C2 - Fire And Explosion Flashcards
Flash point
The lowest temperature of a liquid at which sufficient vapour is given off to momentarily ignite (flash), when an external ignition is applied
Fire point
The lowest temperature of a liquid at which sufficient vapour is given off at the surface that the application of an external ignition source will lead to continual burning
Auto ignition
The lowest temperature at which a substance will ignite without the application of an external ignition source.
Limits of flammability
LEL = Lower explosive limit
UEL = Upper explosive limit
Flammable range = spread between the LEL and UEL
Explosion
A sudden and violent release of energy, causing a blast wave.
Deflagration vs Detonation
Detonation = reaction/ pressure wave (shockwave)propagates at supersonic speeds and is very destructive (less common) - explosive force
Deflagration = reaction/ pressure wave propagates at subsonic speeds <10m/s and is less destructive but more common. Rapid burning of combustible fuels
UVCE
CVCE
BLEVE
UVCE = Unconfined vapour cloud explosion (Flixbourough)
CVCE = Confined vapour cloud explosion (Hickson and Welch)
BLEVE = Boiling liquid expanding vapour explosion (Mexico city)
Control measures to prevent and mitigate explosions - VICES
V= ventilation - ensure vapours given off are rapidly dispersed I= Ignition - Remove ignition sources from area C= Containment - Prevent escape of flammable materials E= Exchange - for a less flammable option S= Separation - limit amount of flammable substances by segregation
Principle controls to reduce vapour explosions
- Structural protection to reduce effects of explosion
- Plant, process design and control to reduce vapours coming into contact with ignition
- Limit amount of materials
- Prevent release of vapours
- Segregation and storage ie stored outside
- DSEAR zoning
- Inerting
- Explosion relief panels
- Control/ limit ignition sources
- Sensing vapour LEL up
Mechanism of dust explosions
- Combustible solid particle size
- Dispersal into air to form mixture
- Explosive concentration LEL
- Ignition of suitable energy
Building Factors that influence the spread of fire
- Distance from source of fire
- Materials used in the building construction
- Layout of the building
- Materials used as decoration and furnishings
- Use of fire compartment design
- Location of air in ventilation / free flowing air
- location and provision of fire shutters
DSEAR zones
0-2. = Gas/ vapours 20-22 = Dusts
0/20 = continuously or for long periods of time or frequently 1/21 = Likely to occur in normal operation occasionally 2/22 = not likely to occur in normal operation but if it does occur will be for short duration
Items to be included in fire safety training
- Fire triangle
- Fire prevention such as storage of flammable materials
- Good house keeping
- Actions to take in event of a fire
- Procedures for evacuation, calling em services
- Locations of fire fighting equipment and their use
- Additional training for resp persons
- Assembly points
- liaison with em services
- Evacuating disability employees
What is the purpose of DSEAR zone classification
The purpose of the DSEAR zone classification is to ensure that only suitably designed electrical equipment and protective systems are used in areas where a flammable atmosphere may arise.
General headings to cover during a fire risk assessment
- Fuels
- Ignition sources
- People issues - number of people, locations, contractors
- Preventative actions - compartmentalisation, sprinklers
- Mitigating actions - fire fighting equipment and locations
- Means of escape -
- Management systems - testing, drills, training
Factors to consider when designing a sprinkler system
- Availability of water supply
- Coverage of area being considered
- Type of head
- location of water tank and pump
- Interlink with fire alarm
- type of pump (diesel, electric)
- Spray patterns
- coverage and flammability of materials
- in rack heads
- need for fire water run off control
What is the hierarchy of control required by DSEAR
- Avoid\ minimise releases
- Control release at source
- Prevent formation of explosive atmosphere
- Ensure any release is collected, contained and removed
- Avoid ignition sources
- Avoid adverse conditions
- Segregation of incompatible substances
Difference between Active and passive systems designed to protect against dust explosions
Active - live system that reacts to an explosion (pressure rise) and produces a counter acting effect ie release a suppressant
Passive - a static system which relieves pressure by providing a controlled escape route for the explosive pressure ie explosion panel
Principles to prevent or minimise effects of dust explosions
- Eliminate ignition sources
- Limit dust cloud generation
- Minimise harm by controlling the explosion
