This document discusses the fire triangle and explosive limits as they relate to hazardous areas. It uses a scenario of a leaking gas cylinder to demonstrate how the fire triangle of fuel, oxygen, and ignition can cause an explosion. Over time, the gas and air form an explosive mixture that occupies a larger space. A spark then ignites the mixture, causing an explosion throughout the area where the gas-air mixture was present. The key factors for the explosion were that the mixture was within the explosive limits, meaning it was at a proper, not too rich or too lean, concentration for detonation.

1. Through the study of :-
• Formation of Hazardous Area
• Ignition
• Upper & Lower Explosive Limits
• Prevention
WORKING OF A FIRE TRIANGLE
Consider…… an industrial facility with
A source of Flammable Gas or Vapors.
(Referred to as FUEL in this study)

2. OXYGEN
(From the surrounding Air)
FUEL
12.00

3. OXYGEN FUEL
OXYGEN is present in the air
12.00
Source of release .

4. OXYGEN FUEL
A mixture of flammable gas & oxygen starts
to form an explosive GAS-AIR MIXTURE
12.10

5. OXYGEN FUEL
12.20
The volume of the GAS-AIR Mixture
increases with time

6. OXYGEN FUEL
12.30
The GAS-Air mixture is explosive and is now
occupying the most of the space

7. OXYGEN FUEL
12.31
ANY spark can ignite this
AIR GAS MIXTURE.
This spark can be from a
number of sources.
IGNITION
The GAS-Air mixture is explosive and is now
occupying the most of the space

8. OXYGEN FUEL
12.31
ANY spark can now ignite
this AIR GAS MIXTURE.
This spark can be from a
number of sources.
IGNITION
The GAS-Air mixture is explosive and is now
occupying the most of the space near &
around the leaking GAS cylinder

9. OXYGEN FUEL
IGNITION
ANALYSIS
Before the explosion .
A mixture of flammable GAS & oxygen (from air) was being formed and gaining more
volume with passage of time .
But still there was no explosion because there was no SPARK to ignite the mixture.
With an accidently generated spark the MIXTURE was ignited and resulted in an
EXPLOSION.
The effects of the heat and flame covered the whole of the area previously occupied by the
GAS-AIR mixture .
AT this point , we will stop our clock and go , one
slide back to analyze the situation.

10. OXYGEN FUEL
IGNITION
We can easily recognize the EXPLOSIVE TRIANGLE present in this situation
and responsible for the explosion.
OXYGEN + FUEL + SPARK

11. OXYGEN FUEL
IGNITION
The Explosive Triangle resulted in an explosion due to the following favorable
condition :
The GAS-AIR mixture was in proper proportion (NOT RICH & NOT LEAN)
Technically the Mixture composition was within the EXPLOSIVE LIMITS.

12. OXYGEN FUEL
12.30
High concentration of air and
very low concentration of
FUEL in this region so there
will be no explosion even
with a spark .
Explosive Triangle will simply
not exist.
The mixture is too thin or
lean.
This is the START of the
LOWER EXPLOSIVE LIMIT
High concentration of FUEL
and very low concentration of
AIR in this region so there
will be no explosion even
with a spark .
Explosive Triangle will not
exist.
The mixture is too rich.
This the START of the
UPPER EXPLOSIVE
LIMIT
ThemostfavorableconcentrationofAIR–FUELMixture

13. OXYGEN FUEL
12.30
This
concentration of
the GAS-AIR
Mixture is most
dangerous and
may explode if
ignited

14. MOST EFFECTIVE BASIC RULE OF PREVENTION/ SAFETY in HAZARDOUS AREAS
STOP / Prevent the formation of FIRE TRIANGLES
Guide lines : IEC 60079