Presentation Transcript

1. quantitative Toxic hazard likelihood of damage based on exposure reduction by appropriate techniques Definitions - Toxicology Toxicology - entry of toxicants into organism - elimination from organism - effects on organism Industrial hygiene prevention or reduction of entry Toxicant - chemical agents - physical agents: particulates < 5 µm, noise, radiation Toxicity property related to effect on organism

2. Entry Ways for Toxicants ENTRY ROUTE CONTROL Ingestion mouth, stomach rules on eating, drinking, smoking Inhalation mouth, nose ventilation, hoods, protection equipment * Injection cuts in skin protective clothing * Dermal Absorption skin protective clothing * industrially most significant

3. Response to Toxicants When a set of organisms is exposed to a toxicant at a fixed concentration, a variety or responses is obtained, depending on a number of factors: Age of organism Sex of organism Health of organism Etc. Need a statistical way to represent response.

4. Response vs. Dose Average Response Not very useful Dose Better at low doses, much more useful Average Response Log ( Dose ) Can also use a probit transformation to change s-shaped curve into a straight line.

5. Threshold Limit Value TLV: worker’s lifetime 8 hours per day 40 hours per week Threshold Limits THRESHOLD DOSE: NO DETECTABLE EFFECT TLV - TWA * time weighed average TLV - STEL short term exposure limit TLV - C ceiling limit * ~ PEL Permissible Exposure Level ~ some toxicants have zero thresholds

6. Threshold Limits Values TLV-TWA (ppm) Carbon Monoxide: 50 Chlorine: 0.5 Formaldehyde: 1 Methyl Alcohol: 200 Methyl Ethyl Ketone: 200 Phosgene: 0.1 Turpentine: 100 ppm: parts per million by volume

7. Industrial hygiene Concerns conditions related to workplace injury and sicknesse.g: exposures to toxic vapors, dust, noise, heat, cold, radiation, physical factors, etc. ANTICIPATION expectation of hazard existence IDENTIFICATION presence of workplace exposure EVALUATION magnitude exposure CONTROL reduction to acceptable levels Chemical Plants & Labs:requires co-operation from industrial hygiene, safety & plant operations people

8. SOME POTENTIAL HAZARDS: HAZARD DATA: • volatile liquids • vapors • dusts • noise • radiation • temperature • mechanical • physical state / vapor pressure • TLV’s • temperature sensitivity • rate and heat of reaction • by-products • reactivity with other chemicals • explosion limits Identification Requires study of : • process design • operating instructions • safety reviews • equipment description • chemicals description MSDS’s CHEMICAL PROCESS OPERATING CONDITIONS OPERATING PROCEDURES RISK ASSESMENT: potential for hazard to result in an accident

9. Evaluation Volatiles monitoring air concentrations variation in time and place Time Weighted Average Continuous: ppm or mg/m3 Intermittent: Additive effect multiple toxicants: Equivalent Mixture:

10. Source Models • What: Describe how material escapes from a process • Why: Required to determine potential consequences of and accident Risk = f( Probability, Consequences )

11. What do Source Models Provide? • Release rate, mass/time • Total amount released • State of material: liquid, solid, gas, combination

12. P1 > P2 Source Model: Liquid thru a hole 1. Pressure drives liquid thru hole 2. Pressure energy converted to KE as liquid escapes 3. Frictional losses Orifice Discharge Equation

13. Dispersion Models What? Describe how vapors are transported downwind of a release. > 100 m Why? To determine the consequences Results: Downwind concentrations (x,y,z) Area affected Downwind distances

14. Dispersion wind PLUME PUFF place time & place continuous release instantaneous release DOWNWIND DILUTION BY MIXING WITH FRESH AIR ATMOSPHERIC DISPERSION - wind speed - atmospheric stability: vertical temp. profile - roughness ground: buildings, structures, trees, water - height release above ground level - momentum and buoyancy: effective height difficult

15. FIRE:Rapid exothermic, oxidation, with flame EXPLOSION:Higher energy release rate (mixture) pressure or shock wave Fires and Explosions } may trigger each other } Injuries / casualties Property losses Process interruption Thermal radiation, blast wave, fragments, asphyxiation, toxic products. EFFECTS REQUIRED KNOWLEDGE FOR PREVENTION Material properties Nature of fire and explosion process Procedures to reduce hazards

16. Fire Triangle FIRE TRIANGLE FUEL OXIDIZER IGNITION SOURCE Oxidant Fuel Ignition Source Oxidant may not be oxygen! For example, chlorine can oxidize.

17. Application of the Fire Triangle Fires and explosions can be prevented by removing any single leg from the fire triangle. Problem: Ignition sources are so plentiful that it is not a reliable control method. Oxidant Fuel No Fire Ignition Source Robust Control: Prevent existence of flammable mixtures.

18. Definitions - 1 LFL: Lower Flammability Limit Below LFL, mixture will not burn, it is too lean. UFL: Upper Flammability Limit Above UFL, mixture will not burn, it is too rich. Defined only for gas mixtures in air. Both UFL and LFL defined as volume % fuel in air.

19. Definitions - 2 Flash Point: Temperature above which a liquid produces enough vapor to form an ignitable mixture with air. Defined only for liquids. Auto-Ignition Temperature (AIT): Temperature above which energy can be extracted from the environment to provide an ignition source.

20. Definitions - 3 Minimum Oxygen Concentration (MOC): Oxygen concentration below which combustion is not possible. Expressed as volume % oxygen. Also called: Limiting Oxygen Concentration (LOC) Max. Safe Oxygen Conc. (MSOC) Others

21. Typical Values - 1 LFL UFL Methane: 5% 15% Propane: 2.1% 9.5% Butane: 1.6% 8.4% Hydrogen: 4.0% 75% Flash Point Temp. (deg F) Methanol: 54 Benzene: 12 Gasoline: -40

22. Typical Values - 2 AIT (deg. F) Methane: 1000 Methanol: 867 Toluene: 997 MOC (Vol. % Oxygen) Methane: 12% Ethane: 11% Hydrogen: 5%

23. Flammability Relationships Vapor Pressure Curve UFL UFL Liquid Vapor pressure / concentration Auto-ignition zone Gas LFL LFL Flash Point AIT Ambient Temperature Temperature

24. Explosions - Definitions Explosion: A very sudden release of energy resulting in a shock or pressure wave. Shock, Blast or pressure wave: Pressure wave that causes damage. Deflagration: Reaction wave speed < speed of sound. Detonation: Reaction wave speed > speed of sound. Speed of sound: 344 m/s, 1129 ft/s at ambient T, P. Deflagrations are the usual case with explosions involving flammable materials.

25. BLEVE BLEVE:Boiling Liquid Expanding Vapor Explosion Vessel with liquid stored below its normal boiling point Vapor Liquid Below liquid level - liquid keeps metal walls cool. Above liquid level - metal walls overheat and lose strength. After vessel failure, a large amount of superheated liquid is released, which will flash explosively into vapor. If the liquid is flammable, a fireball may result.

26. Most Important Concept • Chemicals have hazardous properties that can be well characterized and are well-understood. • Toxicity • Flammability • Reactivity • Others