1. Safety Determine conditions where fires and /or explosions can occur.
Develop estimates for upper/lower flammability limits in mixtures
Utilize inerting to prevent fires/explosions.

2. Combustion/Fire/Explosion

3. Where Does Reaction Occur?
In gas phase where ignition source, oxygen and fuel coexist.
Can be autocatalytic under certain conditions.
May not need ignition source if temperature is high enough.

4. Types of Reactions Slow Oxidation Fire Deflagration/Explosion
Energy can be absorbed by surroundings without increase in temperature.
Fire
Energy released can be dissipated by environment with an increase in temperature to a stable point.
Deflagration/Explosion
Energy released cannot be fully dissipated by environment and temperature continuously increases.

5. Definitions Flash Point Temperature Fire Point Temperature
Enough fuel exists in air to create a flammable mixture. Will “burn out”.
Fire Point Temperature
Enough fuel exists in air to create a sustainable flammable mixture.
Flammability Limits
Volume percent ranges of fuel in air where burning occurs.

6. LFL Lower Flammability Limit
Partial pressure of fuel is too low to keep reaction going
UFL Upper Flammability Limit
Partial pressure of oxygen is too low to keep reaction going

7. Sources for LFL/UFL
MSDS sheets where data was obtained experimentally.
Mixtures of Fuels
Can be calculated with known LFL/UFL of all components

8. Calculating LFL/UFL of Mixtures

9. 20:80 Hexane/Heptane Liquid at 25 oC
Assume Liquid is in equilibrium with air in headspace
Calculate mole fraction of each component using Raoult’s Law or suitable model.
Calculate LFL/UFL of mixture

11. Temperature Dependence of LFL/UFL

12. T = 20 oC

13. Pressure Effects

14. Flammability Diagrams
Compression and Ignition

16. 40% Nitrogen
40% Fuel
20% Oxygen

17. Original Mixture
40% Nitrogen
40% Fuel
20% Oxygen
Dilute with Air

18. Original Mixture
40% Nitrogen
40% Fuel
20% Oxygen
Dilute with Air
Air Added
Original Fuel

19. Constructing Flammability Diagram Fuel + zO2  CO2 + H2O
1. Draw Air Line
2. Enter LFL & UFL
Determine z
LOC = zLFL (use data, if available)
UFL
LFL

21. Constructing Flammability Diagram Fuel + zO2  CO2 + H2O
Add Stoichiometric Line
Get Pure Oxygen LFL and UFL (if available)
LOC
UFL
LFL

22. Constructing Flammability Diagram Fuel + zO2  CO2 + H2O
7. Construct Curve
LOC
Flammable
Region

24. Compression of Gases

25. Acrylic Acid Process Compressor Section

26. Safety (MSDS) data for hexane
Physical data
Appearance: colourless liquid Melting point: -95 C Boiling point: 69 C Vapour density: 3 (air = 1) Vapour pressure: 132 mm Hg at 20 C Specific gravity: Flash point: -10 F Explosion limits: 1.2% - 7.7% Autoignition temperature: 453 F