials Management 4.1 Background Episodic Events: 1979 - Three Mile Island - Harrisburg, Penn- sylvania Partial meltdown of radioactive core

Lessons:

• Technological systems can fail in unexpected

ways

• Need to plan for response to low probability

emergencies

• Even experts make mistakes

December 12, 1984 - Bhopal, India - Union Carbide Plant (Union Carbide headquarters were in Danbury; severe impact on Connecticut) Toxic gas cloud killed or severely harmed thou- sands - 3,000 dead April, 1986 - Chernobyl, Ukraine nuclear plant

(Some immigrants to Waterbury area have had health problems possibly associated with explo- sion.) Two explosions, fire, radioactivity detected in Scandinavia November, 1986 - Basel, Switzerland - Fire in chemical plant Released thousands of tons of chemicals into Rhine, damage reached the Netherlands. 1988 - Pennsylvania - Million gallon diesel oil tank failed Oil entered Susquehanna River, moved to Ohio River 1989 - Alaska - Exxon Valdex

Tanker spill released 232,000 gallons of crude

• il within a few miles of shore.

Consequences:

• Public pressure
• Financial concerns
• Regulatory developments – Superfund, Re-

source Conservation and Recovery Act (RCRA) Industry Reactions:

• More extensive and uniform written policies

and procedures

• Formal oversight processes

• Quantitative methodologies for addressing

probabilities and consequences of undersir- able occurrences

• Identification of “critical operating param-

eters” to trigger action

• Extensive emergency planning

Regulatory Reactions:

• Widespread availability of Material Safety

Data Sheets (MSDS) listing properties, haz- ards and protective measures

• Formation of local and statewide emergency

planning committees

• Strict reportability requirements

• Mandated environmental audits and quan-

titative risk analysis

• Modified requirements for transport of haz-

ardous materials

Technical Assistance Made Available:

• “Orange Book” – first responder’s guide

to dealing with emergencies

• Risk analysis computer programs
• 1. ARCHIE - Automated Resource for Chem-

ical Hazard Incident Evaluation

• 2. CAMEO - Computer-Aided Management
• f Emergency Operations

(a) ALOHA - Areal Locations of Hazardous Atmospheres (b) MARPLOT - Mapping Application for Response, Planning and Local Oper- ational Tasks

• Programs to help business evaluate oppor-

tunities for reducing their use of hazardous chemicals

4.1 Exercises - Page 108

4.2 Hazardous Materials Handling Practices and Potential Accidents Transportation Concerns

• Tank trucks and railway cars
• Trucks containing chemicals
• Pipelines
• Planes carrying hazardous cargoes.

Dominant Hazards

• Pool fire
• Vapor cloud fire

• Vapor cloud explosion
• Flame jet
• BLEVE – Boiling Liquid Expanding Vapor

Explosion

• Toxic vapor cloud
• Suffocation

Table 4-1 Examples of hazmat accident initia- tors (Page 110)

4.3 Physical Principles and Background 4.3.1 Basic Physics and Chemistry Atomic number - number of protons in nucleus

• f an atom - determines basic chemical prop-

erties Atomic weight - number of protons plus num- ber of neutrons - averaged Molecular weight - sum of atomic weights of individual atoms

4.3.1.2 Physical Properties of Matter Three states: solid, liquid, gas Main concern here: liquids, gases, transition from liquid to gas Density: mass per unit volume Specific gravity: ratio of density to density of water Evaporation

• 1. Rate of evaporation is proportional to sur-

face area. Evaporation occurs as molecules near the surface have sufficient kinetic en- ergy to break through the surface.

• 2. Rate of evaporation increases with temper-

ature.

Boiling - vapor pressure in higher than atmo- spheric pressure - chemical can enter vapor form from throughout the liquid 4.3.1.2 Exercises Page 119

4.3.2 Characterization of Flammable Vapor Haz- ards Flammmable Limits - Lower Flammmable Limit

• Upper Flammable Limit (Sometimes referred

to as Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL)) Expressed as percentage of molecules in the vapor space If the percentage of molecules in the vapor space is either above the UFL or below the LFL, then the vapor will not burn. Flash Point - Temperature at which the per- centage of vapor exceeds the LFL Volatile - Materials that readily evaporate 4.3.2 Exercises Page 123

4.3.3 Characterization of Toxicity Hazards Acute Toxic Hazards, Chronic Toxic Hazards TLV - Threshold Limit Value - Level of accept- able exposure (Based on recommendations by the American Conference of Government In- dustrial Hygienists, ACGIH) Subdivided into:

• Under normal working conditions
• Daily time-weighted averages
• Short term exposures (generally 15 min-

utes) IDLH Values - Immediately dangerous to life or health (Published by NIOSH, National Institute

for Occupational Safety and Health) Generally expressed in PPMs, parts per million; some- times in mass per unit volume Chemical Principles

• 1. Under fixed conditions of pressure and tem-

perature, a given volume of gas will con- tain the same number of molecules of any gaseous substance whether the molecules are small, light molecules or larger, heavy molecules.

• 2. Avogadro’s Number:

6.022 × 1023. This is the number of molecules contained in M grams of a substance with molecular weight M.

• 3. One mole of a gas under standard temper-

ature and pressure conditions occupies a volume of 22.4 liters.

• 4. The number of moles of a gas is the quo-

tient of its mass (in grams) divided by its molecular weight.

• 5. The number of molecules of of a gas is the

product of the number of moles × Avo- gadro’s Number. These principles enable one to translate be- tween mass per unit volume and parts per mil- lion. 4.3.3 Exercises Page 128

4.4 Typical Quantitative Issues Three scenarios Table 4-6 – Selected information needs – Page 131 From First Scenario (Derailment, possible chem- ical leak) Questions:

• Vapor concentrations–in various directions

and at various distances

• Flammable and toxicity limits
• Potential for flammmable or toxic vapor

cloud to extend a distance from the ac- cident

• Other hazards?

Benefit of software on site – can give fast ac- cess to useful quantitative estimates To use software on site, need modeling spe- cialist on site, with computers and programs in the emergency vehicles From Second Scenario (Nearby manufacturing plant has chemical storage tanks) Interesting range of participants: fire, police, hazmat team, EPA, FEMA, environmental agen- cies, transportation departments, civil defense, public works, hospital emergency room, local companies, private contractors, university con- sultants, school department Modeling can play a significant role in local planning and training when analyzing hazards

• f a hypothetical incident

From Third Scenario (Develop priorities for haz- ardous chemicals shipped in bulk) Different approaches are possible There are several distinct levels at which mod- els can be useful, including site-specific response, long-range planning, training and prioritization 4.4 Exercises Page 134 Assignment: Question 1

4.5 Structure and Use of Hazmat Computer Modeling Packages Principal Input:

• Chemical involved
• Leak conditions – eg source, size of open-

ing affects rate of leakage

• Duration of leak
• Liquid pool area limitations – size may be

constrained

• Weather conditions – temperature, wind

Chemical Data (MSDS) – may be included in software

• Dominant hazards
• Hazardous concentration levels
• Physical and chemical properties
• Hazardous reaction or combustion products

Geographic Data

• Map of area
• Sensitive facilities
• Storm sewers and water bodies

Models

• Tank or pipeline discharge rate
• Pool size
• Evaporation rate
• Vapor dispersion
• Thermal radiation
• Flame jet distance
• Explosion overpressures
• Tank pressurization (from heat)
• BLEVE impacts

Output

• Hazard distances and directions
• Concentrations as functions of time and lo-

cation

• Concentration ispleth map
• Hazard zone map

Considerations

• Units
• Chemical data

• Feasible scenarios – make sure your input

is reasonable

• Care with illogical input requirements
• Adapting the model – it may, more likely

will, not fit the situation exactly Test Results:

• Against physical intuition
• Against rough estimates
• Against additional model calculations – vary-

ing the input slightly and checking whether the output changes as expected

4.6 The Analysis of Typical Scenarios We will go through several of these in class and in the lab. 4.6 Exercises Page 150