Introduction to Process Safety

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Introduction to Process Safety
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To know is to survive and to ignore fundamentals
is to court disaster

• H.H. Fawcett and W.S. Wood, Safety and
  Accident Prevention in chemical operation, New
  York, Wiley, 1984.

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Three important terminologies

• Safety or loss prevention the prevention of
  accident through the use of appropriate
  technologies to identify the hazards of a
  chemical plant and eliminate them before accident
  occurs
• Hazard a chemical or physical condition that
  has the potential to cause damage to people,
  property or the environment
• Risk a measure of human injury, environmental
  damage or economic loss in terms of both the
  incident likelihood and the magnitude of the loss
  or injury

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Definition of Risk

• Risk Severity x Likelihood

• Extent of Damage
• Probability of Fatality
• Monetory Losses

• Likelihood of failure

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Risk is expressed in as Rating

• Rating is typically
• simple to use and understand
• Not require extensive knowledge to use
• Have consistent likelihood ranges that cover the
  full spectrum of potential scenarios
• In applying risk assessment
• Clear guidance on applicability is provided
• Detailed descriptions of the consequences of
  concern for each consequence range should be
  described
• Have clearly defined tolerable and intolerable
  risk levels
• Following risk assessment
• Scenarios that are at an intolerable risk level
  can be mitigated to a tolerable risk level on the
  matrix
• Clear guidance on what action is necessary to
  mitigate scenarios with intolerable risk levels
  are provided

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Example of a Consequence Range
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Example of Likelihood Ranges
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Example Risk Ranking Categories
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Risk Matrix
Risk Probability of occurrence x Consequence of
occurrence
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Guidelines for Risk Mitigation
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Accident and Loss Statistics

• Accident and loss statistics are used to measure
  the effectiveness of safety programs.
• Among statistical methods used to characterize
  accident and loss performance
• - OSHA (Occupational Safety and Health
  Administration, USA) incidence rate
• - Fatal accident rate (FAR)
• - Fatality rate or deaths per person per year
• These methods report number of accidents and/or
  fatalities for fixed number of workers during
  specified period.

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OSHA Incidence Rate

• based on cases per 100 worker years.
• 1 worker year 50 work weeks/yr x 40 hrs/weeks
  2000 hrs
• based on 200,000 hrs worker exposure to hazard
• two types of calculation (1) based on injuries
  and illness (2) based on lost workdays
• OSHA (1) number of injuries illness x
  200,000 / total hrs work by all employees during
  period covered
• OSHA (2) number of lost workdays x 200,000 /
  total hrs work by all employees during period
  covered

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Fatality Accident Rate

• Used by British chemical industries. Data is
  widely available in literature.
• Fatalities based on 1000 employees working their
  lifetime. Employees assumed working total 50
  years (108 working hrs).
• FAR number fatalities x 108 / total working hrs
  by all employees during period covered
• Fatality rate number of fatalities per year /
  total number of people in applicable population
• FAR can be converted to fatality rate (or vice
  versa) if number of exposed hours is known.
• OSHA incidence rate cannot be converted to FAR or
  fatality rate because it contains both injury
  fatality information.

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Example

• Given FAR 2. If employee works 8 hr shift 300
  days per year, compute fatality rate
• Fatality rate 8 hrs/day x 300 days/year x 2
  deaths/108 hrs 4.8 x 10-5 death per person per
  year
• More rock climbers are killed travelling by car
  than are killed during rock climbing. Is this
  statement supported by statistics?
• From data, travelling by car, FAR57, rock
  climbing, FAR 4000.
• Rock climbing produces more fatalities per
  exposed hrs but spend more time(exposed hrs)
  travelling by car. Think about this...

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Example
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Tolerable Risk

• Risk cannot be eliminated entirely.
• Every chemical process has a certain amount of
  risk associated with it.
• At some point in the design stage someone needs
  to decide if the risks are tolerable".
• Each country has it owns tolerability criteria.
• One tolerability criteria in the UK is "as low as
  reasonable practicable" (ALARP) concept
  formalized in 1974 by United Kingdom Health and
  Safety at Work Act.
• Details will be treated later (TopicQRA)

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In life, there is always some risks

• There is no such thing as zero risk
• All activities involve some risks
• The issue is at level should we tolerate these
  risks

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Tolerability Criteria

• This framework is represented as a three-tier
  system as shown in figure. It consists of several
  elements
• (1) Upper-bound on individual (and possibly,
  societal) risk levels, beyond which risks
  unacceptable.
• (2) Lower-bound on individual (and possibly,
  societal) risk levels, below which risks are
  deemed not to warrant regulatory concern.
• (3) intermediate region between (1) and (2)
  above, where further individual and societal risk
  reductions are required to achieve a level deemed
  "as low as reasonably practicable (ALARP)".

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ALARP Criteria
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Causes of Accidents and Incidents

• Incidents and Accidents are caused by either
  unsafe behaviours (substandard practice) and/or
  unsafe conditions (substandard designs).

Unsafe behaviours are handled by Occupational
Safety Program, Unsafe conditions are managed
through Process Safety Programs.
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Inherent Safety
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Inherent Safety

• To make the concept more understandable, the
  following four words have been recommended to
  describe inherent safety
• Minimise (intensification)
• Substitute (substitution)
• Moderate (attenuation and limitation of effects)
• Simplify (simplification and error tolerance)

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Minimise (example)

• Change from larger batch reactor to smaller
  continuous reactor
• Reduce storage inventory of raw materials
• Improve control to reduce inventory of hazardous
  intermediate chemicals
• Reduce process hold-up

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Substitute (example)

• Use mechanical pump seals vs packing
• Use welded pipe vs flanged
• Use solvent that are less toxic
• Use mechanical gauges vs mercury
• Use chemicals with higher flash point, boiling
  points, and other less hazardous properties
• Use water as heat transfer fluid instead of hot
  oil

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Moderate (example)

• Use vacuum to reduce boiling point
• Reduce process temperature and pressure
• Refrigerate storage vessel
• Dissolve hazardous materials in safe solvent
• Place control rooms away from operation
• Operate at conditions where runaway reactions are
  not possible
• Separate pump rooms from other rooms
• Barricade control rooms and tanks

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Simplify (example)

• Keep piping systems neat and visually easy to
  follow
• Design control panels that are easy to comprehend
• Design plants for easy and safe maintenance
• Pick equipment with low failure rates
• Separate systems and controls into blocks that
  are easy to comprehend and understand
• Label pipes for easy walking the line
• Label vessels and controls to enhance
  understanding
• Add fire and explosion resistant barricades

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Inherent Safety Concept

• Reduce the risk at early stage of design

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PROJECT PHASE
Safety issues must be embedded within all project
life-cycle
Relationship of six-stage process study system to
project life-cycle
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Many hazard identification technique can be used
at appropriate cycle
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Hazard identification technique and project phase
Method used Project life cycle stage Project life cycle stage Project life cycle stage Project life cycle stage Project life cycle stage Project life cycle stage Project life cycle stage Project life cycle stage
Method used 0 1 2 3 4 5 6 7
Checklist X X X X X X X X
RR X X (X) (X)
What-If X X X X
FTA X X X (X) X
ETA X X X (X) X
FMEA (X) X X (X)
LOPA X X X
HAZOP (X) X X
PHR X (X)