Loss of Containment

The CCPS Guidelines for Chemical Process Quantitative Risk Analysis includes an appendix which lists Loss of Containment (LoC) causes in the Chemical industry i.e. where the plant inventory is discharged to the environment.

Incidents are grouped according to the following types of loss (click the icons below):

DISCHARGE
DEGRADATION
DAMAGE
DEVIATION

This does not presume to be an exhaustive list but covers the following potential causes:

  • CONTAINMENT LOST VIA AN “OPEN-END” ROUTE TO ATMOSPHERE [DISCHARGE]
    1. Due to genuine process relief or dumping requirements
    2. Due to maloperation of equipment in service, e.g., spurious relief valve operation or rupture disk failure, etc.
    3. Due to operator error, e.g., drain or vent valve left open, misrouting of materials, tank overfilled, unit opened up under pressure, etc.
  • CONTAINMENT FAILURE UNDER DESIGN OPERATING CONDITIONS DUE TO IMPERFECTIONS IN THE EQUIPMENT [DEGRADATION]
    1. Imperfections arising prior to commissioning and not detected before start-up (due to poor inspection or testing procedures)
      • Equipment inadequately designed for proposed duty, e.g., wrong materials specified, pressure ratings of vessel or pipework inadequate, temperature ratings inadequate, etc.
      • Defects arising during manufacture, e.g., wrong materials used, poor workmanship, poor quality control, etc.
      • Equipment damage or deterioration in transit or during storage.
      • Defects arising during construction, e.g., welding defects, misalignment, wrong gaskets fitted, etc
    2. Imperfections due to equipment deterioration in service and not detected before the effect becomes significant (due to inadequate monitoring procedures in those cases where deterioration is gradual)
      • Normal wear and tear on pump or agitator seals, valve packing, flange gaskets, etc.
      • Internal and/or external corrosion, including stress corrosion cracking.
      • Erosion or thinning.
      • Metal fatigue or vibration effects.
      • Previous periods of gross maloperation, e.g., furnace operation at above the design tube skin temperature (“creep”).
      • Hydrogen embrittlement.
    3. Imperfections arising from routine maintenance or minor modifications not carried out correctly, e.g., poor workmanship, wrong materials, etc.
  • CONTAINMENT FAILURE UNDER DESIGN OPERATING CONDITIONS DUE TO EXTERNAL AGENCIES [DAMAGE]
    1. Impact damage, such as by cranes, road vehicles, excavators, machinery associated with the process, etc.
    2. Damage by confined explosions due to accumulation and ignition of flammable mixtures arising from small process leaks, e.g., flammable gas build-up in analyzer houses, in enclosed drains, around submerged tanks, etc.
    3. Settlement of structural supports due to geological or climatic factors or failure of structural supports due to corrosion, etc.
    4. Damage to tank trucks, rail cars, containers, etc., during transport of materials on- or off-site.
    5. Fire exposure.
    6. Blast effects from a nearby explosion (unconfined vapor cloud explosion, bursting vessel, etc.), such as blast overpressure, projectiles, structural damage, etc.
    7. Natural events (acts of God) such as windstorms, earthquakes, floods, lightning, etc.
  • CONTAINMENT FAILURE DUE TO DEVIATIONS IN PLANT CONDITIONS BEYOND THE DESIGN LIMITS [DEVIATION]
    1. Overpressuring of equipment
      • Due to a connected pressure source
        1. gas pressure source
          • gas breakthrough into downstream low-pressure equipment due to failure of a pressure or level controller, isolation valve opened in error, etc.
          • pressurized backflow into low-pressure equipment, e.g., due to compressor failure
        2. liquid pressure source
          • pumping up of blocked-in gas spaces
          • hydraulic overpressuring due to a block-in condition downstream
          • excessive surge or hammer, such as by sudden valve closure on liquid transfer line
      • Due to rising process temperature
        1. loss of cooling
          • loss of coolant flow, e.g., to a reactor cooler, to a distillation column condenser, etc.
          • elevated coolant temperature, e.g., loss of cooling water fans, etc.
          • fouling of coolers, condensers, or exchangers
        2. excessive heat input (thermal)
          • heater control faults, such as on steam or hot oil heated systems
          • ingress of hot extraneous materials, e.g., slop-over
        3. excessive heat generation (chemical)
          • reactor runaway, e.g., due to loss of reaction diluent, high feed rate, high molar ratio, accumulation of unreacted reactants due to inadequate mixing or temporary loss of reaction subsequently leading to a runaway, etc.
          • exotherming due to ingress of catalytic impurities, e.g., backflow from ethylene oxide consumer unit into feed tank.
          • exotherming due to mixing of incompatible chemicals, e.g., H2SO4 with NaOH
          • exothermic decomposition of thermally unstable or explosive material such as peroxides, e.g., due to temperature rise, overconcentration, or deposition on hot surfaces
      • Due to an internal explosion arising from formation and ignition of flammable gas mixtures, mists, or dusts
        1. ingress of air, e.g., due to inadequate purging of equipment at plant start-up, due to loss of nitrogen purge on flare headers, storage tanks, centrifuge systems, dryers, etc.
        2. loss of critical inert diluent, e.g., loss of nitrogen padding on an ethylene oxide storage tank, loss of nitrogen to the make-up section of a nitrogen/air solids conveying system
        3. failure of explosion suppressants
        4. flammable excursion in oxidation processes, e.g., due to high air or oxygen rates, or loss of conversion
      • Due to physically or mechanically induced forces or stresses
        1. expansion upon change of state, e.g., freezing of water in pipe runs
        2. thermal expansion of blocked-in liquids, e.g., in heat exchangers or long pipe runs
        3. ingress of extraneous phases, e.g., gas compressor failure due to liquid carry-through to machine suction, condensate hammer in steam lines, etc.
    2. Underpressuring of equipment (for equipment not capable of withstanding vacuum)
      • By direct connection to an ejector set or to equipment normally running under vacuum
        1. due to equipment malfunction, e.g., loss of liquid seal due to failure of a level controller causing vacuum to be applied upstream, etc.
        2. due to operator error, e.g., isolation valve left open, etc.
      • Due to the movement or transfer of liquids
        1. pumping out of tanks or vessels
        2. emptying or draining elevated blocked-in equipment under gravity
      • Due to cooling of gases or vapors
        1. condensation of condensable vapors, e.g., vessel blocked-in after steaming
        2. cooling of noncondensable gases or vapors, e.g., storage tank by heavy from rainfall in summer
      • Due to solubility effects, e.g., dissolution of gases in liquids
    3. High metal temperature (causing loss of strength)
      • Fire under equipment, e.g., due to spillage, pump leak, etc.
      • Flame impingement causing local overheating, e.g., on furnaces due to misalignment or maladjustment of burners
      • Overheating by electric heaters, e.g., due to failure of high temperature cutout
      • Inadequate flow of fluid via heated equipment, e.g., furnace tube failure on loss of hot oil flow
      • Higher flow rate or higher temperature of the hotter stream, or lower flow rate or higher temperature of the colder stream, via a heat exchanger
    4. Low metal temperature (causing cold embrittlement and overstressing)
      • Overcooling by refrigeration units, e.g., due to control faults, wrong refrigerant, etc
      • Incomplete vaporization and/or inadequate heating of refrigerated material before transfer into equipment of inadequate temperature rating, e.g., due to control faults on a liquid ethylene vaporization unit
      • Loss of system pressure on units handling liquids of low boiling point
    5. Wrong process materials or abnormal impurities (causing accelerated corrosion, chemical attack of seals or gaskets, stress corrosion cracking, embrittlement, etc.)
      • Variations in stream compositions outside design limits
      • Abnormal impurities introduced with raw materiaIs or wrong raw materials
      • By-products of abnormal chemical reactions
      • Oxygen, chlorides, or other impurities remaining in equipment at start-up due to inadequate evacuation or decontamination
      • Impurities entering process from atmosphere, service connections, tube leaks, etc., during operation.

The UK Health & Safety Executive also analysed Loss of Containment incidents and their findings are published in research report HSL/2003/07

X