Lecture 5. Process safety inherent safetypdf

Process safety

1. Ir. Dr. TeowYeitHaan
INHERENT SAFETY

2. Layer of Process Safety
Inherent Passive Active Procedural
•Ideally this means
eliminating the
hazard from the
design
•Building the protection
into the design so it
cannot be easily
changed
•Reduce frequency
and/or consequence
of hazard
•e.g. design conditions
should mean that
process cannot move
outside of the safe
envelope under any
circumstances
•Intended to prevent,
control or mitigate a
potentially hazardous
scenario. e.g.
•Prevent: high level trip
isolates flow into a tank
before it can overfill
and lose containment
•Control: a restrictive
orifice plate limits the
rate of loss of
containment if a line
fails
•Mitigate: heat
activated links open
deluge valves to spray
water in case of fire
•Systems which are
intended to manage risk
•Safety/process
management system
(SMS)/(PMS)
✓Company policy
✓Site rules
✓Operating procedures
✓Training / refresher
training
✓Maintenance and
inspection regimes
✓Test procedures and
schedules
✓Emergency response
plans (on-and off-site)

3. Layer of Process Safety
Inherent Passive Active Procedural
•Ideally this means
eliminating the
hazard from the
design
•Building the protection
into the design so it
cannot be easily
changed
•Reduce frequency
and/or consequence
of hazard
•e.g. design conditions
should mean that
process cannot move
outside of the safe
envelope under any
circumstances
•Intended to prevent,
control or mitigate a
potentially hazardous
scenario. e.g.
•Prevent: high level trip
isolates flow into a tank
before it can overfill
and lose containment
•Control: a restrictive
orifice plate limits the
rate of loss of
containment if a line
fails
•Mitigate: heat
activated links open
deluge valves to spray
water in case of fire
•Systems which are
intended to manage risk
•Safety/process
management system
(SMS)/(PMS)
✓Company policy
✓Site rules
✓Operating procedures
✓Training / refresher
training
✓Maintenance and
inspection regimes
✓Test procedures and
schedules
✓Emergency response
plans (on-and off-site)

4. Layer of Process Safety
Inherent Passive Active Procedural
•Ideally this means
eliminating the
hazard from the
design
•Building the protection
into the design so it
cannot be easily
changed
•Reduce frequency
and/or consequence
of hazard
•e.g. design conditions
should mean that
process cannot move
outside of the safe
envelope under any
circumstances
•Intended to prevent,
control or mitigate a
potentially hazardous
scenario. e.g.
•Prevent: high level trip
isolates flow into a tank
before it can overfill
and lose containment
•Control: a restrictive
orifice plate limits the
rate of loss of
containment if a line
fails
•Mitigate: heat
activated links open
deluge valves to spray
water in case of fire
•Systems which are
intended to manage risk
•Safety/process
management system
(SMS)/(PMS)
✓Company policy
✓Site rules
✓Operating procedures
✓Training / refresher
training
✓Maintenance and
inspection regimes
✓Test procedures and
schedules
✓Emergency response
plans (on-and off-site)

5. Layer of Process Safety
Inherent Passive Active Procedural
•Ideally this means
eliminating the
hazard from the
design
•Building the protection
into the design so it
cannot be easily
changed
•Reduce frequency
and/or consequence
of hazard
•e.g. design conditions
should mean that
process cannot move
outside of the safe
envelope under any
circumstances
•Intended to prevent,
control or mitigate a
potentially hazardous
scenario. e.g.
•Prevent: high level trip
isolates flow into a tank
before it can overfill
and lose containment
•Control: a restrictive
orifice plate limits the
rate of loss of
containment if a line
fails
•Mitigate: heat
activated links open
deluge valves to spray
water in case of fire
•Systems which are
intended to manage risk
•Safety/process
management system
(SMS)/(PMS)
✓Company policy
✓Site rules
✓Operating procedures
✓Training / refresher
training
✓Maintenance and
inspection regimes
✓Test procedures and
schedules
✓Emergency response
plans (on-and off-site)

6. Layer of Process Safety
Inherent Passive Active Procedural
•Ideally this means
eliminating the
hazard from the
design
•Building the protection
into the design so it
cannot be easily
changed
•Reduce frequency
and/or consequence
of hazard
•e.g. design conditions
should mean that
process cannot move
outside of the safe
envelope under any
circumstances
•Intended to prevent,
control or mitigate a
potentially hazardous
scenario. e.g.
•Prevent: high level trip
isolates flow into a tank
before it can overfill
and lose containment
•Control: a restrictive
orifice plate limits the
rate of loss of
containment if a line
fails
•Mitigate: heat
activated links open
deluge valves to spray
water in case of fire
•Systems which are
intended to manage risk
•Safety/process
management system
(SMS)/(PMS)
✓Company policy
✓Site rules
✓Operating procedures
✓Training / refresher
training
✓Maintenance and
inspection regimes
✓Test procedures and
schedules
✓Emergency response
plans (on-and off-site)

7. Inherent
“ An inherently safer design is one that avoids hazards
instead of controlling them, particularly by reducing
the amount of hazardous material and the number
of hazardous operations in the plant.”
Example
➢Substituting water for a flammable solvent (latex paint
compared to oil base paint).

8. Passive
“ A passive safety refer to the process/equipment
design features that minimize frequency or
consequence of hazard without active functioning of
any device.”
Example
➢Containment dike around a hazardous
material storage tank.

9. Active
“ An active safety systems are systems activated in
response to a safety problem or abnormal event.”
Controls, safety interlocks, automatic shut down systems.
Multiple active elements
➢Sensor - detect hazardous condition
➢Logic device - decide what to do
➢Control element - implement action
Example
➢High level alarm in a tank shuts automatic feed valve.

10. Procedural
Standard operating procedures (SOP), safety rules and
standard procedures, emergency response procedures,
training.
Example
➢Confined space entry procedures

11. Example – Batch Chemical Reactor
Maximum adiabatic pressure for reaction determined to be
150 psig.
Hazard of concern
➢Runaway reaction causing high temperature and pressure and potential
reactor rupture
Passive
➢Run reaction in a 250 psig design reactor
➢Hazard (pressure) still exists, but passively contained by the pressure
vessel
Active
➢Use high temperature and pressure interlocks to stop feed and apply
emergency cooling
➢Provide emergency relief system

12. 12/63
Procedural
➢Train operator to observe temperature, stop feeds and apply cooling if
temperature exceeds critical operating limit
Inherent
➢Develop chemistry which is not exothermic, or mildly exothermic

13. Which strategy should we use?
13/63
Generally, in order of robustness and reliability:
But - there is a place and need for ALL of these strategies in a
complete safety program.
Inherent Passive Active Procedural
maintenance

14. Inherent Safety
Introduce in the late 1970's by Trevor Kletz.
Inherently safer plants are tolerant of operator errors,
abnormal conditions and often the most cost effective.
Although process/plant can be modified to increase inherent
safety at any time in its life cycle, the potential for major
improvement is the greatest at the earliest stage of process
development.
“An inherently safe plant relies on chemistry and physics to
prevent accidents rather than on control systems, interlocks,
redundancy, and special operating procedures to prevent
accidents.”

15. Opportunity for Safety Enhancement

16. Principles of Inherent Safety
Inherent safety principles (Kletz 1998)
➢ Minimization (Intensification)
➢ Substitute (Substitution)
➢ Moderation (Attenuation and limitation of effects)
➢ Simplification

17. Type Typical Techniques
Minimize
(Intensification)
Change from large 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
Principles of Inherent Safety
➢Minimize inventory of hazardous materials in process and
storage.
➢Minimized consequence of hazard realization.

18. Type Typical Techniques
Substitute
(Substitution)
Use solvents that are less toxic
Use chemicals with higher flash points, boiling
points, and other less hazardous properties
Use water as a heat transfer fluid instead of
hot oil
Use mechanical pump seals vs packing
Use welded pipe vs flanged
Use mechanical gauge vs mercury
➢Substitute with less hazardous material.

19. Type Typical Techniques
Moderate
(Attenuation and
limitation of effects)
Reduce process temperature and pressure
Dissolve hazardous material in safe solvent
Operate at conditions where reactor runaway
is not possible
Use vacuum to reduce boiling point
Refrigerate storage vessels
Place control rooms away from operations
Separate pump rooms from other rooms
Acoustically insulate noisy lines and equipment
Barricade control rooms and tanks
➢Less hazardous operating conditions/forms.

20. Type Typical Techniques
Simplify
(Simplification and
error tolerance)
Keep piping systems neat and visually easy to
follow
Pick equipment that requires less
maintenance/low failure rates
Design control panels that are easy to
comprehend
Design plants for easy and safe maintenance
Lebal vessels and controls to enhance
understanding
Separate systems and controls into blocks that
are easy to comprehend and understand

21. Why Safer Plants Are Cheaper?
FeaturesEffects of cost
saving
Reason
Minization large
Smaller equipments and less need
add-on safety equipment
SubstitutionModerateless need add-on safety equipment
Moderation moderate
less needs add-on safety
equipment
Simplificationlarge Less equipment
Source: (Kletz, 1999)

22. Tools for Inherent Safety
How to determine which process scheme is inherently safer
Tools that have been developed
➢Inherent Safety Index (ISI)
➢Prototype Index of Inherent Safety (PIIS)
➢Inherent Risk Assessment (IRA)
➢Integrated Risk Estimation Tool (IRET)

23. Inherent Safety Index (ISI)
The total index covers material (chemical) and process
PICITI III +=
Total
Index
Chemical
Subindex
Process
Subindex
Chemical sub-index
Process sub-index
Lower I
TI – inherently safer
max,CORImax)TOXIEXIFLI(max,INTImax,RSImax,RMICII ++++++=
max,max,max,max, STEQPTIPI IIIIII ++++=
(materialpart
(processpart)

24. Total Safety Index (I
TI)
Chemical Inherent Safety Index (I
CI) Process Inherent Safety Index (I
PI)
(a) Subindices for reaction hazard (a) Subindices for process conditions
Item symbolvalue Item SymbolValue
Heat of main reactionI
RM 0 – 4 Inventory I
I 0 - 5
Heat of side reactionI
RS 0 - 4 Process TemperatureI
T 0 - 4
Chemical InteractionI
INT0 - 4 Process Pressure I
P 0 - 4
(b) Subindices for hazardous materials (b) Subindices for process system
Flammability I
FL 0 - 4 Equipment I
EQ
Explosiveness I
EX 0 - 4 ISBL 0 - 4
Toxicity I
TOX 0 - 6 OSBL 0 - 3
Corrosivity I
COR 0 - 2 Process structureI
ST 0 - 5

25. Table 1: determination of heat reaction subindices I
RM & I
RS,
Heat of reaction / total reaction mass Score
Thermal neutral < (200 J/g) 0
Mildly exothermic ( < 600 J/g) 1
Moderately exothermic ( < 1200 J/g) 2
Strongly exothermic (< 3000 J/g) 3
Extremely exothermic (> 3000 J/g) 4
Table 2: determination of chemical Interaction subindex I
INT
Heat of formation Score
Fire 4
Formation of harmless, nonflammable gas 1
Formation of toxic gas 2 – 3
Formation of flammable gas 2 - 3
Explosion 2
Rapid polymerization 2 – 3
Soluble toxic chemicals 1
-no
reactioni
score
=
0
I wastewater
#
methane

26. Table 3: determination flammability subindices I
FL,max
Flammability Score
Nonflammable 0
Combustible (Flash point > 55
o
C) 1
Flammable (Flash point < 55
o
C) 2
Easily flammable (Flash point > 21
o
C) 3
Very Flammable (Flash point < 0
o
C & boiling point < 35
o
C) 4
Table 4: Determination of explosiveness subindex I
EX
Explosiveness (UEL-LEL) vol% Score
Non explosive 0
0 - 20 1
20 – 45 2
45 - 70 3
70 - 100 4
**Note: LEL – lower explosive limit; UEL – upper explosive limit

27. Table 5: Determination of toxic exposure subindices
, I
TOX
Toxic Limit (ppm) Score
TLV > 10,000 0
TLV < 10,000 1
TLV < 1000 2
TLV < 100 3
TLV < 10 4
TLV < 1 5
TLV < 0.1 6
Table 6: determination of corrosivity subindex I
COR
Construction material requires Score
Carbon steel 0
Stainless steel 1
Better material needed 2
**Note: TLV – Threshold limit value

28. Table 7: Determination of Inventory subindex I
I
ISBL OSBL Score
0 -1 tones 0 -10 tones 0
1 – 10 tones 10 – 100 tones 1
10 – 50 tones 100 – 500 tones 2
50 – 200 tones 500 – 2000 tones 3
200 – 500 tones 2000 – 5000 tones 4
500 – 1000 tones 5000 – 10000 tones 5
** Note:
ISBL – inside battery limits
OSBL – outside battery limits
Battery limits - Comprises one or more geographic boundaries, imaginary or real,
enclosing a plant or unit being engineered and/or erected, established for the purpose
of providing a means of specifically identifying certain portions of the plant

29. Table 9: determination of process pressure subindex I
P
Process Pressure Score
0.5 – 5 bar 0
0 – 0.5 or 5 – 25 bar 1
25 – 50 bar 2
50 – 200 bar 3
200 – 1000 bar 4
Table 8: determination of process temperature subindex I
T
Process Temperature Score
< 0
o
C 1
0 – 70
o
C 0
70 - 150
o
C 1
150 - 300
o
C 2
300 - 600
o
C 3
> 600
o
C 4

30. Table 10: determination of equipment subindex (ISBL) I
EQ
Equipment Score
Equipment handling non-flammable, non-toxic material 0
Heat exchangers, pumps, towers, drums 1
Air cooler, reactors, high hazard pumps 2
Compressors, high hazard reactors 3
Furnaces , fired heaters 4
Table 11: determination of equipment subindex (OSBL) I
EQ
Equipment Score
Equipment handling non-flammable, non-toxic material 0
Atmospheric storage tanks, pumps 1
Cooling towers, compressors, blow-down system,
pressurized or refrigerated storage tanks
2
Flares, boilers, furnaces 3

31. Table 12: determination of safe process structures subindex I
ST
Safety level of process structure Score
Recommended (safety standard) 0
Sound engineering practice 1
No data or neutral 2
Probably unsafe 3
Minor accidents 4
Major accidents 5

32. Discussion
A mounded tank is used to store liquefied petroleum gas (LPG)
within a bottling facility. The capacity of the tank is 5000 tones.
The LPG is pumped via a 2 inch pipe line to the bottling plant.
➢Indentify the the elements of ISI that are applicable to the
above industrial facility

33. Total Safety Index (I
TI)
Chemical Inherent Safety Index (I
CI) Process Inherent Safety Index (I
PI)
(a) Subindices for reaction hazard (a) Subindices for process conditions
Item symbolvalue Item SymbolValue
Heat of main reactionI
RM 0 – 4 Inventory I
I 0 - 5
Heat of side reactionI
RS 0 - 4 Process TemperatureI
T 0 - 4
Chemical InteractionI
INT0 - 4 Process Pressure I
P 0 - 4
(b) Subindices for hazardous materials (b) Subindices for process system
Flammability I
FL 0 - 4 Equipment I
EQ
Explosiveness I
EX 0 - 4 ISBL 0 - 4
Toxicity I
TOX 0 - 6 OSBL 0 - 3
Corrosivity I
COR 0 - 2 Process structureI
ST 0 - 5
Is there any reaction?
Is the material
flammable?Can the material
explored?Is the material
toxic?Is the material
corrosive?

34. Total Safety Index (I
TI)
Chemical Inherent Safety Index (I
CI) Process Inherent Safety Index (I
PI)
(a) Subindices for reaction hazard (a) Subindices for process conditions
Item symbolvalue Item SymbolValue
Heat of main reactionI
RM 0 – 4 Inventory I
I 0 - 5
Heat of side reactionI
RS 0 - 4 Process TemperatureI
T 0 - 4
Chemical InteractionI
INT0 - 4 Process Pressure I
P 0 - 4
(b) Subindices for hazardous materials (b) Subindices for process system
Flammability I
FL 0 - 4 Equipment I
EQ
Explosiveness I
EX 0 - 4 ISBL 0 - 4
Toxicity I
TOX 0 - 6 OSBL 0 - 3
Corrosivity I
COR 0 - 2 Process structureI
ST 0 - 5
What is the
inventory?What is the process/storage
temperature?What is the process/storage
pressure?
What are the equipments
within ISBL/in OSBL?
Are there alternative process
structure?

35. Further Reading
Anna Mari Heikkilä, 1999, Inherent safety in process plant design - An
index based approach
➢http://lib.tkk.fi/Diss/199X/isbn9513853721/isbn9513853721.pdf
D.W. Edwards,2005, Are we too Risk-Averse for Inherent Safety?: An
Examination of Current Status and Barriers to Adoption, Process Safety and
Environmental Protection, 83(2):90-100
Maria Papadaki, 2008, Inherent safety, ethics and human error, Journal of
Hazardous Materials, 150(3): 826-830
Mohd Sobri Takriff & Nazatul Naqiah Bahanuddin, 2010, integration of
inherent safety assessment into process simulation, Chemical Engineering
Transaction. 19:397-402
Sven Ove Hansson, 2010, Promoting inherent safety , Process Safety and
Environmental Protection, 88(3):168-172