Assessment of Plant Disaster Risk 

Major risks possibly occurred in hazardous material handling plant are three kinds of disaster listed below.
In assessments of plant disaster risks, firstly, initial events of these disasters are identified and then the frequency and the severity of the disaster from each initial event is decided.
Finally, the risk level for each initial event is calculated with the frequency and severity of the disaster, and it is used when deciding the urgency and necessity of countermeasures.

  1. Spill Hazard and gas dispersion
    • Leakage
    • Liquid spreading
    • Evaporation  
    • personal suffering by gas dispersion
  2. Explosion
    • VCE (Vapor Cloud Explosion); to yield extremely high pressure wave to cause damage. Explosion of vapor cloud in outdoor.
    • Flash Fire; not to yield pressure wave, but yield high temperature atmosphere by extremely high burning speed to damage on a human life.
    • BLEVE (Boiling Liquid Expanding Vapor Explosion); Explosion phenomena by explosive boiling of the contained liquid caused from rapture of the vessel.
    • Fireball; When huge amount of flammable gas is released to atmosphere (after BLEVE, for example) and ignited, flammable gas is burned rapidly to yield fireball, which release the intensive heat wave to the surrounding area.
  3. Fire
    • Damage from heat radiation
    • Boil over

 

　Assessment  Procedures　

  1. Initial Event
    Leakage is considered as an initial event in assessment of plant disaster risk, because initial event to trigger to plant disasters is leakage in most of case.
    If the leakage is caused from human error or equipment failure, then those will be considered as initial event.
    In case of cable fire in electrical room, building fire by stroke of lightning etc,. the fire itself will be the initial event.
    It is very important how to decide the initial event, which requires deep knowledge and experience of the plant. We, FPEC has enough knowledge and experience to propose appropriate way.

  2. Assessment of likelihood of disaster
    In this assessment, the event tree shall be prepared for each initial event and probabilities of human error or equipment failure shall be applied to calculate the likelihood, that is, frequency of the disaster (times/year). 
    For the above study, layout drawings of the plant, P&ID flow diagrams, equipment data sheets etc, are required. Statics data on probabilities of human error or equipment failure will be obtained from Guidance for risk assessment by Government of Japan, Nuclear Power Plant related data, or other published data in USA/EU.
    We can evaluate the relative likelihood index based on the maximum likelihood of the disaster when deciding priority relatively.

  3. Assessment of severity of disaster
    There are a lot of indicators to assess damage from disaster (severity), such as damage on human body, cost required for rebuilding of damaged facilities, loss caused from interruption of business, harmful rumors, or combination of them. Which indicator is prioritized is based on the customer's safety policy and philosophy, so it will be determined in consultation with the customer.
    Then, we set severity categories for each indicator. The severity of the disaster is determine based on the corresponding category.
    When setting the categories, we will refer to Guidance for risk assessment by Government of Japan, Nuclear Power Plant related data, or other published data in USA/EU.
    We can evaluate the relative severity index based on the maximum severity of the disaster in the same way of the relative likelihood index, when deciding priority relatively.
    Furthermore, when estimation of loss caused from the disaster is needed, we can provide disaster preventing simulations by the software developed by FPEC, refer to Plant Disaster Preventing Simulation.

  4. Assessment of  risk level of  plant disaster
    The risk level (R) for each initial event is calculated with the likelihood (R), and the severity (S) calculated above in accordance with the formula below.
    　　　　R　=　F  x  S
    According to the risk level (R), risk assessment will be classified as the example below.

    Risk Assessment 

    Risk Level（R)＝F x S

    Remarks

    From

    To

    EXTREME Risk

    1.00E-03

    ～

    Risk reduction measure is urgently required.

    HIGH Risk

    1.00E-04

    <1.00E-03

    Risk reduction measure is required as soon as possible.

    MODERATE Risk

    1.00E-05

    <1.00E-04

    There is no urgency, but risk reduction measure is hopefully required.

    LOW Risk

    ～

    <1.00E-05

    Especially risk measures need not be taken, but safety management is implemented