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April 12, 2025 11:51 PM

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• Process and Equipment Integrity
• Training and Performance
• Fires and Explosions

This diagram illustrates the Fire Triangle, a fundamental concept in fire safety and chemical
process safety.

The Fire Triangle

The triangle shows the three essential components required for a fire to occur:
1. Fuel – Any combustible material (e.g., gas, wood, oil).
2. Air (Oxygen) – Supports combustion; usually from the atmosphere.
3. Ignition Source – A heat or spark source to start the fire (e.g., open flame, static
electricity, hot surface).

Key Principles
• ✅ Fire occurs only when all three elements are present and in the right proportions.
➤ This is shown in the complete triangle labeled “Fire: When All Sides Are Connected.”
• ❌ No fire occurs if any one of the three elements is missing.
➤ Shown in the broken triangle and labeled “No Fire: When Any One Side Is Missing.”

Application in Safety
• Prevention Strategy: To prevent fires, remove or control at least one side of the
triangle.
Remove fuel (e.g., isolate flammables)

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 ○ Remove fuel (e.g., isolate flammables)
○ Limit oxygen (e.g., inert gas purging)
○ Eliminate ignition sources (e.g., grounding, explosion-proof equipment)

This graph from Chemical Process Safety illustrates the relationship between temperature,
vapor concentration, and flammability of a substance. It helps understand under what
conditions a vapor mixture is flammable or not — essential for fire and explosion prevention.

Key Axes
• X-axis (Temperature):
Increases from left to right. Important reference points:
○ Flash Point Temperature: Minimum temp where enough vapor is produced to
ignite in air (with external ignition).
○ Autoignition Temperature (AIT): Temp at which a substance ignites
spontaneously without any ignition source.
• Y-axis (Concentration of Flammable Vapor):
Represents the amount of flammable vapor in air.

Important Boundaries
1. Lower Flammability Limit (LFL):
○ Below this, the mixture is too lean (not enough fuel) → Not flammable.
2. Upper Flammability Limit (UFL):
○ Above this, the mixture is too rich (not enough oxygen) → Not flammable.
3. Saturation Vapor Pressure Curve:
○ Indicates how much vapor is in equilibrium with its liquid at a given temperature.

Regions Explained
• Not Flammable (Bottom-left):
Low temp + low vapor concentration = no fire risk.
• Flammable Region (Middle Zone):

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 • Flammable Region (Middle Zone):
Vapor concentration is between LFL and UFL → risk of ignition exists.
• Autoignition Region (Far-right bubble):
Even without a spark or flame, fire can occur if temperature is high enough and vapor is
in the flammable range.
• Mist Region:
Separate concern — mists can burn even if vapor concentration is below the LFL

• Fire and explosion properties of materials

This diagram illustrates the Cleveland Open-Cup (COC) method for determining the flash
point of a liquid, as described in Chemical Process Safety by Crowl & Louvar.

What is Flash Point?

The flash point is the lowest temperature at which a liquid emits enough vapor to ignite
momentarily when exposed to an ignition source.

How the Cleveland Open-Cup Test Works

This setup is designed to gradually heat a liquid sample in an open container and test for
vapor ignition:
Key Components:
• Open Cup with Liquid: Holds the sample being tested.
• Heating Plate: Heats the liquid to increase vapor concentration.
• Thermometer: Monitors the temperature of the liquid.
• Test Flame Applicator: A small flame that is moved back and forth across the cup to test
for ignition.
• Bunsen Burner: Heats the plate via gas from the gas supply.

Test Procedure:
1. Heat the liquid slowly using the heating plate.
2. Monitor the temperature with the thermometer.
3. Periodically pass the test flame over the cup surface (without touching the liquid).

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 3. Periodically pass the test flame over the cup surface (without touching the liquid).
4. When a visible flame briefly ignites over the surface, the thermometer reading is
recorded → this is the flash point.

• The “ cu ” h d exposes the vapor to air, so it usually shows a higher flash

point compared to “closed cup” methods.
• This method simulates real-world open conditions, such as fuel spills or open
containers.

This graph shows the maximum pressure (Pₘₐₓ) resulting from methane-air combustion in a
20-liter sphere, plotted against methane volume percentage in air. It helps visualize the
flammability limits and explosion behavior of methane.

Axes Explained
• X-axis (Methane Volume % in Air):
Shows the percentage of methane mixed with air.
• Y-axis (Pₘₐₓ in psia):
Indicates the maximum pressure reached during combustion.

Key Features of the Graph

1. LFL (Lower Flammability Limit):
Around 5% methane in air — combustion begins here. Below this, the mixture is too
lean (not enough fuel), so no ignition occurs.
2. UFL (Upper Flammability Limit):
Around 16% methane in air — combustion ceases beyond this point. Above this, the
mixture is too rich (not enough oxygen).
3. Flammable Range (Between LFL and UFL):
Within this range, the mixture can ignite and explode.
○ The maximum pressure is observed between 8–10% methane, which is
considered the stoichiometric or most efficient combustion mix.

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 considered the stoichiometric or most efficient combustion mix.

Experimental Data
• Two sets of experimental data are shown:
○ Mashuga and Crowl (●)
○ Kuchta (□)
These validate each other with slight variations, indicating reproducibility of the
data across studies.

Interpretation
• The curve is bell-shaped, peaking at the optimal air-fuel ratio where combustion is most
complete and violent (hence high pressure).
• Outside the LFL and UFL, no explosion occurs (pressure stays near zero).

This is a flammability diagram (or ternary diagram) for methane-air-inert gas mixtures, used
to visualize the combinations of fuel, oxygen, and inert gas (e.g., nitrogen) that result in a
flammable or non-flammable mixture.

Axes and Corners Explained

This triangle shows three components of a gas mixture:
• Left corner (Methane %)
The fuel. Increases from bottom to top.
• Right corner (Passive Agents %)
Typically inert gases like nitrogen. Increases from bottom-right to top.
• Bottom corner (Oxygen %)
The oxidizer. Increases from left to right.
Each point inside the triangle represents a unique combination of methane, oxygen, and inert
gas.

Important Features of the Diagram

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 Important Features of the Diagram
• Gray shaded area: The flammable region — where the mixture will burn if ignited.
• LFL (Lower Flammability Limit):
The minimum methane concentration needed for combustion to occur.
• UFL (Upper Flammability Limit):
The maximum methane concentration beyond which combustion won’t occur due to
lack of oxygen.
• Stoichiometric Line (red):
Represents the most chemically efficient ratio (ideal combustion condition).
• Air Line (blue):
Represents mixtures where the only components are methane and air (air = ~21%
oxygen, ~79% nitrogen). Moving along this line changes only the methane concentration
in air.

Key Insights
• Adding inert gas (e.g., nitrogen) shifts the mixture outside the flammable region,
making it safe — this is the basis of inerting in process safety.
• Flammability only occurs within specific methane–oxygen combinations. Too little fuel
(left of LFL) or too little oxygen (right of UFL) → no fire.

• Ignition
• Explosions

This diagram from Chemical Process Safety illustrates the difference between detonation and
deflagration, two types of combustion (explosion) phenomena in gases. It shows their gas
dynamics, including how pressure evolves over distance.

1. Detonation
• Definition: A detonation is a supersonic explosion.
• Key Characteristics:
○ The reaction front moves faster than the speed of sound.
○ A shock front is generated and travels at the same speed as the reaction front.
○ Both fronts move together.
• Pressure Graph (Top Right):

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 • Pressure Graph (Top Right):
○ Very sharp pressure spike (nearly vertical rise).
○ Reaches a high peak overpressure (e.g., ~15 atm).
○ Follows a sharp drop to ambient pressure.
• ✅ Extremely destructive due to high shock wave intensity.

2. Deflagration
• Definition: A deflagration is a subsonic explosion (slower combustion).
• Key Characteristics:
○ The reaction front moves slower than the speed of sound.
○ The pressure front moves independently at the speed of sound.
○ They are separated in space and time.
• Pressure Graph (Bottom Right):
○ Gradual pressure rise and fall.
○ Lower peak overpressure than detonation.
• Less iolent than detona on but s ll dangerous depending on con nement.
Key Differences Summarized
Feature Detonation Deflagration
Speed Supersonic Subsonic
Reaction + Pressure Move together (same speed) Move separately
Shock Front Present Absent
Pressure Rise Instantaneous (sharp peak) Gradual
Damage Potential Much higher Lower (but still harmful)

• Concepts to Prevent Fires and Explosions

• Inerting
• Static electricity
• Dust explosion
• Safety Procedures and Designs

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