Hydrocarbon Ignition and Flammability Flashcards
(20 cards)
Lower Flammability Limit (LFL)
Just sufficient flammable material present in the air to be flammable.
Expressed as percentages by volume (% Vol.) of the flammable component in the gas mixture.
Upper Flammability Limit (UFL)
The maximum amount of flammable material present in the air to be flammable.
Expressed as percentages by volume (% Vol.) of the flammable component in the gas mixture.
Limiting Oxygen Concentration (LOC)
The oxygen concentration in a flammable mixture below which combustion is not possible. LOC is also known as Minimum Oxygen Concentration (MOC). LOC values varies for different inert gas e.g. N2, CO2, Argon.
Auto-Ignition Temperature (AIT)
The lowest temperature of a hot surface where a fuel/air mixture is able to self-ignite. AIT is strongly dependent on initial pressure. Therefore, it is reported for ambient pressure. For flame propagation to occur at lower temperature, the fuel/air mixture must remain in the flammable range.
Minimum Ignition Energy (MIE)
The minimum ignition energy required to ignite an optimum concentration of flammable material using a capacitative spark at a given P and T condition.
How is ignitability (Entzündbarkeit) of flammable atmosphere relatet to other properties?
The ignitability (Entzündbarkeit) of a flammable atmosphere is related to MIE (minimum ignition energy). A flammable mixture that is close to either the upper or lower limits (LFL/UFL) requires a higher amount of energy than the MIE to ignite.
Flash Point (FP)
The temperature of a liquid at which sufficient vapour is generated just above the liquid level in the air that can be ignited by an open ignition source (flame, spark) // The lowest temperature at which a liquid gives off vapours in sufficient amount to support ignition of a vapour/air mixture just above the liquid level.
How are products categorzied by FP? especially in company?
- Low Flash Product: Hydrocarbon with FP < 38°C (100°F)
- High Flash Product: Hydrocarbon with FP > 38°C (100°F) For safe handling and operation, hydrocarbon fluids are typically classified according to their FPs.
classification:
- The NFPA in North America
- The Energy Institute 15 (EI15) outside North America
Flammable Range for Hydrocarbon Gases/Vapours
Typically from 0.7% Vol. to 10% Vol. at ambient conditions (pressure and temperature).
Light Hydrocarbons: Wider flammable range for methane, ethane, ethylene, and especially acetylene.
Whats’s special about tjhe flammable range of Hydrogen?
Extremely wide flammable range of 4% Vol. to 75% Vol.
For comparision: for Hydrocarbon Gases/Vapours: Typically from 0.7% Vol. to 10% Vol. at ambient conditions (pressure and temperature).
Which additional hazard existis in mixtures or multiple flammable materials?
Atmosphere can be flammable even if each component is below its LFL.
Dust and flammable gas/vapour mixtures can also be flammable.
What is volatility of liquids? + example for a product with high volatility?
Defined by the ability to give off vapours and the amount at which this occurs. (Vapour Generation: Liquids give off vapours, increasing with temperature (saturated liquid vapour pressure equilibrium curve).
-> Gasoline is very volatile because it evaporates quickly and releases easily ignitable vapors. Water, on the other hand, is less volatile.
What is the correspondence of FP?
Lower Flammability Limit (LFL): FP temperature corresponds with the LFL concentration
Vapour Pressure: Liquids with low vapour pressures typically have high FPs; high vapour pressure liquids typically have low FPs.
When is a vapour satuarted?
Above UFL: Saturated vapour is over-rich (non-flammable).
How can over-rich vapour be flammable?
Saturation Time: Can take several days in large storage tanks.
Distance from Liquid Surface: Vapour concentration decreases without mixing, far from the liquid, vapour is not saturated.
Mixing with Air: Reduces vapour concentration at openings (vents, hatches) or during emptying.
-> Atmosphere could be flammable even if saturated vapour-air mixture is over-rich!!
When is a liquid flammable?
Above FP and under UFL Upper Flammability Limit (UFL)
When is a liquid too dilute (too lean) to be flammable
Below FP
What to consider for Hydrocarbons regarding potential hazards?
- Absorption: Specialized hydrocarbon fluids like ‘frac’ fluids or ‘lean oils’ absorb other hydrocarbons, changing their properties significantly.
- Hazard Changes: Contact with other hydrocarbons can alter the potential hazards of these fluids.
- Testing: Reused fluids must be tested to ensure their properties are still suitable for use.
- Explosive Mixtures: Chemicals and hydrocarbon-based liquids used in the oil and gas industry can create explosive mixtures, including well servicing chemicals, solvents, cleaning agents, hydraulic fluids, and lubricants.
What did the Permit to Work require during hot work?
Continuous (!) gas monitoring.
How does the vapour generation increase?
Liquids give off vapours, increasing with temperature (saturated liquid vapour pressure equilibrium curve).
