W6- O&G Safety Flashcards
Major hazards
Fire and explosion from ignition of HC releases (HCR)
Loss of stability
Structural filure
Hazard
Potential for human injury, damage to environment
Risk
Combination of chance of hazardous event will occur and severity of consequences
Frequency (likelihood) x consequence (effect on personnel)
Assessed by risk matrix, layers of protection analysis (LOPA)
Tolerability of risk
Unacceptable
Aas low as reasonably possible (ALARP)
Broadly acceptable regions
Basis for tolerability
COmparative
Cost/benefit
Technology (ALARA)
Presumption of danger
Broad major offshore hazards
HC Hazards: Process, risers, wells
Non-HC Hazards: non-process fires, helicopter, structural failure, impacts, ship collisions
Fire
Result of sequence of exothermic chain reactions between fuel, heat and oxidising agent (O2)
Redox process involving rapid oxidation of fuel source at elevated temperatures, accompanied by release of energy and production of heat, light, gaseous by-products
Fire types:
Jet Fire: combustion of fuel continuously released with significant directional momentum
Pool fire: turbulent diffusion fire burning above horizontal pool of vaporising HC fuel, where fuel has low initial momentum (confined & unconfined pool fires)
Flash fire: fire propogating at low speed through gas cloud
Fire ball: spherical fire resulting from immediate ignition of large inventory of gas
Explosion & types
Rapid increase in volume with concurrent violent release of thermal energy
Energy from chemical potential to mechanical to surroundings;
Generates high temp & release of gas to atmosphere
Types: nuclear, chemical, physical (BLEVE)
Flammability/explosivity limits
Lower flammable/explosive limit (LFl/LEL):
Below this conc., a vapour in the air is too lean to burn even with an ignition source present
Upper flammable/explosive limit (LFl/LEL):
Highest conc in the air for which vapours can burn (above it vapour is too rich to burn)
Vapour cloud explosion (VCEs)
Result of HC release into atmosphere (unconfined/confined VCE)
Cloud may immediately ignite or dispersion phase for time
Deflagration
Combustion which proceeds from reaction zone to unreacted zone via HMT only- fast burning fire
High propagation speed- flame accelerates (deflagration) & requires generation mechanism or cloud ignited strongly
Detonation
Energy from reaction to unreacted zone with reactive shock wave- supersonic shockeave velocity
Major HC accident events
Frequency: leak location, volume, rate; effect on blowdown system; reliability of protective systems
Consequences: gas dispersion; jet/pool fires; smooke; escalation to adjacent structures
Inherently safer systems
Separation
Integration of design & safety
Substitution
Simplification
Stability
Recovery
