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14 Human Factors Handbook
• Fatigue – “…the CSB concludes that fatigue of the operations personnel
contributed to overfilling the tower” ( [14]
p.289). Several key operational staff had
worked between 29 and 37 12-hour shifts
in a row.
• Not enough staff – “…operator staffing
levels below the numbers required for
‘safe staffing’. This involves the day-to-day
operation of units with less than the
minimum numbers of operators
required…” ( [14], p.285).
• Supervision – while the start-up shift
started with two supervisors, the experienced supervisor left due to a
family matter, leaving an inexperienced supervisor alone. The remaining
supervisor was busy with several tasks.
• Alarm flood – ISOM operators faced hundreds of alarms going off in a
short time frame. They were not able to assess the situation or warn
others.
There were many factors influencing th e operational decisions and actions.
Deficiencies in each of these factor s combined to exacerbate operational
problems.
2.3.2 Contributing Human Factors
“You cannot change the human condition, but you can change the conditions in
which people work.” Professor James Reason (Chapter 7, page 96) [17].
A Human Factors principle is that errors and
mistakes happen because of a combination of
problems in the working environment and due to
the support, or lack of it, offered by the
organization.
It is important to provide a working envi ronment (or set of conditions) that set
people up to succeed throughout the lifespa n of an operating facility. Establishing
this working environment / set of conditions should begin in the design of each
new facility. Design should include proper Human Factors design in the layout of
systems and equipment, and process hazard analyses and risk assessments must
include consideration for Human Factors.
Human error and
mistakes are not the root
cause of incidents. “…numerous latent
conditions and safety
system deficiencies at
the refinery influenced
their (operator) actions
and contributed to the
accident…”
(CSB, 2007, [14] p.69) |
138 | REAL Model Scenario: Leaking Hoses and Unexpected Impacts of Change
Table 10.1 Results of Study Based on External Incidents (Continued)
Study plan action Feijoada plant finding
Determine potential for multiple
materials to mix inside hoses. If
found, test resistance to mixtures. After careful review of procedures
for flushing hoses and compliance
with the procedures, opportunities
for mixing in hoses were not found.
Determine if leaks or drips might be
impacting hoses. None found.
Evaluate where flexible hoses could
be replaced with hard-pipe
connections. Several opportunities were found,
but none of the hoses in these
services were leakers.
“Maybe we just haven’t been asking the right questions,” Antônio said.
“Let’s take one more walk up to the production floor.” As the four colleagues
walked into the building, Juliana turned to João. “The lighting in here is so much
brighter now since you installed the LED bulbs,” she said. “My mechanics really
appreciate how much better they can see what they’re doing.”
Just then, Antônio noticed Adriana, a new operator, standing on water
feed piping to read a gauge. He opened his notebook to the page where he’d
noted the issue about pipe hangers and showed it to his three colleagues. They
walked over to Adriana. “Are you having trouble reading that gauge?” Antônio
asked her.
“Yes,” she replied. “Ever since the new lights were installed, we get a lot of
glare off the glass. We have to get closer to read a lot of gauges.”
“Does that include the gauges over the raw material manifolds?”
She nodded. “Are you going to tell me we shouldn’t be standing on the
hoses to read those gauges?”
“Or the pipes,” João agreed.
10.6 Prepare
On their way back in the conference room, João said, “Why don’t we have the
operators figure out the best way to read the gauges without standing on the
pipes or hoses?”
“That makes sense,” said Juliana. “I’ll ask my lead mechanic Paulo to
coordinate to make sure maintenance is not affected. |
EVIDEN CE IDEN TIFICATION , COLLECTION & M ANAGEM ENT 149
Furthermore, consideration should be given to the preservation of fragile
physical evidence such as cracks, deposits, chemicals and residues.
8.2.3 Paper Evidence and Data
Although paper data is not always fragile, investigators should place a high
priority on identifying, collecting, and preserving it. Often, the most difficult
issues with paper data are locating the required document s and finding the
relevant information within them. Analyzing paper data can be a very time-
consuming process.
Paper data in the form of operator logs, batch sheets and additions
sheets or logs may be particularly important if reactive chemistry is
suspected. These may hi ghlight the accidental mixing of incompatible
materials, improper sequencing of addi tions, or improper addition rates or
volumes.
The size and scope of the investigation or other factors could mandate
a special document control procedure, wherein each document is given a
unique identification number. In this wa y, there is a documented chain of
custody (e.g., what documents have been collected, the source of the
documents, who has possessed the do cuments at any given time, etc.).
Maintaining a complete, retained document set can help minimize confusion
and a special log can be useful in ma intaining some degree of control over
the flow of paper documents and in fi nding the answers to questions in the
documents when they arise. This is especially important when legal issues or
regulatory agencies are involved.
Paper data from older instrumentation systems such as strip or circular
chart recorders should be controlled immediatel y after the occurrence. Strip
charts and disk recorders will not a ll turn at exactly the same rate, so checking
the turn rate can be critical in comp aring the charts. The measurement range
and units for each pen must also be asce rtained. For crucial charts, it may be
necessary to perform a check of the calibration. If chart recorders are still operating, before removing the charts, mark and
document each one with a
time, then wait 30 minutes or an hour and mark again. Mark each item with
the instrument number or name, the date, time of removal, and the last
position of data recording. Make sure that replacem ent charts are re-
installed after collecting the original on es; key data pertaining to subsequent
occurrences related to the initial event can be lost if the charts are removed
too early or not replenished after removal. |
Piping and Instrumentation Diagram Development
348
The type of gas detection system depends on the types
of gas to detect. In an FGS any aggressive gas can be
decided to be measured. The gas of interest could be a flammable gas, toxic gas, or even inert but suffocating gases like nitrogen gas.
The anatomy of the FGS is very similar to that of a
SIS, except that the final element is not something that interferes with the process (like a switching valve); it is only an alarm.
At the P&ID level, there are two aspects of FGS: its sig-
nal handling system (control system) and the location of sensors and alarms. The signal handling system can be shown in auxiliary P&IDs. Figure 16.28 shows a typical FGS control system that can appear on an auxiliary P&ID.
Figure 16.28 shows a flammable gas detection system
that:
●Has a sensor (“ AE”), transmitter/indicator in field (“ AIT”), indicator in control room through PLC system (“ AI” in diamond).
●Alarms when the flammable gas concentration is 20% of the LEL low explosion level); alarm‐analyte is high level.
Alarm(a) (b)
(c)
(e)(d)TXH
237TAH
237TT
237TAH
237TT
237
TE
237
TAH
237TT
237
TE
237
XL
237TXH
237TAH
237TT
237
TE
237XH
237
TXH
237Horn
Lamp
RTAH
237TT
237
TE
237TE TE
237Logic
Sensor
Figure 16.25 Differ ent ways of showing one alarm system on a P&ID. |
Evaluating Operating Experience Since the Prior PHA 71
during a defined outage, such as a turnaround, may be analyzed under one
“umbrella” MOC, and the potential for complex interactions may similarly
require significant analysis by the revalidation team. However, even simple
changes can have far-reaching effects, for example:
• The decision to introduce a recycle stream could result in
unexpected corrosion or fouling in the equipment, or it could result
in unexpected flow paths during an upset or shutdown.
• A larger pump installed in one uni t might be capable of producing
shutoff head pressures that exceed the design pressure ratings of
equipment in downstream units.
• An interconnecting pipeline might require protection against
overpressure scenarios that could have their initiating event at
either end of the reversible pipeline.
• A liquid nitrogen carryover from the supplier’s facility unit might
cause brittle fracture scenarios during purge activities.
Batch formulation changes, utility system changes or process changes
requiring several new pieces of equipment or extensive piping modifications
might also introduce hazards well be yond the physical boundaries of the
changes. Even simple changes may create a complex situation. When several
small changes are considered collectively, there may be interactions that have a
more significant impact on process risk s. Thus, the more complex the process
changes, the more likely that the Redo approach is warranted.
The degree to which the hazards associated with changes that have been
made were analyzed and how they were analyzed. Continuing the previous
example, assume the company did add a solvent recovery process and
performed the hazard analysis for the MOC in accordance with their core PHA
methodology. So rather than simply document the hazards of the change, they
documented a comprehensive analysis of the hazards, risk controls, and
consequences of their failure. In that ca se, the revalidation team can directly add
the nodes in the project hazard review “mini-PHA” into the existing unit PHA as
they closely review and Update the prior hazard analysis worksheets. That allows
them to identify any oversights while not having to Redo that portion of the PHA.
When MOC teams use the same core anal ysis technique as the PHA, meet the
same analysis requirements (See Chapter 2.), and document them in the same
format as a PHA, the Update approach can be used to efficiently accomplish the
revalidation goals. Conversely, if the so lvent recovery MOC only considered the
“hazards of the change,” the PHA revalidation team may need to Redo the PHA,
at least for the new parts of the process. |
REACTIVE CHEMICAL HAZARDS 87
Incident Investigation – If an operation yields an unexpected result, ask
why did it do that? Through understanding why, you may recognize that
you were heading down the path to an incident. More importantly, now
you know how to avoid it.
Detailed Description
T2 Laboratories Inc. started in 1996 as a solv ent blending business founded by a chemical
engineer and a chemist. One of their products was a blend of MCMT, a gasoline additive. In
2004 T2 began producing MCMT, which be came their primary product by 2007.
The runaway reaction occurred during the fi rst step of the MCMT process. This was a
reaction between methylcyclopentadiene (MCPD) dimer and sodium in diethylene glycol
dimethyl ether (diglyme).
MCPD and diglyme were charged to a 9.3 m3 (2,450 gal) reactor and sodium metal was
added manually through a valve at the top of the reactor, (see Figure 5.3). Heat was applied to
the reactor using hot oil set at 182 °C (360 °F) to melt the sodium and start the reaction to
make methylcyclopentene. Hydrogen was a bypr oduct, vented through a pressure control
valve. At 99 °C (210 °F) the agitator was started (by this time the sodium should have melted).
At 149 °C (300 °F) the heat was turned off. The reaction was known to be exothermic and at
182 °C (360 °F) cooling was applied.
After eliminating other possible causes, the CS B concluded that loss of cooling was the
immediate cause of the runaway reaction. The reac tor was cooled by adding water to the jacket
and allowing it to boil off (Figure 5.3).
The cooling system, necessary to control th e exothermic reaction, could be totally
incapacitated or severely impaired by several single failures: loss of cooling water from supply,
a drain valve left open or partially open, failure of the valve actuators, blockage in the supply
line, temperature sensor failure, or mine ral build up in the jacket. (CSB 2009)
Without cooling, the temperature could continue to rise. Subsequent testing showed that
a second exothermic reaction occurred at 199 °C (390 °F). This reaction was more energetic
than the first, desired reaction. The owner/oper ators of T2 Laboratories did not know about
this second reaction. This reaction generated enough pressure, very rapidly, to burst the
reactor, rated for 41.4 bar (600 psig).
Lessons
Process Safety Culture. In hindsight, it seems the owners of T2 did not have the necessary
process safety competency or know how to build a strong process safety culture.
Compliance with Standards . T2 was not in compliance with the OSHA Hazard
Communication Standard. No written evidence wa s found that T2 had a confined space entry,
lock-out/tag-out, personal protective equipmen t program, or employee training program. |
1.6 Corporate Climate and Chemistry |17
1.6 CORPORATE CLIMATE AN D CHEMISTRY
If process safety culture underpins everything in a PSM S, then
what underpins the culture? What conditions either support or
inhibit the developm ent, m aintenance, and sustainability of the
process safety culture? Mathis and Galloway (Ref 1.5). identify
seven milestones on the safety culture im provement journey. Two
of those m ilestones are climate and chem istry.
Corporate Climate refers to the conditions within an
organization as viewed by its em ployees. In the case of process
safety, m anagement creates an organization’s climate through
four components: Commitment, Caring, Cooperation, and
Coaching. Two organizations may have a common set of activities,
from which an external viewer might infer the same culture.
However, the cultures m ay be very different. For example, soldiers
in com bat and participants in a survival reality TV show may share
som e common tasks, i.e., surviving in harsh outdoor conditions,
but the climate or environment for these two situations are totally
different and therefore the cultures will be very different.
Corporate Chemistry refers to the structure of the culture. Like
the elem ents that make up a molecule or the elements in the soil
that nurtures the growth of plants, safety culture is built around
the elem ents of Passion, Focus, Expectations, Proactive
accountability, Reinforcement, Vulnerability, Communication,
Measurement, and Trust. (Ref 1.5).
In developing the culture principles presented in this book,
CCPS considered both climate and chemistry. Som e culture
principles addressed both climate and chem istry, as shown in
figure 1.2, facing.
1.7 SUMM ARY
Process safety culture has been recognized as a contributing
factor in m any significant incidents that have occurred in the
processing industries in recent years. Process safety culture in any |
Preparing for PHA Revalidation Meetings 109
needed, unless the team that has been studying the other nodes have that
knowledge. Another consideration is that in addition to the required skills, there
may be other required qualifications. For example, engineering expertise may
have to be provided by degreed engineers in particular disciplines or with
particular licenses. Operations expertis e may have to be provided by hourly
employees or field supervisors.
Two options for selection of PHA
revalidation team members include (1)
for efficiency, keep the same team as
before, or (2) for objectivity, select a new
team. Either approach can be defended
on its merit. If the Update approach is
selected, the same team may be
preferred, but organizational issues (e.g.,
loss or reassignment of past team
members) often prevail, and the team ends up as a mix of new personnel and
personnel who were involved in the prior PHA. If the Redo approach is selected,
a substantially or completely different team is more commonly used and
sometimes required. In addition, review of the prior PHA may indicate the need
to supplement the revalidation team with members having specific areas of
expertise not present on the prior team (e.g., metallurgist, control engineer,
chemist, loader/unloader). Some of th ese team members may be part-time or
on-call members.
As is the case with any initial PHA, th e study leader should make every effort
to ensure that the proposed revalidation team has a proper mix of knowledge,
experience, and training. For the revalidation to be effective, participants should
have specific knowledge of the process be ing evaluated in addition to general
subject matter knowledge. Thus, most orga nizations have individual or collective
experience requirements. Fo r example, at least one of the individuals providing
operations expertise might be required to have been a qualified front-line
operator for at least five years and to have worked in the subject unit for at least
two years. Alternatively, collectively am ong the revalidation team participants,
the organization might require at least three years of operating experience on
the subject unit.
Some organizations also place maximum requirements on individual job
roles or experience. The concern is that an individual with decades of experience
or a senior management position mi ght dominate the team discussions,
particularly if others have minimal or no experience with the subject process.
Thus, they write their team composition rules to favor teams with a range of
experience, believing that inherently le ads to more diverse opinions and better Team Members for Redo
If the PHA is being Redone
because of quality or complete-
ness issues, it is usually better
to select new team members
with a different study leader. |
EQUIPMENT FAILURE 201
generated more heat and provided fuel for the flames to propagate back to the tank.
(Sherman)
Design considerations for process safety. Distillation is temperature, pressure, and
composition dependent; special care must be taken to fully understand any potential thermal
decomposition hazards of the chemicals involved.
Columns need adequate instrumentation for monitoring and controlling pressure,
temperature, level, and composition. The location of sensing elements in relation to column
internals must be considered so that they provide accurate and timely information and are in
direct contact with the process streams.
A design feature of some columns is to prov ide a tall base (e.g. 3 m (10 ft)) to provide
adequate Net Positive Suction Head (NPSH) to ensure that the bottoms pumps do not cavitate
and fail. This also reduces the wetted area exposed to a ground-level fire.
Leaks from where piping or instrumentation is connected to these vessels is a common
failure. Where the material is flammable, a fire can occur that can impact surrounding
equipment. Column support structures and skirts should be fireproofed, as they are not cooled
by internal fluid flow and a ground fi re can lead to the column collapsing.
Overpressurization can result from freezing , plugging, or flooding of condensers, or
blocked vapor outlets, if the heat input to the system is not stopped. API RP 520 Sizing, Selection,
and Installation of Pressure-Relieving Devices and API RP 521 Pressure-Relieving and Depressurizing
Systems provide extensive guidance on the placement and sizing of pressure relief valves and
other overpressure protection sy stems. (API RP 520, API RP 521)
Emphasis should be placed upon the use of inherently safer design alternatives using
concepts such as the following.
Limiting the maximum heating medium temperature to safe levels
Selecting solvents which do not require removal prior to the next process step
Using a heat transfer medium that prevents freezing in the condenser
Locating the vessel temperature probe on the bottom head to ensure accurate
measurement of temperatures, even at a low liquid level
Minimizing column internal inventory
Avoiding dead legs that can corrode, plug or freeze
To prevent packing fires:
Cool columns to ambient temperature before opening
Wash the column thoroughly to remove residues and deposits
Use chemical neutralization to remove pyrophoric material
Purge columns with nitrogen
Monitor temperatures of the packing and column as it is opened
Minimize the number of open manways to reduce air circulation
|
176 INVESTIGATING PROCESS SAFETY INCIDENTS
Figure 8.9 Sequence Diagra m for Tank Overflow Example
8.5 SUM M ARY
Careful, complete and effective eviden ce gathering is ke y to a successful
investigation. Evidence can be ph ysical (damaged equipment, parts,
materials, residues etc.), paper records, electronic data or position data.
Consider the fragility of the evidence when determining priorities for the
investigation team. Preservation of fragile evidence, su ch as electronic
process data, is a key factor. The te am members may have to work several
paths simultaneously and the need for additional skill sets should be
identified quickly. Agreement between interested parties about how the
evidence is handled can be supported us ing protocols. It is important to
establish a system for do cumenting and securing evidence and a chain of
custody is required for items that are moved betw een locations or different
parties. Photography is used extensivel y to record evidence and can also be
an inherent part of the chain of cust ody process. A set of tools and other
equipment should available for meas uring, inspecting, recording and
preserving evidence. Timelines and se quence diagram are effective tools to
document events and cond itions and identify gaps that require further
evidence gathering.
|
306 Human Factors Handbook
The last step before signing a Permit to Work should be a field visit of
Operations personnel together with the pe rson responsible of the contractor crew
to check the real conditions before any activity starts. This provides a last
opportunity to identify any unusual situation or hazard.
Coordination
This can include:
• Communicating and coordinating – holding communication and
coordination sessions daily, where a ll tasks over the next 48 hours are
reviewed for potential conflict or o verlap. Drawings and plans can be
shared and discussed.
• Zonal control – this is where multiple contractors may be operating in
the same area. Identified areas are defined for “zonal control”, with each
zone supervised by an identified co ntractor or by client personnel.
• Notice boards or asset maps – thes e should show all daily and planned
activities, each contractor color-coded, so it is clear which teams are
working in which parts of the plant.
Double-checking task completion
Some examples include:
• The client supervisor performing a “w alk-down” before the start of work
and at the end of each shift. This is to check the site is safe and that site
housekeeping is in order.
• Additional checks on the safe completion of tasks such as isolation and
whether a system is safe to restore to service.
• Higher levels of checks on task completion during peak periods and
critical points e.g., restored to service.
• Using independent specialists to check work of other specialist
contractors.
Double-checking tasks is important a) wh ere contractors are scheduled to work
on systems that normally contain hazardou s substances or energy sources, and b)
where a system is to be started or restor ed to service after a contractor completes
a task.
It is important that double checking is undertaken by an independent person
not part of the contracting team. Ch ecks completed by colleagues may be
unreliable because they assume that the other’s work is trustworthy.
Demobilization
An explicit demobilization activity can help to ensure that site restoration and
reinstatement is performed without omission or miscommunication. |
463 |
17. Error management in task pla nning, preparation and control 209
Table 17-5 continued
Human Factors good practice for isolation
9. P&ID, schematics, or their equivale nt, should clearly indicate all
connections and routes by which produc t may, for example, enter a vessel,
to allow all required isolation points to be identified.
10. P&ID, schematics, power supply diag rams, or their equivalent, should
clearly indicate all associated equipment that needs to be deactivated to
prevent accidentally restoring supply to isolated systems.
11. P&ID should be marked up to show the connected lines/systems, the isolation valves and spading (blinding) points, test points etc. to help visualize the extent of the isolation envelope.
12. The line should be walked as part of the development of the isolation plan, to confirm the plan with the workers.
13. The open/closed position of isolation valves should be visible and unambiguously indicated. It should be possible to verify the isolating valve
is 100% closed and not allowing gas or liquid to pass through.
14. It should be possible to tag and lock off manually operated isolation valves,
blinds, power supplies, and other isolation equipment.
15. Include a test or “try step” to verify isolation before commencing works. This should be a positive method of verifying isolation or disabling of energy sources.
16. There should be a test/sampling point for each and every section of isolatable pipework, vessels, and other equipment.
17. Testing points, such as sample outl ets and pressure valves, should be
accessible.
18. Isolation and bleed points should be close to the point of maintenance (to
aid task coordination).
19. Ensure physical access and lighting for all isolation, blinding, and bleed
points.
20. The “line” should be walked, by someone who did not perform the isolation. to verify it is in a safe st ate prior to hand back to operations.
21. All Permit to Work (PTWs) and other job aids should include unambiguous
Stop or Hold Points for isolation to be verified and recorded before work
begins or continues.
22. Documentation and status boards should unambiguously and simply represent the system state.
23. Shift handover systems should clearly communicate the system status.
24. Compliance with isolation requirements should be treated as mandatory.
25. A contemporaneous record of isolations should be documented to reduce the risk of missing an isolation (for example via an isolation certificate/
checklist).
26. Any variation to the isolation procedure must be authorized.
|
92 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
Table 5.1. Chemical Reacti vity types and examples
(Crowl 2019)
Reactive Type Example
Pyrophoric and spontaneously
combustible Readily reacts with oxygen, igniting and burning
Aluminum alkyls, Raney nickel catalyst
Peroxide-forming Reacts with oxygen to form unstable peroxides
1,3, butadiene
Water reactive chemical Sodium, titani um tetrachloride, boron trifluoride
Oxidizer Readily yields oxygen or other oxidizing gas to
promote or initiate combustion
Chlorine, hydrogen peroxide, nitric acid, HF
Self-reactive Butadiene polymeriza tion, acetylene decomposition,
ethylene and propylene oxide, styrene, vinyl acetate
Chemical incompatibles Caustic + muriatic acid
Impact sensitive or thermally
sensitive Trinitrotoluene (TNT)
Runaway reactions Ethylene
Table 5.2. Some Reactive Functional Groups
(Crowl 2019)
Some Reactive Functional Groups
Azide N3
Diazo -N=N-
Nitro -NO2
Nitroso -NO
Nitrite -ONO
Nitrate -ONO2
Fulminate -ONC
Peroxide -O-O-
Peracid -CO3H
Hydroperoxide -O-O-H
Ozonide O3
Amine oxide ≡NO
Chlorates ClO3
The key point is to either prevent the chemical re action, or, if it is desired, to ensure that
it can be safely contained in the equipment. The fi rst step in managing chemical reactivity is to |
92 Guidelines for Revalidating a Process Hazard Analysis
5.1.2 Redo
The Redo approach is usually selected when an Update of the prior PHA is
impractical or too complex. This is base d on the evaluation of the prior PHA with
respect to the criteria as described in Chapter 3 and the evaluation of recent
operating experience as described in Chapter 4. In this approach, the
revalidation is essentially a new PHA. Th e team starts from the beginning and
performs the entire PHA in detail as if it were an initial PHA. Figuratively, the
team starts with blank analysis worksheets, but in practice, most use some
information from the previous PHA as a reference or guide.
A Redo may be the most appropriate choice in situations where significant:
• Changes have occurred to PHA requirements or analysis methods
• Gaps or deficiencies have been discovered in the process safety
information used as the basis for the prior PHA
• Gaps or deficiencies exist in the prior PHA documentation, analysis
method, or the manner in which it was conducted
• Changes, particularly un-
controlled changes, have
occurred in the process or
equipment since the prior
PHA was conducted
• Incidents show gaps or
errors in the prior PHA
The Redo approach involves
conducting a PHA of the process
using one or more methodologies
that are appropriate for the hazards
and complexity of the process. The
requirements and activities for a
Redo generally parallel those of an
initial PHA. Significant instructional
information is available elsewhere
(e.g., in the CCPS book Guidelines for
Hazard Evaluation Procedures [2]) on
the conduct of initial PHAs. Changing the Core PHA
Methodology
The decision to Redo a PHA offers
the opportunity to reconsider the
choice of hazard evaluation core
methodology to be used (e.g.,
HAZOP Study, rather than What-
If/Checklist).
If a methodology substitution is
made, it should be with the intent of
enhancing the quality of the PHA,
and not at the expense of accuracy
or thoroughness. Section 3.1.1
discusses technique selection in
light of the nature of the process
and its hazards. |
24. Human Factors of operational level change 311
24.4 Recognizing operational level changes that impact human
performance
24.4.1 The need for early recognition
In any organization, changes should be
recognized and managed.
Some impacts are less obvious
(latent as in Figure 24-1) or may be
delayed. If “hard evidence” of
immediate adverse impacts on human
performance is demanded before
taking action, this may cause failure to
manage changes effectively.
24.4.2 Immediate impacts
Some changes and their potential impacts are more obvious and immediate.
These include the following examples:
• Retraining of people on a new control system, a major change to a
process, or new operations.
• A major change to staffing levels, such as moving from 10 to seven
people per shift team.
• A major change to supervision, such as removing team leaders.
• The change of the person staffing a key role such as Emergency
Response Commander.
• A change in piping and instrumentation, requiring a revision of Piping
and Instrumentation Diagrams.
24.4.3 Latent impacts
Some impacts may not be immediate nor obvious. The
impact is hidden until circumstances occur to reveal it,
such as a process upset. For example:
• The installation of new, high reliability, or
automated process equipment ma y reduce the frequency of
maintenance and emergency response . This could lead to a lower
frequency of performing tasks, whic h can cause skill fade. This increases
the likelihood of mistakes when the task is performed.
• The centralization of control rooms ma y reduce the frequency of control
room operators working outside, and lead to a gradual reduction in their
level of local plant knowledge. This would only be revealed when a
process upset occurred.
Latent impacts
occur sometime
after the change
has occurred.
Immediate
Latent
Figure 24-1: Types of change and
impact |
34 GUIDELINES FOR MANAGING ABNORMAL SITUATIONS
History indicates that abnormal si tuations that are not immediately
recognized or effectively addressed ca n escalate at a facility, resulting in
one or more of the following:
Chemical release or fire leading to injuries or fatalities
Equipment and property damage
Environmental impact or non-compliance
Business interruption
Loss of community confidence/ reputational damage
Two often-referenced abnormal situation incidents are Union
Carbide’s chemical release in Bhopal, India in 1984 and the BP Texas City
refinery isomerization unit explos ion in 2005 (CCPS 2008a). As
summarized in Example Incident 3.2 and Example Incident 3.3, both
events included significant precurso rs that were allowed to continue,
resulting in abnormal situations that led to major consequences.
Example Incident 3.2 – Union Carbide, Bhopal, India 1984
On December 3, 1984, the Union Carbide plant located about 3 to 4
miles (5 to 7 km) outside the cent er of the city of Bhopal, India
accidentally released into the at mosphere approximately 40 metric
t o n s o f m e t h y l i s o c y a n a t e ( M I C ) , an intermediate chemical used in
production of carbaryl (a pesticid e). The incident resulted in the
fatalities of approximately 4,000 people living near the plant and the
subsequent fatality of over 16,000, as well as injuries in 200,000 and
genetic mutations to affect severa l generations of offspring (Gupta
2004).
The incident originated from one of the three MIC storage tanks,
which were refrigerated, partially buried, and equipped with relief
valves that discharged to a flar e tower through a caustic soda
scrubber. At the time of the acci dent, the MIC plant had been shut
down for over a month, but carbaryl production was allowed to
continue, using the inventory left in the storage tanks.
|
11.2 Seek Learnings | 145
Lucas next set up a meeting with Mason to discuss the survey. He was able
to win Mason over with his focus on the business case for process safety. Like
Oliver, Mason told Lucas that the survey should not impact operational
efficiency.
Lucas told Charlotte of the compromise, and she quickly went to work
setting up a survey. She thought to herself, “While I’m at it, I’ll throw in a couple
of questions to see what people think of the process safety culture on this rig.”
A few weeks later, the results were in. Charlotte analyzed the results and
immediately took them to Lucas. She said, “Looks like we have a problem here.
Fatigue is definitely an issue and perhaps even more problematic is the
process safety culture. Seems like folks are willing to cut corners to meet
production numbers.”
Lucas was distressed by the results. He thought of his chats with Oliver
and Mason, when he had reminded them that fatigue was often a cause of
major accidents. Poor process safety culture falls into that category too. He
told Charlotte, “We have to make a case for improving our process safety
culture before we meet with Mason. Let’s start by looking for external
incidents and see what we can learn.”
Lucas continued, “Charlotte, you’re probably too young to remember the
Space Shuttle disasters. But let’s put it this way, there was so much pressure
to get the shuttle off the ground that the management ignored the engineers’
warnings. We can’t let that happen to us on this rig.” Charlotte nodded in
agreement. She may not have been born when the Challenger exploded, but
she remembered her parents talking about the incident when she was growing
up.
11.2 Seek Learnings
Charlotte quickly found several relevant major offshore incidents, including
some that were in their region:
Piper Alpha, North Sea, UK, 1988
Communications broke down from one shift to the
next aboard the Piper Alpha oil and gas rig. One of
the pumps was shut down for maintenance and had its pressure relief
valve removed. A work permit for this pump was neither clearly displayed,
nor communicated during a shift change. When a blockage occurred in
the other pump, the pump that was undergoing maintenance was put See Appendix
index entry S1 |
51
Table 3.1: Effect of Reactor Design on Size and Productivity for a Gas-
Liquid Reaction (Ref 3.2 CCPS)
Reactor Type Batch Stirred Tank
Reactor Loop Reactor
Reactor Size (l) 8000 2500
Chlorination Time (hr) 16 4
Productivity (kg/hr) 370 530
Chlorine Usage (kg per 100 kg product) 33 22
Caustic Usage in Vent Scrubber (kg per 100 kg product) 31 5
3.6 REACTIVE DISTILLATION
The combination of several unit oper ations into a single piece of
equipment can eliminate equipment, minimize the inventory of
reactants, and simplify a process. However, there may be inherent safety conflicts resulting from this strategy (see Chapter 12). Combining several
operations into a single device incr eases the complexity of that device,
but it also reduces the number of ve ssels or other pieces of equipment
required for the process. Careful eval uation of the options with respect
to all hazards is necessary to select the inherently safer overall option.
Reactive distillation is a techni que for combining several process
operations in a single device. One company has developed a reactive distillation process for the manufacture of methyl acetate that reduces
the number of distillation columns fr om eight to three, while also
eliminating an extraction column and a separate reactor (Ref 3.1 Agreda;
Ref 3.4 Doherty; Ref 3.19 Siirola). Inventory is reduced and auxiliary
equipment, such as reboilers, cond ensers, pumps, and heat exchangers |
90 Guidelines for Revalidating a Process Hazard Analysis
5.1 REVALIDATION APPROACHES
The two revalidation approaches (introdu ced in Section 1.5) are described in
detail in the following sections.
5.1.1 Update
The Update approach is an incremental revision to an existing analysis to reflect
the operational experience since the prio r PHA was conducted, as discussed in
Chapter 4. An Update is generally a less laborious option than a Redo and is a
viable option for high-quality PHAs (as di scussed in Chapter 3) of processes at
facilities where changes have been effect ively managed and few or no significant
incidents have occurred. In these si tuations, the revalidation team can
systematically reaffirm the validity of risk judgments documented in the prior
PHA and Update i t w i t h t h e r e s u l t s f r o m r e l e v a n t m a n a g e m e n t o f c h a n g e
(MOC)/pre-startup safety review (PSSR) reviews and incident investigations.
Two common ways of Updating a PHA include:
Detailed Review. The detailed review is similar to Redoing the PHA, but should
entail less time and effort, because the content of the PHA report is only
amended on an “as-needed” basis and not always developed from first
principles. Each section or node of the core hazard analysis, as well as any
complementary analysis (such as a huma n factors checklist), in the PHA is
reviewed in detail. Changes are discussed to determine their potential impact on
previously documented scenarios, or to determine if new scenarios need to be
added. (See Section 4.2.1.) Changes implemented in response to prior PHA
recommendations or incident investigation s are included in this review. (See
Section 3.3.1.) They typically result in revisions to the list of safeguards, but they
may also affect other portions of the PHA worksheets. Those scenarios affected
by the changes, new learnings, or incidents need to be thoroughly addressed,
and necessary changes in the PHA are recorded in the PHA documentation (e.g.,
HAZOP worksheets, Checklist responses.)
Change and Incident Review. Alternatively, the revalidation team may choose
to review only the changes and incidents that have occurred since the prior PHA.
The revalidation team, with appropriate reference to the prior PHA, discusses
the significance of the changes and incidents, and then documents their
deliberations and decisions. The revalidation team may use a separate
worksheet, and the information recorded us ually includes a description of each
change (or incident), its process safety significance, and any risk management
decisions or recommendations made. (See Se ctions 3.3.1, 4.2.1, and 4.2.2.) Either |
Table 14-1: Suitability of and differences between competency assessments
Assessment
Method Type of human
performance Advantages Disadvantages Issues to consider
Verbal
Questioning
“What if”
scenarios Suitable for
knowledge-
based
competency • Useful for investigating
knowledge
• Can be standardized
• Valuable tool for
collecting evidence
across activities • Not sufficient enough in
itself to demonstrate
competency
• Least likely to be
representative of real
work conditions
• Assessors may answer
their own questions • Assessors should be
trained and experienced
in the use of questioning
techniques
Written exam Suitable for
knowledge-
based
competency • Valuable for knowledge-
based activities
• Can be well structured
and standardized • Requires assessment time
for those being assessed
and for the assessors, and
time for the scorers
• Requires time away from
job • Requires skilled
assessors to assess the
outcome
• Danger that knowing is
confused with being able
to do
• Provides supplementary
evidence of actual
performance
|
94 | 7 Keeping Learning Fresh
Another visual-spatial technique is a drawn diagram. T.J. Larkin, a well-
known safety communicator, advocates hand-drawn diagrams over
photographs for highlighting the issue for the same reason that animation is
preferred over actual video of an incident–their simplicity makes it easier to
focus on the important details (Larkin 2012). Repsol provided an example of
such a diagram addressing a utility service contamination event, an excerpt of
which is reproduced as Figure 7.1.
Figure 7.1 Simple Drawn Diagram Example (Source: Repsol, reproduced with
permission)
Finally, it can be remarkably effective to leave evidence of past incidents
in place to serve as a daily reminder of why we must do what we do. One
company left shrapnel from a significant explosion lodged in a wall, with a sign
commemorating the event. Another company has a framed photograph
showing the plant on fire hanging by the employee entrance, with the caption,
“Never again. We all know what we must do.” The learning model scenarios in
Chapters 9, 10, and 11 use posters with graphics and/or videos to stress the
importance of proper safety practices.
To communicate visually about responding to person-down incidents you
could create a video, as mentioned in Section 7.1. Alternatively, you could draw
a simple poster, such as shown in Figure 7.2 (facing page).
|
Pumps and Compressors
179
to the control valve to open and open further, and this is
why it doesn’t keep up with the low flow.
The other option is a loop similar to the flow control
loop but a pressure control loop. In this design, instead of a flow sensor we install a pressure sensor and the loop is a pressure loop. This control system doesn’t work for all conditions as it only can work when the pump care is adequately steep.
It is generally justifiable to use a control system on the
minimum flow protection pipe for larger pumps, say larger than 35 hp.
For smaller pumps a similar system could be used, but
instead of a control system we can have an on/off system. This means the flow sensor is still used but instead of a control valve a searching valve can be used. Whenever the pump flow goes below the minimum flow this valve will be opened to recirculate some flow to increase the pump flow rate to a value higher than the minimum flow. As you can see this is not a very accurate way to adjust the flow to protect the pump against the minimum flow conditions. However, for smaller pumps, say less than 35 down to about 20 hp, it is not justifiable to use a more expensive control loop and instead this switching loop is used (Figure 10.9).
For smaller pumps less than 20 hp a continuous mini-
mum flow is implemented for the pump. In such cases just a restrictive orifice (RO) could be used on the minimum flow protection pipe (Figure 10.10).
For very small pumps, say less than 5 hp, as was men-
tioned there is no need to consider implementing a minimum flow pipe at all.
It is important to realize that a minimum flow protec -
tion pipe is not working during the majority of pump operation. It is because in the majority of times the con-trol valve on the minimum flow protection pipe is closed. This valve will be open only when the flow to the pump goes below the minimum flow value (Figure 10.11). This is the reason that some companies violate their pipe sizing criteria and use higher velocity design bases for a pipe to come up with a narrower and cheaper pipe for this purpose.
However, the control valve on minimum flow protec -
tion pipe should be “failed‐open” (FO). This valve should be FO because it’s function is important to keep the pump operational. When losing the instrument air if this valve is “failed‐closed” (FC) the pump will start to vibrate if the flow goes below the minimum flow value. So to keep the pump operational this valve should be FO.FC
Figure 10.9 Minimum flo w protection pipe with switching loop.
RO
Figure 10.10 Minimum flo w protection pipe with restrictive
orifice.
Senses more than 10 0 m3/hr
so closes the va lve
Senses less than 10 0 m3/hr
so opens the va lve165 m3/hr0 m3/hr FV
FVFC
FCFX
FXFT
FTFIC
FIC
165 m3/hrMinimum flow:
100 m3/hr
20 m3/hr
80 m3/hr
80 m3/hrFigure 10.11 Func tioning of a minimum flow
protection pipe. |
20. Situation awareness and agile thinking 253
• An overreliance on general expe ctations about how the system
functions, in the absence of real-time data.
• Several pieces of information may not have been registered by the
operator due to cognitive capacity limitations (e.g., limits to working
memory).
20.4 Causes of poor situation awareness and rigid thinking
20.4.1 Factors influencing situation awareness
Operators’ situation awareness is influenc ed by several factors. These factors may
reduce operators’ cognitive capacity and impair their performance. They include:
• Experience and training.
• Time pressure and workload.
• Motivation, stress levels, and work fatigue.
• Coordination with team members, and dependence on others.
• Weather conditions (visibility), eq uipment, and process noise.
• Complexity of the process.
• Location or site of the plant.
• Abnormal situations.
Mica Endsley and Debra Jones in their book “SA Demons: The Enemies of
Situation Awareness” [84] identified ei ght causes responsible for failures in
situation awareness. Those were termed as demons of situation awareness and
include:
1. Attention tunneling - focus on certain type of information and excluding
the rest.
2. Requisite Memory Trap – reliance on memory information, despite
human memory limitations.
3. Stress, anxiety, fatigue and other stressors – stress and fatigue impair
working memory.
4. Data overload- more data is ava ilable than the human cognition can
process.
5. Misplaced salience –the way information is presented (e.g., bright colors
and flashing lights) overwhelm and misdirect operators' attention.
6. Complexity creep - the more complex the system the more difficult it is
for operators to develop accurate comprehension of the situation.
7. Errant mental models – incorrect mental model may lead to inaccurate
interpretation of data.
8. Out-of-the -loop syndrome – highly automated systems may result in
operator shaving low awareness of the systems.
|
1.7 Summary |19
facility form s the foundation of the PSM S, regardless of what is
written. The quality of demonstrated leadership directly affects
the strength and quality of the process safety culture, and the
quality and health of the process safety program itself. While
m anagers of PSMS’s clearly serve as process safety leaders, all
m anagers and executives in enterprises that manage m ajor
process hazards can and indeed should demonstrate process
safety leadership and help set a strong, positive culture.
CCPS defines process safety culture as:
“The pattern of shared written and unwritten attitudes and
behavioral norms that positively influence how a facility or
company collectively supports the development of and successful
execution of the management systems that comprise its process
safety management system, resulting in the prevention of process
safety incidents.”
Other definitions related to safety culture and particularly
process safety culture can be found in the literature. There is no
single definition of safety or process safety culture. Numerous
definitions have been presented in the literature in recent year.
The CCPS definition embodies all the lessons learned in the
literature to produce a definition serving the m ajor hazard
industries ranging from upstream oil and gas, through refining,
chem icals and pharm aceuticals to manufacturers who handle
chem icals and practice chem istry in other industries.
Process safety culture and the organizational culture that it fits
into are strongly linked. The process safety/safety culture of an
organization cannot exist in a vacuum. Any problem s or issues in
the organizational culture will also show up in the process safety
culture, and elsewhere in the organization as well. Likewise,
efforts to improve process safety culture can spill over to
positively impact the overall culture of the organization.
Organizations that have a strong overall culture and strong process |
6. Simplify – An Inherently Safer Strategy
In the context of inherent safety, simplify means designing and/or
operating the process to reduce or eliminate unnecessary complexity in
order to reduce or eliminate the ch emical hazard. Reducing complexity
helps to accomplish a number of goals, for example: 1) minimization or
elimination of extra equipment that can fail and contribute to a process
safety incident, and 2) reducing or eliminating extra processing steps
with hazardous conditions or whic h may result in a release of the
hazardous chemicals or energy, or (3 ) reducing the use or the number of
chemicals necessary in a process. A simpler process is generally safer
and more cost-effective than a compl ex one. Kletz (Ref 6.9 Kletz 1998)
offered several reasons why proce ss designs are unnecessarily complex:
The need to control hazards . Instead of avoiding hazards using
inherently safer design principles, most designers choose to
control them actively using controls, alarms, and safety
instrumented systems.
The desire for technical elegance . To some designers, simple
equates to crude or primitive, whereas, if carefully designed, a
simple process can achieve what it needs to do without excess
equipment. A simple process design including only the essential
elements to safely carry out its intended task(s) is more elegant
than a complicated process th at does the same thing.
The failure to carry out hazard an alyses until late in the design . PHAs
and similar studies performed late in the design usually result in
more active controls and equipment rather than more inherently
safer solutions. If a preliminary PHA or similar hazard analysis
technique is performed at the conc eptual stage of the project, it
may be easier to incorporate IS techniques, especially
substitution or elimination.
Following standards and specifications that are no longer
appropriate or not completely applicable . Active solutions to
potential hazards that are sometimes contained in design /
engineering standards and specifications can accumulate in a
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Appendices 191
Q T R
• Contamination of utilities (e.g., water)?
• Contamination from spills or runoff?
• Noise?
• Transport of hazardous materials from other sites?
• Flooding (e.g., ruptured storage tank)?
VII. Unit Layout
Are large inventories or release po ints for HHCs located away from
vehicular traffic within the plant?
Could specific siting hazards be posed to the site from credible
external forces such as high winds, earthquakes and other earth
movement, utility failure from outside sources, flooding, natural fires,
ice accumulation, and fog?
Is there adequate access for emerge ncy vehicles (e.g., fire trucks)?
Are access roads free of the possibility of being blocked by trains,
highway congestion, spotting of rail cars, etc.?
Are access roads well engineered to avoid sharp curves? Are traffic
signs provided?
Is vehicular traffic appropriately restricted from areas where
pedestrians could be injured or equipment damaged?
Are cooling towers located such that fog that is generated by them
will not be a hazard?
Are the ends of horizontal vessels fa cing away from personnel areas?
Is hydrocarbon-handling equi pment located outdoors?
Are pipe bridges located such that they are not over equipment,
including occupied structures and administration buildings?
Is piping design adequate to withstand potential liquid load?
VIII. Location of the Unit Relative to On-site and Off-site Surroundings
Is a system in place to notify neighboring units, facilities, and
residents if a release occurs?
Are the detection systems and/or alarms in place to assist in warning
neighboring units, facilities, and residents if a release occurs?
Do neighbors (including units, facilit ies, and residents) know how to
respond when notified of a release? Do they know how to shelter-in-
place and when to evacuate?
Are large inventories or release po ints for HHCs located away from
publicly accessible roads?
Is the unit, or can the unit be, located to minimize the need for off-
site or intra-site transporta tion of hazardous materials?
Are workers in this unit protected from the effects of adjacent units
or facilities (and vice versa), and are environmental receptors and the
public also protected from the following: |
GLOSSARY xxv
Integrity
Operating
Window An Integrity Operating Window (IOW) is a set of
limits used to determine th e different variables that
could affect the integrity and reliability of a process
unit. An IOW is the set of limits under which a
process, piece of equipment, or unit operation can
operate safely. Working outside of IOWs may cause
otherwise preventable damage or failure.
Lagging Metric A retrospective set of me trics based on incidents
that meet an established threshold of severity.
Layer of
Protection
Analysis (LOPA) An approach that analyzes one incident scenario
(cause-consequence pa ir) at a time, using
predefined values for the in itiating event frequency,
independent protection layer failure probabilities,
and consequence severity, in order to compare a
scenario risk estimate to ri sk criteria for determining
where additional risk reduction or more detailed
analysis is needed. Sc enarios are identified
elsewhere, typically using a scenario-based hazard
evaluation procedure s uch as a HAZOP Study.
Leading Metric A forward-looking set of metrics that indicate the
performance of the key wo rk processes, operating
discipline, or layers of protection that prevent
incidents.
Loss of Primary
Containment An unplanned or uncontrolled release of material
from primary containment, including non-toxic and
non-flammable materials (e.g., steam, hot
condensate, nitrogen, compressed CO 2 or
compressed air).
Management of
Change A management system to identify, review, and
approve all modifications to equipment,
procedures, raw materials, and processing
conditions, other than replacement in kind, prior to
implementation to help ensure that changes to
processes are properly analyzed (for example, for
potential adverse impacts), documented, and
communicated to employees affected. |
3.7 References |105
3.11 Smith, J., & Foti, R., A pattern approach to the study of leader
emergence , The Leadership Quarterly, Vol. 9, 1998.
3.12 Foti, R., & Hauenstein, N., Pattern and variable approaches in
leadership emergence and effectiveness , Journal of Applied
Psychology, Vol. 92, 2007.
3.13 Scouller, J. (2011). The Three Levels of Leadership: How to Develop
Your Leadership Presence, Knowhow and Skill . Cirencester:
M anagement B ooks 2000.
3.14 Stricoff, S., What Process Safety Needs in a Leader , Safety + Health,
2013.
3.15 United Kingdom Health and Safety Executive (HSE), Safety and
environmental standards for fuel storage sites , Process Safety
Leadership Group , Final report , 2009.
3.16 CCPS, Recognizing Catastrophic Incident Warning Signs in the Process
Industries, American Institute of Chemical Engineers, New York, 2012.
3.17 Mathis, T., Galloway, S., STEPS to Safety Culture ExcellenceSM, Wiley,
2013.
3.18 Paradies, M., Has Process Safety Management Missed the Boat?
AIChE, Process Safety Progress, Vol. 30, No. 4, 2011.
3.19 Elliot, M ., et. al., Linking OII and RMP data: does everyday safety prevent
catastrophic loss? International. Journal of Risk Assessment and
M anagement, Vol. 10, Nos. 1/2, 2008.
3.20 Organization for Economic Cooperation and Development (OECD),
Corporate Governance for Process Safety, OECD Guidance for
Senior Leaders in High Hazard Industries, J une 2012.
3.21 United Kingdom Health and Safety Executive (HSE) Health & Safety
Laboratory, Safety Culture: A review of the literature , HSL/2002/25,
2002.
3.22 Oracle, An Oracle White Paper, Seven Steps for Effective Leadership
Development , J une 2012.
3.23 Baker, J .A. et al., The Report of BP U.S. Refiner ies Independent Safety
Review Panel , J anuary 2007 (B aker Panel Report).
3.24 HR Council, HR Planning, Succession Planning
(http://hrcouncil.ca/hr-toolkit/planning-succession.cfm) |
68 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
Figure 4.13. Degrees of congestion from low to high (left to right)
(BakerRisk 2001)
Understanding, modeling, preventing, and mitiga ting vapor cloud explosions is an area of
significant focus in industrial facilities handlin g flammable materials due to the harm they can
potentially cause. Many signific ant process safety . events have highlighted the importance of
this focus and the importance of locating and de signing buildings so as to protect occupants.
API RP 752, 753 and 756 provide guidance on blast-resistant design of permanent structures,
portable structures, and tents, respectively. Th e CCPS “Guidelines for Evaluating Process Plants
Buildings for External Explosions, Fires, and Toxic Releases” provides detailed guidance on
multiple explosion modeling methods. Methods us ed in modeling explosions are discussed in
Chapter 13.
Physical Explosions
Overpressure – Any pressure above atmospheric caused by a blast.
(CCPS Glossary)
Impulse - The area under the overpressure-time curve for explosions.
The area can be calculated for the positive phase or negative phase of
the blast. (CCPS Glossary)
Deflagration - A combustion that propagates by heat and mass transfer
through the un-reacted medium at a velocity less than the speed of
sound. (CCPS Glossary)
Detonation - A release of energy caused by the propagation of a
chemical reaction in which the reaction front advances into the
unreacted substance at greater than sonic velocity in the unreacted
material. (CCPS Glossary)
Physical explosions are caused by the rapid release of mechanical energy, and include vessel
ruptures, BLEVEs and rapid phase transition. A vessel rupture occurs when the internal
pressure exceeds the mechanical strength of the vessel. The vessel strength is sometimes
weakened due to a material defect or corrosio n. A rapid phase transition can occur when a
material is exposed to a heat source. This in creases the material’s volume, increasing the
pressure in the container. Figure 4.14 summarizes the various explosion types and
terminology. It is possible for several to occur with any incident. |
Table A.3 IST Checklist Moderate Questions
3 MODERATE Questions:
3.1 Is it possible to limit the supply pressure of (hazardous) raw
materials to less than the maximu m allowable working pressure of
the vessels to which they are delivered?
3.2 Is it possible to make reaction conditions (for hazardous reactants
or products) (temperature, pressure) less severe by using a catalyst, or a better catalyst (e.g., structured or monolithic vs.
packed-bed)?
3.3 Can the process be operated at less severe conditions (for hazardous reactants or products) by considering:
• Improved thermodynamics or kinetics to reduce operating
temperatures or pressures
• Changes in reaction phase (e.g., liquid/liquid, gas/liquid, or
gas/gas)
• Changes in the order in which raw materials are added
• Raw material recycle to compensate for reduced yield or
conversion
• Operating at lower pressure to limit potential release rate
• Operating at lower temperature to prevent runaway reactions or
material failure
3.4 Is it possible to use less concentrated hazardous raw materials to reduce the hazard potential?
• Aqueous ammonia and/or HCl instead of anhydrous
• Sulfuric acid instead of oleum
• Dilute nitric acid instead of concentrated fuming nitric acid
• Wet benzoyl peroxide instead of dry
3.5 Is it possible to use larger partic le size/reduced dust forming solids
to minimize potential for dust explosions?
3.6 Are all process materials (e.g., he ating/cooling media) compatible
with process materials in event of inadvertent contamination (e.g., due to a tank coil or heat exchanger tube failure)?
3.7 Is it possible to add an ingredie nt to volatile hazardous materials
that will reduce its vapor pressure? 447 |
16. Task planning and error assessment 181
A resilient and methodical approach to task planning
The production of work instructions can be a high frequency and knowledge-
based activity during which mistakes may occur. The identification of task-specific
risks and safety requirements draws on knowledge of the process, process
hazards, and safety procedures. Task planning needs to be methodical and
account for all relevant hazards. If task planning is not done well, hazards may be
ignored or overlooked, safety procedures may be incomplete, and instructions can
be unclear. The people that are planning the tasks must be competent, and the
system of task planning should be resilient.
Optimism bias in task planning
Tasks often have completion deadlines. Ad ditional pressures include restoring
production quickly. This can contribute to “optimism bias” within task planning, for
example, being overly optimistic about how long a task will take. It can also involve
downplaying the challenges and risks in performing a task. This can contribute to
insufficient time being scheduled for a task and insufficient preparation of the
team.
Including error assessme nt in task planning
Many tasks are complex, with many task
steps. These tasks can occur over many hours,
they may involve many people, and they may
involve work in physically separate locations.
There may be unanticipated events (such as
equipment failure) that may increase task
complexity and require a change of plans. These
conditions create increased variability and the
need for operators to adapt, creating the
potential for errors and mistakes.
In addition, motivated staff can be very “task focused” and intent on completing
the task and solving the problems. This can create a risk of losing awareness of the
situation, improvising unsafe ways of completing a task, and overlooking
unexpected events or conditions that re quire a change in their actions. When
people are task focused, they can miss “weak signals” around them that the
situation is unsafe or is changing.
Task planning should:
•Identify the potential
for error
•Identify the means to
support a successful
task performance |
Chapter No.: 1 Title Name: Toghraei c15.indd
Comp. by: ISAKIAMMAL Date: 25 Feb 2019 Time: 12:30:36 PM Stage: Proof WorkFlow: CSW Page Number: 293
293
Piping and Instrumentation Diagram Development, First Edition. Moe Toghraei.
© 2019 John Wiley & Sons, Inc. Published 2019 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/Toghraei_PID
15.1 Introduction
What is the “plant control system, ” and how we can
implement it?
In more technical terms, how can we implement a
BPCS (basic process control system) in a plant?
A BPCS, or regulatory control system, can be divided
into two main levels in plants:
1) Pl
ant‐wide control. This is used to provide overall
control for the entire plant. Some people refer to
this as “heat and material balance control, ” since its primary role is to ensure that the plant produces the product in the predicted quantity and with the predicted quality. This control basically creates a link between a plant and its H&MB (heat and mass balance) table. Not all processes and unit operations are individually and directly connected to the plant‐wide control system.
2)
Equipment c
ontrol (unit operation control). Each
“unit” within the process may need to be controlled via its own BPCS with corresponding control loop(s). Most pieces of equipment don’t have an operating “point”; rather, they have an operating “window” . This is not necessarily because of an inherent weak -
ness of the equipment; this is something we like and gives the equipment the capability to “fluctuate” under different process conditions. The main duty of the unit control is to bring the unit to its optimum point within its operating window in each different set of process conditions.
It is important to mention that the classification of
the BPCS control into two levels is only based on their concepts; generally there is no difference in control hardware in a plant, and these two groups cannot be recognized or differentiated in P&IDs.
Each of the above concepts carries one aspect of plant
control. Plant‐wide control assures the “attachment” of the plant to its capacity and the quality of product(s), whereas equipment‐level control tries to bring a piece of equipment to its best operating point within its operating window and also protect the equipment at its weak points.
While in a P&ID all control systems can be traced, a
PFD generally shows only plant‐wide control. However, some P&IDs show some major elements of equipment‐level control too.
Plant‐wide control is discussed in Sections 15.2–15.4
of this chapter while equipment‐wise control will be discussed in Section 15.5 and after.
15.2 Plant‐Wide Control
There are two purposes to installing plant‐wide control:
1) The main pur
pose is to link the plant to its heat and
material balance table.
2) The s
econd purpose is surge or disturbance
management.
15.3 Heat and Mass Balance Control
The first purpose of plant‐wide control is heat and mate-
rial control.
Some people may prefer using the phrase of “mass
balance” or “material balance” control (rather than “heat and material balance control”). Their logic is: “in plants, we care about flow rate and quality of the product(s); no one is looking for a specific product with a specific temperature. ” While their logic is true in the majority of cases, it should be noted that to have a product with a specific quality, it may need to go through different steps of operation, which need
spe
cific operating temperatures. Therefore, “heat con-
trol” is still needed.
In order to ensure this, theoretically we must have
at least one flow control loop and one composition control loop with a manual set point that comes from the H&MB table.15
Plant Process Control |
KEY RELEVANCE TO PROCESS PLANT OPERATIONS 39
Example Incident 3.3 – BP Texas City 2005 – ( cont.)
Lessons learned in relation to abnormal situation management:
Operating procedures: This event happened during a transient
operation when starting up the column. The startup procedure
was not correctly followed, although the US Chemical Safety
and Hazard Investigation Board (CSB) subsequently found that
procedural deviations during startup had become common
practice. (CSB 2007)
Management of Change: Operating practices changed over
time to reflect difficult control of startup, but management
failed to address the safety im plications of these changes and
procedures were not updated.
Process Monitoring and Control:
o The process was allowed to operate outside normal
limits for both the column bottom level and the
temperature. Critical alarms were out of commission. A
lack of situational awaren ess by the control panel
operators resulted in no attempt to bring the column
back into safe operating limits during the incident.
o Providing suitable informat ion and system interfaces
for front line staff enables them to reliably detect,
diagnose, and respond to potential incidents. The HMI
should be designed so that the operator has multiple
ways of viewing plant status, improving situational
awareness that would make it easier to identify level
gauge failure.
Organizational roles and work processes: Personnel response
to the incident was inadequate and lacked supervisory
intervention. Shift handover documentation was insufficient to
help incoming operators understand the gravity of the
situation. Safety culture was poor.
Work Environment: Inadequate definition of appropriate
workload, staffing levels, and working conditions for front line
personnel. |
Table 21-2 continued
Human
performance tool
(HPT) Description Usage
Dynamic Risk
Assessment
Stop-Think-Act-Review (STAR) assessment is often part of a Dynamic Risk
assessment. Following is a description of the S-T-A-R steps:
Stop
• Look for hazards
• Review hazards
• Has the situation changed?
Think
• Evaluate the situation
• Evaluate options
Act
• Apply safety measures
• Recommence the work
Review
• Complete an after Action Review
• Reassess the system of work
• Record lessons learned for sharing When operating in
skill-based and rule-
based performance
modes.
Particularly effective
for repetitive tasks.
STOP
Act
now |
11. Inherent Safety & the Elements of a RBPS
Program
Chapter 11 will describe the relation ship between the four main IS
strategies, i.e., Substitution , Minimization , Moderation , and Simplification
and each element of a PSM/RBPS pr ogram. The possible use of the IS
strategies in carrying-out the activities of the elements will be described.
The interrelationship between inhere nt safety and PSM programs has
been previously described by Kletz and Amyotte (Ref 11.16 Kletz 2010)
and Amyotte, Hendershot, et al (Ref 11.5 Amyotte) and their conclusions
are summarized herein. Amyotte & Klet z argue that inherent safety is
implicitly part of PSM/RBPS programs, that it not be included as a
discrete element, but as part of th e thought process for the design of
these programs and how they are a pplied and implemented. In their
book and in this chapter more explicit applications of the IS strategies
are proposed (Ref 11.16 Kletz 2010). For some PSM/RBPS elements the
relationship with the IS strategies is direct and relatively strong, e.g., PHA,
whereas for other elements the rela tionship is more indirect, e.g.,
Measurement and Metrics.
The four IS strategies are usually applied in the context of the
chemicals and the hazards/ risks that they present, e.g., substituting one
chemical with another that presents less of a process safety hazard, or
minimizing the inventories of the chemicals that can create process
safety hazards. Traditionally, IS has b een regarded as an intrinsic part of
the design of the process, i.e., part of the “hardware” aspect of the
process or as part of the properties of the process with respect to the
hazards presented by the hazardous ma terials used in the process. In
this chapter, the application of the same thought processes of IS can be
applied to aspects of the process that are largely programmatic, i.e., the
design and execution of the PSM/RBPS program policies, practices, and
procedures. This is a new applicat ion of IS concepts. For example,
Minimization has traditionally been asso ciated with reducing the
inventory of hazardous materials, wh ich is a physical aspect of the
process. However, we can pose the question: Can/should shift schedules
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294 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
The experiment is repeated for different do ses and Gaussian curves are drawn for each
dose. The mean response and standard deviation are determined at each dose. A complete
dose-response curve is produced by plotting th e cumulative mean response at each dose. For
convenience, the response is plotted versus the logarithm of the dose. The logarithm form
arises because in most organisms some subjects can tolerate high levels of exposure while
others are sensitive. Simpler forms of dose response are useful for emergency response
planning and these use a standard time of exposure (30 or 60 minutes) and provide different
levels of impact from mild impact to serious injury (e.g. ERPG discussed in Section 13.7.2).
For most engineering computations, an equati on is more useful than the dose-response
curve. For single exposures, the probit (proba bility unit) method provides a transformation
method to convert the dose-response curve into a straight line. Probit equations are available
for a variety of exposures, including exposures to toxic materials, heat, pressure, radiation,
and impact. For toxic exposures, the causative variable is based on the concentration; for
explosions, the causative variable is based on the explosive overpressure or impulse, ,
depending on the type of injury or damage. For fire exposure, the causative variable is based
on the duration and intensity of the radiative exposure. The probit method is generally the
preferred method of choice for consequence analys is studies. A limitation is the restricted set
of chemicals for which probit coefficients are published.
Toxic Outcomes
Toxic impact models are employed to assess the consequences to human health as a result of
exposure to a known concentration of toxic ga s for a known period of time. For consequence
analysis, the toxic effects are due to short-term exposures, primarily due to vapors. Chronic
exposures are not considered here. Many releas es involve several chemical components or
multiple effects. The cumulative effects of simu ltaneous exposure to more than one material
are not well understood.
Predictions of gas cloud concentrations and du rations at specific locations are available
from neutral and dense gas dispersion models.
Toxic concentration criteria and methods incl ude the following which were discussed in
Chapter 6.
Emergency Response Planning Guidelines fo r Air Contaminants (ERPGs) issued by
the American Industrial Hygiene Association (AIHA)
Acute Exposure Guideline Levels (AEGL) ma intained by the U.S. EPA in cooperation
with the National Academies. (EPA AEGL)
Immediately Dangerous to Life or Health (IDLH) levels established by the National
Institute for Occupational Safety and Health (NIOSH)
Emergency Exposure Guidance Levels (EEGLS) and Short-Term Public Emergency
Guidance Levels (SPEGLs) issued by th e National Academy of Sciences/National
Research Council (NAS)
Probit Functions |
378 INVESTIGATING PROCESS SAFETY INCIDENTS
was set below the current normal batch level. The batch size had been
changed from a 70% level to an 85% level but the alarm was still set for
80%; as a result, the batch level alarm was going off each time Kettle No. 3
was filled to the new normal batch level. (Management of Change, Conduct of
Operations)
viii Absence of Redundant Protection
There was no redundant back-up protec tion (second level or monitoring of
the pump) to shut down the pump in case it was blocked in. The hazard
i d e n t i f i c a t i o n & r i s k a n a l y s i s ( H I R A ) for the raw material storage, catalyst
preparation, and catalyst storage areas was up for renewal this year. The prior
HIRA was not as thorough as expected by today’s standards. The corporation
has now established criter ia for HIRA leaders and has an approved list of
resources. (Hazard Identification & Risk Analysis, Engineering Design)
N ote: The isopentane feed valve is designed to fail closed on power
failure, to prevent reverse flow from th e kettles to the raw material storage
tanks. This is the appropriate failure position for this valve.
Other Causal Factors:
Other causal factors were related to possible improvements in emergency
planning and response, as follows:
ix Fire Brigade Procedures
No fire brigade member reported to the fire pump house when the
fire alarm sounded. Interviews sugges t personnel were confused about
whose responsibility it was to go to the fire pump house. This may be a training or drill issue. (Emergency Management)
x Understanding of Fire Hazards The fire brigade approached the cata lyst preparation area to attempt
rescue of a victim while firewater was unavailable. The small amount of
water available on the fire engine wa s enough to protect the rescuers from
the radiant heat from the fire, bu t was no protection against metal
fragments. While the fire brigade did not recognize the potential hazards of
this incident, further invest igation is needed to determine if the emergency
responders received insufficient training or if the emergency response plan
is deficient in this area. (Emergency Management)
xi Personnel Headcount Procedures
The presence of the contractor (wor king in the instrument house) was
not known to unit personnel. The contractor works in the area routinely,
sometimes in the instrument house and sometimes in the rack. Because
the instrument house is a general purpose area, a permit is not required |
Piping and Instrumentation Diagram Development
180
All the systems on the minimum flow protection pipe
could be replaced with a device named an automatic
recirculation valve or ARC. It looks very attempting to use a single device such as ARC instead of the more complicated, utility dependent control system. However, ARCs have some shortcomings. First of all they are very prone to plugging if the service liquid is not clean. The other limitation is that ARCs are not available in large sizes, possibly larger than 6″. Inside ARCs are a bypass valve and a spring‐loaded check valve. The P&ID symbol for an ARC is very similar to a check valve but the differ -
ence is that the ARC symbol has two outgoing lines (Figure 10.12).
It is important to know that not all loops around the
pumps in the P&ID are “minimum flow protection pipes, ” there could be similar pipes in the P&ID or plants for some other reasons. A loop around the pump could be implemented on a pump for the following reasons:
●As a minimum flow protection pipe.
●To protect the pump from gradual heating during dead head conditions (mainly for flammable liquids).
●To provide fluid moving around the pump to maintain the flow during electrical outages where the pump is supplied by emergency electricity.
●To achieve an acceptable efficiency in very small cen-trifugal pumps (less than 10 m
3 h−1).
●To providing a start‐up pipe for positive displacement pumps.
If this loop around a pump is implemented for each of
above reasons, they should be sized based on different criteria.
10.6.3
C
avitation
Cavitation is a phenomenon that is related to the genera-
tion and collapse of vapor bubbles inside of pumps.
When this happens, the pump fails prematurely
because of bubbles slamming into the impellor and the internal side of the casing. The collective name for these events is cavitation.
The main underlying reason for cavitation is a lack of
enough pressure on the suction side of a centrifugal pump. When a centrifugal pump operates, it basically “sucks” the liquid, which can generate bubbles on its suction side, causing cavitation.Have you tried to suck a carbonated drink out of a
tall bottle with a narrow straw? You might notice a bunch of bubbles coming into your mouth. However, luckily cavitation won’t happen in your mouth because bubbles don’t have much speed!
If the liquid on the suction side of a centrifugal pump
has “enough” pressure, it won’t release gas and cavitation won’t happen. The problem of a “lack of enough pressure on the suction side of a centrifugal pump” can be stated more technically as: a “lack of enough NPSH. ”
NPSH or “net positive suction head” is basically the
total “effective” pressure of a liquid at the suction flange of a centrifugal pump in “head” units (e.g. meters or feet).
Each centrifugal pump has a minimum acceptable
NPSH, which is reported by the pump manufacturer and is termed the “required NPSH, ” or net positive suction head required (NPSH
R).
A typical NPSH R for a centrifugal pump could be
a value anywhere from less than a meter, up to more than 10 m.
After buying a centrifugal pump, the process and the
control system should be designed in order to ensure that the liquid has enough pressure at the suction flange to prevent cavitation. This pressure, which is provided by the system (rather than the pump), is termed “avail-able NPSH, ” or net positive suction head available (NPSH
A), and is reported in the same units as head (e.g.
meters or feet).
This concept is shown in Table 10.7.NPSH
A should be higher than NPSH R by a pre‐selected
margin, otherwise the centrifugal pump will most likely cavitate.
The service fluid type is part of the “system” too.
Where the pumping fluid is hotter or more volatile the pump is more prone to cavitation.
There are, however, cases where NPSH
A is lower than
“NPSH R + margin. ” There different techniques available
to solve the problem. To apply some of the solutions the designer should go back to the design stage of project but for some others, some changes during the P&ID devel-opment could solve the problem.
Each of the items in Table 10.8 need detailed evalua-
tion by process engineers and other stakeholders to check their applicability.
A “stand pipe, ” which is a solution to increase NPSH
A,
is a simple vertical vessel that accumulates the liquid to a higher level for the benefit of the downstream centrifugal pump. The dimension of a standpipe is decided and these rules of thumb can be used. The diameter is prefer -
able less than 24″ to be able to use a piece of pipe (seam-less) as the body of the standpipe. The height is primarily defined by the required level of liquid in it to provide enough NPSH
A. It is generally preferable to leave the
top of the standpipe open to atmosphere to get rid of Figure 10.12 Minimum flo w protection pipe with an automatic
recirculation valve. |
34 PROCESS SAFETY IN UPSTREAM OIL & GAS
commencing in 1992. This was based extensively on API RP 750. This applies
mainly to downstream refining, chemical and petrochemical plants. It also covers
some upstream facilities, such as large on shore treatment facilities and gas plants,
but not well construction. Coverage is based on threshold amounts of nominated
hazardous chemicals. Other in cidents, including Bhopal in 1984 (Less, 2012), led
the EPA to issue the Risk Management Plan Regulations, which are similar to PSM,
but with a focus on offsite impacts. As we ll as a formal process safety management
system, the EPA requires that the facility car ry out an offsite consequence analysis
to predict worst case hazard zones and to repo rt on 5-year incident histories. This
regulation also applies to larger scale upstream treatment plants based on their
maximum inventory, similar to OSHA PSM.
In the prescriptive approach, the company and the regulator determine, by a
review of documents or by inspection, whether the regulatory requirement has been
implemented. This process ensures that go od solutions are adopted. It does require
that the regulator or industry body develops and keeps up to date the required
solutions. Maintaining current solutions is demanding in industries such as
deepwater offshore, which have complex and changing designs. A potential issue
with prescriptive requirements is that once the remedy is implemented, then a culture
of compliance may develop and not consider other solutions, even if they could
potentially provide additional risk reduction.
The EU approach for downstream is goal-based. Two downstream major
incidents occurred in Europe in the 1970s (Flixborough and Seveso) and these along
with the Bhopal incident in 1984 (all described in Lees, 2012 and CCPS, 2008b)
resulted in the EU developing the Seveso Directive, a goal-based process safety
regulation. A summary of the current requirements is provided on the UK HSE
website (see references). This requires a formal process safety management system
and a risk assessment as part of a safety case document. In the goal-based approach
the process safety objective is defined, but the actual solution is left to the company.
The safety objective is often ALARP – As Low As Reasonably Practicable. For
ALARP, additional safety measures to reduce risk should be assessed and
implemented so long as the measure is practical, considering trouble, time, and
money. The company must demonstrate to th e regulator that the solution adopted is
adequate for the potential risk.
In the upstream domain, the Piper Alpha di saster in the UK sector of the North
Sea in 1988 resulted in 167 fatalities (IChemE, 2018 and Oil & Gas UK, 2013). The
subsequent Cullen Inquiry (HSE, 1990) recommended, amongst other things, a
safety case approach for offshore. This re quires a safety case or for floating drill
rigs, an IADC-style HSE Case. The safety case includes a facility description, major
hazards identification and risk assessment, the process safety and environmental
management system, the technical solutions (addressing key barriers – their
performance standards, how they are maintained, and verification), and the
emergency response actions/procedures. The UK regulations are implemented in a
family of regulations led by safety case which is goal-based but including more |
131
At one plant, operators were required to monitor a bulk solids
railcar unloading operation. The pneumatic blower and
hydraulic vibrator used for the task created a very high noise
area around the railcar, requirin g the operator to wear both
earplugs and earmuffs as they monitored the unloading
operation. It became common practice to “monitor” from farther and farther away from the railcar (to escape the noise), at a
d i s t a n c e w e l l i n e x c e s s o f t h e regulatory requirements. An
operator’s shed was installed with very effective sound insulation, which (along with the necessary air conditioner!)
allowed the operators to closely monitor the process in comfort
and safety.
A facility which manufactures rock et propellant designed their
processing building (in which the propellant was formulated and
mixed) with large earthen berms surrounding the building, to absorb the force of any explosions.
7.5 MORE ROBUST PROCESS EQUIPMENT AND DESIGN
In parallel with the concept of inherently robust equipment design
introduced in Chapter 6, in whic h losses of containment were made
virtually impossible, applying the substitution strategy, by using more
robust materials of construction or more robust designs can reduce the
likelihood of system or component failure, consequently reducing the
likelihood of losses of containment, toxic releases, fires, and explosions.
In previous examples, higher alloy materials of construction have been shown to provide better corrosion resistance but can also provide increased toughness and fatigue resistance. Improved casing designs for rotating equipment can reduce the likelihood of losses of primary
containment in the event of rotating element failure. Pump designs with double mechanical seals are more robu st than single se al pumps. Seal-
less pumps greatly reduce the risk of a process fluid leak, but they also
introduce new hazards and concerns, such as overheating and internal leakage, which may be very rapi d. Newer seal-less pump designs
incorporate advanced thermal protecti on shutdown devices to prevent
overheating. Other more robust pump designs, depending on the
application, include diaphragm pu mps, jet pumps, and eductors. Using
smart transmitters instead of older analog transmitters in a given application make the contro l function more reliable. |
262 Human Factors Handbook
21.3 Practical situation awareness tools and tactics
Given the importance of situation awareness in many safety critical tasks, advice
can be offered on how to minimize the risks of reduced situation awareness.
Human performance tools are useful and can be used to reduce human error and lead to various positive outcomes, such as:
• Heightened sense of situation awareness concerning safety, presence of
error precursors and error traps, task s to be performed, conditions, and
surroundings.
• More accurate estimates of risk level of activities.
• Higher level of self-awareness, including biases, vulnerabilities, deficiencies, and limitations.
• The most commonly used human performance tools are shown in Table
21-2.
These tools can also help foster agile thinking. For example, the Dynamic Risk
Assessment includes reviewing the effect of actions and adapting these. |
100 GUIDELINES FOR MANAGING ABNORMAL SITUATIONS
4.2.6 Environmental Health, Safe ty and Security (EHSS)
Personnel
EHSS personnel are more likely to act as responders to the consequences
of abnormal situations that have developed into a loss of primary
containment. Events that are more significant typically require a response
by emergency teams with outside in dustry assistance and external
responding agencies.
4.2.7 Technical Experts
Technical experts, also called “subject matter experts” (SMEs) are often
located remote from the facility but could be called upon to help to
diagnose or respond to an abnormal situation (as discussed in
Example Incident 4.5). While it is not possible to consider the whole range
of technical expertise that may be involved in such a situation, these
individuals could include:
Instrument engineer, to explain how a level gauge may not respond
to a change in level.
Rotating equipment specialist, to help diagnose why a compressor
starts to vibrate under abnormal conditions or the rotating
equipment vibration profile has changed over time.
Quality control engineers/specialists to help troubleshoot
contamination and composition of raw and process chemicals.
Materials engineer, to help understand the significance of a minor
crack that appears in a flange on a pressure vessel.
Piping engineer to evaluate the risk associated with the movement
of a pipe support.
Technology Licensors to provide sp ecific expertise related to the
process.
|
Piping and Instrumentation Diagram Development
376
User User UserUserFigure 17.22 Distribution and c ollection network of
a utility.
User User UserUserFigure 17.23 Connec ting pipe between
distribution and collection networks.
DPC Figure 17.24 Connec tion between distribution and
collection networks.
Steam NPSsCond. line
Steam line
T
NPSc
CondensateTFigure 17.25 Connec tion between
steam and condensate networks. |
PROCESS SAFETY AND MANAGEMENT OF ABNORMAL SITUATIONS 21
Example Incident 2.3 – Texaco Refinery, Milford Haven ( cont. )
Operators missed key information, such as the buildup of liquid
in the KO drum, which could have prevented the explosion.
However, a previous modification that involved the removal of
the automatic pump-out system limited their options.
For several hours after the light ning struck, operators were
overwhelmed by a flood of 2040 alar ms (at an estimated rate of
one every two to three seconds), all of which were designated
‘high’ priority. Many were only informative, but the existing alarm
design did not separately prioritize and display safety-critical
alarms. Alarms were annunciate d faster than the operators
could recognize, acknowledge, and respond to them, including
275 alarms in the final 11 minutes prior to the explosion.
Lessons Learned in relation to abnormal situations:
1) For management / engineers:
Relief systems should be designed to handle worst-case
abnormal situations.
Safety critical alarms should be distinguishable from other
operational alarms.
The number of alarms should be limited to allow effective
monitoring by operators. A “fir st-out” alarm system can be a
useful design feature in these circumstances. See Chapter 5 on
tools and methods.
Control panel graphics should include a process overview screen
to help with troubleshooting.
Modifications (removal of pump-out system) should consider
abnormal situations.
A plant safety system must be robust enough to handle
situations where a human response to an alarm is not enough to
mitigate the issue.
|
2.10 Lear n to Assess and Advance the Culture |69
that constantly refreshes itself. The following paragraphs suggest
som e ways to learn and advance the culture.
B e adaptable
Adaptable organizations continually adopt new and improved
ways to do work, and the different units or groups in these
organizations often cooperate to create change. Adaptable
organizations also demonstrate a strong user/customer focus.
This focus on change and improvem ent can also be directed
to improving culture. However, without careful review of
proposed changes, being adaptable can lead to norm alization
of deviance. Therefore, culture im provement efforts should be
accompanied with careful review. The organization should
define and understand its boundaries of acceptable process
safety perform ance. Any variation should keep within these
boundaries (Ref 2.3).
B e competent Each person whose job addresses process safety in some way
should possess the required knowledge and skills to perform
this position (Ref 2.33). Clearly, process safety experts need to
be competent in their disciplines, but competence does not
end there. Process safety com petence applies to everyone in
the facility. Design engineers should be com petent in
applicable standards. Decision-m akers should understand
how to interpret risk assessment data. Operators and
m echanics should be able to perform all required tasks and
understand the importance of following procedures. Leaders
should understand and be able to build process safety culture.
B e aware All facility personnel should support the process safety
program, whether they have a formal process safety role or
not. Each person on the site should be thoroughly |
12.8 Embed and Refresh | 167
12.8 Embed and Refresh
Three years had passed since Frederik, Pamela, Alexandre, and Reed came up
with a plan to address the minor tank overflows. At Reed’s retirement party,
Jan said, “First, I want to thank Reed for all his years of service with us. He has
been such an important part of our work family. We might not have resolved
the overflow incidents a few years ago without his diligence and hard work.
We will most certainly miss him.” “Hear, hear!” the crowd cheered. Jan
continued, “Second, I’m pleased to announce that we will embark on a new
adventure, one that will modernize our terminals. We will put into motion a
project to upgrade our tank measuring system with radar technology.
Everybody will be critical to the success of this project, and that includes all the
new folks, as well as the more seasoned ones, like myself.”
Frederik, Pamela, Alexandre, and Reed looked at each and smiled. The
plan they had put together three years ago was finally coming to fruition.
Alexandre, who Pamela considered her protégé, was going to lead the
project. “When I retire, I’ll be leaving the department in Alexandre’s capable
hands,” Pamela thought with satisfaction.
12.9 References
If so indicated when each incident described in this section was introduced,
the incident has been included in the Index of Publicly Evaluated Incidents,
presented in the Appendix.
Other references are listed below.
12.1 Ilyushina, M. (2020). Putin declares emergency over 20,000-ton diesel
spill. CNN (4 June 2020). |
36 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
Figure 3.1. Lac-Megantic tank cars with breaches to their shells
(TSB 2013)
Detailed Description
The MMA-002 train was traveling from North Dako ta to a refinery in New Brunswick, Canada.
The train was made up of 72 cars carrying 7. 7 million liters (2 million gallons) of crude oil
(UN1267). Just before midnight on July 5, 2013, the train was parked in Nantes, Quebec,
Canada.
The 1,433 m (4,700 ft) long train that contained 72 tank cars loaded with crude oil from the
Bakken fields in North Dakota. (NTSB 2015) The cars were DOT-111 design. With the fracked
crude from primarily Texas and North Dakota, th e U.S. was producing more crude oil than it
had in 30 years. Transportation of crude oil by rail had increased significantly to move the
crude to refineries for processing. Carloads carrying oil in 2014 rose by more than 5000
percent when compared with 2008 numbers (NCSL 2015).
The fracked crude oils from fo rmations such as the Bakken tend to be lighter than other
crudes. They are of a lower density, flow fr eely at room temperature, and have a higher
proportion of light hydrocarbon fractions result ing in higher API gravities (between 37° and
42°). A Sandia report stated that “No single pa rameter defines the degree of flammability of a
fuel; rather, multiple parameters are relevant .” (Sandia 2015) The attention following this
incident is continuing to prompt discussion on the safe transport of various classifications of
crude oils.
The locomotive engineer stopped the train on a downhill grade on the main track. He used
the pneumatic brakes, applied the brakes on the locomotive and the buffer car, and began to
apply the hand brakes to some cars (but fe wer than recommended in company procedures),
and shut down the trailing locomotives. He test ed the hand brake by releasing the locomotive
automatic brakes but did not release the locomotive independent brakes.
He communicated with the rail traffic controller noting mechanical difficulties he had
experienced including excess smoke and a loss of power in the lead engine. They decided to
address these issues in the morning. The locomoti ve engineer went off-duty to stay in a Lac-
|
GLOSSARY 419
qualitative techniques to pinpoi nt weaknesses in the design and
operation of facilities that could lead to incidents.
Hazard Identification and Risk Analysis (HIRA) — A collective term that
encompasses all activities involved in identifying hazard s and evaluating
risk at facilities, throughout their life cycle, to make certain that risks to
employees, the public, or the enviro nment are consistently controlled
within the organization's risk tolerance.
High Potential Incident —An event that, under different circumstances,
might easily have resulted in a catastrophic loss.
Historic Incident Data —Data collected and recorded from past incidents.
Human Error —Intended or unintended human action or in action that
produces an inappropriate result . Includes actions by designers,
operators, engineers, or managers that may contribute to or result in
accidents.
Human Factors —A discipline concerned wi th designing machines,
operations, and work environmen ts so that they match human
capabilities, limitations, and needs . Includes any technical work
(engineering, procedure writing, worker training, worker selection, etc.)
related to the human factor in operator-machine systems.
Human Reliability Analysis —A method used to evaluate whether system-
required human-actions, tasks, or jo bs will be completed successfully
within a required time period. Also used to determine the probability that no extraneous human actions detrimental to the system will be
performed.
Hypothesis —A supposition or proposed explanation made on the basis of
limited evidence as a starting point for further investigation.
Impact —A measure of the ultimate loss and harm of a loss event. Impact
may be expressed in terms of numbers of injuries and/or fatalities, extent
of environmental damage and/or magnitude of losses such as property damage, material loss, lost producti on, market share loss, and recovery
costs.
Incident —An unusual, unplanned, or unex pected occurrence that either
resulted in, or had the potential to result in a process upset with potential process condition excursions beyond operating limits, release
of energy or materials, challenges to a protective barrier, or loss of stakeholder confidence in a company’s reputation.
Incident Investigation —A systematic approach fo r determining the causes
of an incident and developing recomme ndations that a ddress the causes |
APPLICATION OF PROCESS SAFETY TO ONSHORE PRODUCTION 91
5.2 ONSHORE PRODUCTION FACI LITIES: RISKS AND KEY
PROCESS SAFETY MEASURES
The identification processes for risks are generally one of the first activities carried
out. The actual processes used are summarized later in Section 5.3.2.
5.2.1 Leak from Production Facilities
Risks
There are multiple potential leak sources at upstream gas plant facilities, where most
of the production is carried out at modera tely high pressures that typically exceed
1000 psi (69 bar). This means that even small holes can cause large leak rates.
Typical leak sources include pipes, flan ges, small bore connections, compressor and
pump seals, and vessels. Corrosion is often a contributory cause as well fluids
contain water and acid gases. Other causes include vibration from compression
activity, erosion from sand in the oil, impacts from work activities, or design or
construction defects (e.g., in correct gasket materials).
A leak of flammable materials can lead to jet fires and/or pool fires. If a vapor
cloud forms and is subsequently ignited, a flash fire occurs. If sufficient congestion
exists, the flash fire flame can accelerate and cause a vapor cloud explosion. Means
to estimate potential outcome hazard zones are provided in the Guidelines for
Chemical Process Quantitative Risk Analysis (CCPS, 1999). The actual outcome for
a leak depends on the initial condition and how the event progresses. This is shown
in Figure 5-2 from IChemE (1996). This is complex and not easy to execute using
manual techniques and most companies us e specialized consequence software.
As mentioned previously, some onshore production facilities are located inside
large buildings, for example on the North Slope of Alaska or North Africa, which
allows operators and maintenance personnel to work in a temperate environment
which enhances process sa fety. A downside to locating large facilities inside
buildings is that leak events, which safely disperse with the wind if outside, can
more easily create flammable clouds inside . This increases the potential for flash
fires or vapor cloud explosions in conge sted spaces (see box Vapor Cloud Explosion
– Short Primer in Section 5.3.2). This h azard is managed by preventing leaks (e.g.,
mechanical integrity program) or mitigating them if they occur through the provision
of gas leak detection with ESD and a more extensive fire detection and suppression
system than is typically used in outside locations.
Sour gas fields contain H 2S and organic sulfur compounds. In the US, H 2S
concentrations are usually less than 4%, but are much higher in wells in several
states (e.g., East Texas, Colorado, and Wyoming). In the Middle East, some fields
are 50% H 2S. A leak of produced gas at 4% (40,000 ppm) H 2S is a serious toxic
hazard as the ERPG-3 is 100 ppm (the conc entration that most people can survive a
1 hour exposure) and concentrations above 500-1000 ppm can be rapidly fatal. This
is mitigated to some degree if the vapor produced is buoyant (i.e., dominated by
methane content) that tends to disperse any leak upwards, away from ground level.
However, natural gas with significant C 3+ and H 2S can be a dense gas and not |
xxviii PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
RP Recommended Practice
SACHE Safety and Chemical Engineering Education
SCAI Safety Controls Alarms and Interlocks
SDS Safety Data Sheet
SHIB Safety Hazard Information Bulletin
SIF Safety Instrumented Function
SIL Safety Integrity Level (a s per IEC 61508 / 61511 standards)
SIS Safety Instrumented System
SOL Safe Operating Limits
TEEL Temporary Emergency Exposure Limit
THERP Technique for Human Error Rate Prediction
TQ Threshold Quantity
UFL Upper Flammable Limit
U.K. United Kingdom
U.S. United States
UST Underground Storage Tank
VCE Vapor Cloud Explosion
|
Figure 15-5: Guidelines on shift design
|
TOOLS AND METHODS FOR MANAGING ABNORMAL SITUATIONS 149
Where possible, learning should be embedded into the operation
through hardware, software, or procedur al changes. It is not always easy
to identify the occurrence of an abno rmal event, but this can be helped
by having a good reporting culture, perhaps assisted by a system of
automated metrics reporting as described in Chapter 6.
The tools for investigating and lear ning from incidents are available
in recognized and available publicatio ns. Therefore, rather than discuss
them in this book, some suggested CCPS published reference books on
Incident Investigations, Metrics, and Bow Ties are:
Guidelines for Investigating Process Safety Incidents , 3rd edition 2019
(CCPS 2019)
Guidelines for Integrating Manageme nt Systems and Metrics to Improve
Process Safety Performance (CCPS 2016c)
Bow Ties in Risk Management (CCPS 2018a)
5.9 CHANGE MANAGEMENT
Changes to processes and organizati ons occur for several reasons such
as equipment upgrades or failures, process optimizations, design
changes, new products, and busin ess impacts. These changes may be
very positive when managed thorough ly but may have just the opposite
result if not actively managed and fu lly evaluated. Table 5.10 references
the management of change procedure for processes as well as
organizations.
|
•Simplification sometimes involves a tradeoff between the
complexity of an overall plan t and complexity within one
particular piece of equipment. For example, a reactive distillation
process for producing methyl acetate requires only three
columns and the associated support equipment. The older
process required a reactor, an extractor, and eight other
columns, along with the associat ed support equipment. The new
process is simpler, safer, an d more economical, but the
successful operation of the reac tive distillation component is
itself more complex and knowledge-intensive (KA).
•Redesigned latex reactor cleani ng equipment eliminates the
potential for incorrect installation that could result in unwanted
reactivity or cross contamination (OK).
•Dow eliminated the use of hoses in several hazardous services
in favor of hard piped connections (OK).
15.9 ADDITIONAL LITERATURE GIVING EXAMPLES OF INHERENTLY
SAFER OPERATIONS
•Amyotte, P.R., Goraya, A.U., Hendershot, D.C., and Khan, F.I. (2007). Incorporation of Inherent Safety principles in process
safety management. Process Safe ty Progress, 26 (4), 333-346.
•CCPS (1993). “Inherently Safer Plants.” Guidelines for Engineering
Design for Process Safety (Chapter 2). New York: American
Institute of Chemical Engineers.
•Commission of the European Comm unity (1997). INSIDE Project
and INSET Toolkit. Available for download at www.aeat-safety-and-risk.com/html/inset.html.
•Kletz, T.A. (1998). Process Plants - A Handbook for Inherently
Safer Design, London, UK: Taylor and Francis.
•“Layer of Protection Analysis and Inherently Safer Processes."
Process Safety Progress, 18, (4), 214-220, Winter 1999.
•'Inherently Safer Approaches to Plant Design', DP Mansfield, 430 |
Chapter No.: 1 Title Name: <TITLENAME> c09.indd
Comp. by: <USER> Date: 25 Feb 2019 Time: 12:23:39 PM Stage: <STAGE> WorkFlow: <WORKFLOW> Page Number: 143
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Piping and Instrumentation Diagram Development, First Edition. Moe Toghraei.
© 2019 John Wiley & Sons, Inc. Published 2019 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/Toghraei_PID
9.1 Introduction
One important duty of items in process plant is holding
and storing process material.
Process materials – for the purpose of holding or
storing – can be divided into four groups: flowable solids, non‐volatile liquids, volatile liquids, and gases/vapors. Each of these materials may need a specific type of container.
9.2 Selection of Containers
The volume of a stored material is also arbitrarily divided into four classes: low volume, medium volume, high volume, and very high volume.
As can be seen in Table 9.1, for each type of material, in
each class of storage, several options are available. Flowable solids can be simply stored in bags if they are of low volume. If the flowable solid is of medium volume, it could be stored in jumbo bag. And if the volume is high it can be stored in a silo. If the solid is not easily flowable and/or it is of huge volume, it can simply be stored in an open pit or on an open pad in the form of a stockpile. Storing in open pits or an open pad can be done only if the weather doesn’t destroy the solid.
For non‐volatile liquids (like water), if they are of low
volume they could be stored in tote tanks. Tote tanks are plastic or metallic tanks with a volume of about 1 m
3.
Some tote tanks have a volume of 1 m3, some others 1.5
or 1.8 m3. If a liquid of medium volume needs to be
stored it could be stored in tanks or vessels. If a non‐volatile liquid of high volume needs to be stored the only available option is a tank.
Storing large volume of volatile liquids is done only
through using floating roof tanks. A non‐volatile liquid can be stored in ponds or reservoirs, as long as it is safe to do so.
For storing volatile liquids, if their volume is low a vessel
is available. For medium volume there are two available options of tanks or vessels, and if the volume is high the only available option is a tank. For volatile liquids, if they are supposed to be stored in tanks, it could be a floating roof tank or a fixed tank with a blanketing gas system.
To store gas, vapor, or highly volatile liquids in low
volume a capsule is the available choice. Capsules are a type of vessel that are ended with spherical heads. If gas, vapor, or highly volatile liquid is of medium volume it can be stored in a vessel and if the volume is high a spheri-cal tank is the only option. Gas in very high volumes can be stored only in underground natural reservoirs.
In this chapter we mainly focus on tanks and vessels.
The word container can be used for all man‐made enclo-sures in classes of low, medium and high volume. Even though the terms “tank” and “vessel” are sometimes used interchangeably, they are in fact different. Generally, when we are talking about “vessels” it is a container with a high design pressure, while a “tank” refers to containers with a low design pressure, approximately atmospheric pressure. The distinction between low pressure and high pressure is subjective, but usually the division is 15 psig, meaning that if the design pressure of the container is higher than 15 psig it is considered a vessel (or better, a “pressure vessel”), and if the design pressure of a container is below 15 psig, then it is called a tank (or better, an “atmospheric tank”). However, generally the design pressure of tanks is less than 3 psig (approximately 20 kPag or 0.2 barg).
From the above explanation it can be realized that usu-
ally containers that have medium or high volume cannot be in the form of vessels, because vessels have a higher designed pressure and the thickness of their body is high. Therefore vessels cannot be built with high volumes economically. If a high volume container is built, it is more attractive from an economic point of view for it to be a tank, which has lower design pressure.
To store very high volumes of non‐volatile liquids,
ponds, or reservoirs can be used. The depth of ponds is generally limited to 4–5 m (Figure 9.1). A reservoir can be considered as larger and deeper versions of ponds. Reservoirs are common for storing water and it is best to use natural terrain as a reservoir so that minimum change and effort is required.9
Containers |
RISK MITIGATION 339
Detailed Description
The Celanese plant was built in 1952 and produced acetic acid. The unit involved was a liquid
phase oxidation (LPO) reactor in which butane was oxidized in the presence of air and a
catalyst to make acetic acid and byproducts. This was an ex othermic reaction. The reactor
product was sent to several downstream units in the Pampa plant to make products that
included acetic acid, acetic anhydride, and me thyl ethyl ketone. The reactor operated at a
relatively high temperature and pressure. Fi gure 15.3 is a schematic of the reactor.
On November 14, 1987, the reactor was prepared to start up following a shut down the
previous day due to a problem in the steam sy stem. Following the normal start-up process,
the operators began heating the reactor cont ents. As the reactor approached start-up
temperature, an explosion occurred in the ai r sparger inside the reactor. The explosion
ruptured the 200 mm (8 in) diameter air piping at two places external to the reactor and one
failure occurred internal to the reactor. The fl ammable reactor contents rapidly vaporized to
the atmosphere. About 25 to 30 seconds after th e initial explosion, a vapor cloud explosion
occurred. The ignition source for the vapor clou d was thought to be the gas boilers that were
immediately across the road from the reactor.
Extensive property damage occurred in the immediate area and severe damage occurred
throughout the plant. Figure 15.4, shows the ca lculated extent of the flammable vapor cloud,
extending to the boiler area.
Figure 15.3. Schematic of oxidation reactor
(Celanese)
|
4 | 1 Introduction
Describing groundbreaking CCPS work in 2005, J ones and
Kadri (Ref 1.8) adapted these published definitions to process
safety and recognized the link of culture to management:
“For process safety management purposes, we propose the
following definition for process safety culture: The combination of
group values and behaviors that determine the way process
safety is managed .” (emphasis added)
In the wake of its investigation of a refinery explosion in Texas
City, TX, USA, the US Chemical Safety Board (CSB) leveraged the
CCPS work J ones and Kadri described (Ref 1.9). CSB recommended
that the com pany conduct an independent assessm ent of process
safety culture at their five U.S. Refineries and at the Corporate
level. The resulting Baker Panel report (Ref 1.10 identified
num erous culture gaps and improvement opportunities. They
then went on to say, “We are under no illusion that deficiencies in
process safety culture, management, or corporate oversight are
limited to the company.” This statement proved to motivate many
process safety culture improvem ents in refining and chemical
com panies globally.
Additional study led CCPS to define process safety culture
based on the critical role of leadership and management. CCPS’s
Vision 20/20 (Ref 1.11) CCPS stated that a committed culture
consists of:
1. Felt leadership from senior executives. Felt leadership
m eans more than a periodic mention of process safety
in speeches and town hall meetings. It means that
executives feel a deep personal commitm ent and
remain personally involved in process safety activities.
2. Maintaining a sense of vulnerability.
3. Operational discipline, the performance of all tasks
correctly every time. |
248 INVESTIGATING PROCESS SAFETY INCIDENTS
appropriate root cause. ( N ote: In some circumstances, the facts may
not allow root causes to be identified with out further investigation.)
3. All branches and sub-branches sh ould be considered because an
individual causal factor can ha ve more than one root cause.
4. As each branch is considered, the investigator should ask if there are
other root causes associated with that category that are not listed
on the tree. The team shou ld ask, “Are there any other causes that
anyone has in mind that have not been identified?” (Predefined trees
are designed to capture most, but not necessarily all, root causes.)
5. The procedure (steps 2 through 4) is then repeated for each causal
factor, in turn.
6. When all the root causes have be en identified from the tree, the
investigator should ask why to each one in turn as a test to ensure
that they are really under lying root causes. If it is possible to identify
a lower level cause, this lower-level ca use should be recorded as the
root cause. ( N ote: This is analogous to applying the 5 Whys.)
7. Finally, the investigator should cons ider other generic causes of the
incident that are not identified by the predefined tree categories. For
example, the investigator should consider the plant operating
history. Other incidents may indicate repetitive failures that may
indicate generic management system problems.
Predefined trees are relatively easy to use and generally require less
training and effort to conduct root cause analysis than logic trees.
10.8.2 Example—Environmental Incident
The following is an example of the use of a predefined tree to analyze an
environmental incident. While the st ructure (number of branches and levels)
and terminology of predefined trees vary, this exampl e demonstrates the
basic method.
During a normal night shift at a process plant, a temporary water
treatment unit, operated by cont ract personnel, overheated and
released hot, low pH water to one of the plant’s outfalls. This |
xxxviii
Process Safety
Information (PSI) Physical, chemical, and toxicological in formation related to the chemicals,
process, and equipment. It is used to document the configuration of a
process, its characteristics, its limitations, and as data for process hazard
analyses.
Process Safety
Management
(PSM) A management system that is focused on prevention of, preparedness
for, mitigation of, response to, and restoration from catastrophic releases
of chemicals or energy from a pr ocess associated with a facility.
Process Safety
Management
Systems Comprehensive sets of policies, proc edures, and practices designed to
ensure that barriers to episodic incidents are in place, in use, and
effective.
Protective Action
Criteria (PAC) Protective Action Criteria are esse ntial components for planning and
response to uncontrolled releases of hazardous chemicals. These criteria,
combined with estimates of exposure, provide the information necessary
to evaluate chemical release events fo r the purpose of taking appropriate
protective actions.
Protective Action Criteria includes AEGL, ERPG, and TEEL and is available
in 3 levels for over 3100 chemicals.
Pool fire The combustion of material evaporating from a layer of liquid at the base
of the fire.
Reactive
chemical A substance that can pose a chemical reactivity hazard by readily
oxidizing in air without an ignition source (spontaneously combustible or
peroxide forming), initiating or prom oting combustion in other materials
(oxidizer), reacting with water, or self-reacting (polymerizing,
decomposing or rearranging). Initiation of the reaction can be
spontaneous, by energy input such as thermal or mechanical energy, or
by catalytic action increasing the reaction rate.
Recognized and
Generally
Accepted Good
Engineering
Practice
(RAGAGEP) A term originally used by OSHA, stem s from the selection and application
of appropriate engineering, operating, and maintenance knowledge
when designing, operating and maintaining chemical facilities with the
purpose of ensuring safety and pr eventing process safety incidents.
It involves the application of engineering, operating or maintenance
activities derived from engineering knowledge and industry experience
based upon the evaluation and analyses of appropriate internal and
external standards, applicable codes, technical reports, guidance, or
recommended practices or documents of a similar nature. RAGAGEP can
be derived from singular or multiple sources and will vary based upon
individual facility processes, materi als, service, and other engineering
considerations. PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION |
A.4 Report References | 225
NPO Association for the Study of Failure (ASF) of Japan Incident
Database (Continued)
(For incident reports J1–J163: see www.shippai.org/fkd/en/lisen/cat102.html)
Code Investigation
J112 Explosion in the Piping Caused Due to a Back Flow of Ammonia in
the Amination of 5-Chloro-1,2,3-Thiadiazole (1980)
J113 Fire Caused By Explosion of P-Nitrophenol Sodium Salt Due to
Friction During Transfer With a Conveyor (1979)
J114 Explosion and Fire Caused By a Runaway Reaction On Start-Up of
the Preparation of an Adhesive Manufacturing Plant (1978)
J115 Explosion of DMTP Due to Improper Temperature Control at a
Manufacturing Plant of Pesticide Intermediates (1977)
J116 Leakage of Toxic Substances at a Chemical Plant (1976)
J117 Explosion Due to Heat of Adsorption of an Adsorption Tower Used
to Deodorize a Methyl Acrylate Tank (1976)
J118 Explosion at a Reactor Caused By a Temperature Rise in a Recovery
Process for Hydroxylamine Sulfate at a Pharmaceutical Production
Plant (1974)
J119 Disaster of Chemical Plant at Flixborough (1974)
J120 Spouting of High-Temperature Liquid from the Reactor Due to a
Hot Spot Formed On Stopping the Agitator (1974)
J121 Rupture of a Vacuum Distillation Drum for 4-Chloro-2-Methylaniline
Caused By Air Leakage and Misjudgment (1973)
J122 Leakage and Explosion of a Vinyl Chloride Monomer Due to Valve
Damage at Distillation Column Feed Piping at a Plant
Manufacturing Vinyl Chloride Monomers (1973)
J123 Fire Caused By Stopping an Agitator in a Liquid Seal-Type Reactor
During a Temporary Shutdown Procedure at an Ethylidene
Norbornene Plant (1973)
J124 Explosion of 2-Chloropyridine-N-Oxide Left As a Distillation Residue
(1973)
J125 Explosion Due to Delayed Start of Agitation at the Start-Up of
Reaction of O-Nitrochlorobenzene (1973)
J126 Runaway Reaction During Manufacturing Pesticide Due to a
Decomposition Reaction of Tarry Waste (1973)
J127 Explosion Due to Condensation from Miss-Charge of Toluidine Into
a Vessel of Diketene (1972)
|
3.4 Consequences of Not Learning from Incidents | 35
institute systems to transfer the experts’ knowledge into the corporate
memory.
Assessing Blame Rather than Correcting Root Causes
Across industries, we continue to struggle to perform in-depth incident
investigations that identify root causes that can be corrected. Investigators
often stop once they identify the individual who made the ultimate error and
correct the error by punishing the individual.
Although punishment could potentially prevent the individual from
making the same error, this step doesn’t address systematic process or design
problems or work conditions that led to the error. That makes the error likely
to happen again. Worse, it may drive others in the organization to hide
incidents and near-misses, preventing the company from being able to fix the
root cause.
The desire to avoid blame may also lead managers to limit the scope of
an incident investigation or improvement recommendations. This action may
be driven by legal counsel seeking to avoid fines or lawsuits or by other
personnel fearing a negative performance review.
Misplaced Conservatism
One of the ironies of the human condition is that as much as we seek to
continuously improve, innovate, and advance technology, we also resist
change, even when change is well justified. Both extremes—progressivism and
conservatism—can create problems in process safety. In plants and
companies with a culture of doing business as usual, opportunities to improve
from learning may be unnecessarily blocked.
Most of the factors described in this section can lead to gradual
degradation of culture and corporate memory. This outcome can only be
combatted by seeking continuous improvement. This will help ensure that any
institutional knowledge that may have briefly been forgotten will become
reinstated within the culture.
3.4 Consequences of Not Learning from Incidents
When we don’t learn from incidents, we run a higher risk of repeating them.
Learning from incidents is important because human lives are at stake.
Incidents can result in fatalities and/or injuries to employees or to the public.
They can result in property damage to the plant and the surrounding area. |
OVERVIEW OF RISK BASED PROCESS SAFETY 39
3.2.1 Pillar: Commit to Process Safety
The aim for the first pillar is to ensure that the foundation for process safety is in
place and embedded through out the organization.
RBPS Element 1: Process Safety Culture
This element describes a positive environment where employees at all levels are
committed to process safety. It starts at th e highest levels of the organization and is
shared by all. Process safety leaders nurtur e this process. Process safety culture is
differentiated from occupational safety culture as it addresses less frequent major
incident prevention cultures as well as occupational safety.
This element highlights the necessary role of leadership engagement to drive
the process. Safety culture should not be thought of as a passive outcome of a
specific work environment; rather it is something that is managed and improved.
Example Incident: Deepwater Horizon
The Deepwater Horizon National Commission identified poor process safety
culture as a leading cause of that incident, while simultaneously having a positive
occupational safety culture and achievement of excellent performance with
traditional safety indicators. High drilling co sts, delays, and a desire to move onto
the next task led to poor decision making and discounting of danger signs. Similar
issues have been apparent in the downstream industry as well. The US National
Academies (2016) reviewed how to strengthen safety culture in the offshore oil
and gas industry and they endorsed the BSEE nine characteristics of a positive
safety culture. The UK HSE has also addresse d this topic in multiple publications,
including Reducing Error and Influencing Behaviour (HSE, 1999).
RBPS Application
Process Safety Culture provides an overview and suggested means on how to
improve process safety culture.
RBPS Element 2: Compliance with Standards
Organizations should comply with applicable regulations, standards, codes, and
other requirements issued by regulators and consensus standards organizations.
These requirements may need interpretation and implementation guidance. The
element also includes proactive development activities for corporate, consensus, and
governmental standards.
RBPS Element 3: Process Safety Competency
This element addresses skills and resources that a company should have in the right
places to manage its process safety hazards . It includes verification that the company
collectively has these skills and resources and that this information is applied in
succession planning and management of organizational change. |
32
The layers of protection can be expensive to build and maintain
throughout the life of the process . Initial capital expense, and the
costs of operation, training, and maintenance, along with
diversion of scarce and valuable technical resources into maintenance and operation of the ac tive layers of protection can
add significantly to plant operatin g budgets. In particular, SISs
are difficult and expensive to design, procure, and maintain. Also, to maintain the calculated le vel of reliability of SISs, i.e., the
safety integrity level (SIL), interval testing schedules and procedures must be diligently followed.
For these reasons, it is more advantageous to design or modify the
process to be able to inherently withstand the hazard(s) if possible,
rather than, as the old adage says, add more “bel ts and suspenders.” For
example, it is inherently safer to design the maximum allowable working
pressure in a process to be higher than the maximum pressure that can
be achieved in the process rather than to add additional active
overpressure protection devices s uch as relief valves (although relief
valves may be required by applicab le regulations and/or engineering
codes and standards). Figure 2.4 shows the relationship between
inherently safer designs and layers of protection. This figure depicts the
concept of layers of protection (inc luding the inherently safer solutions
in the “design” layer) representing how the layers of an onion build upon
each other to form the whole (adapted from Ref 2.29 CCPS Metrics)
2.8 INTEGRATING INHERENT SAFETY IN PROCESS RISK
MANAGEMENT SYSTEMS
How does inherent safety fit into an overall process risk management
program? As discussed above, “risk” is defined as “the likelihood that a
defined consequence will occur.” Efforts to reduce the risk arising from the operation of a chemical processing facility can be directed toward reducing the likelihood of incidents (incident frequency), reducing the
magnitude of the loss, injury or damage should an incident occur
(incident consequences), or eliminating the potential consequences altogether.
A key engineering risk tool is a management system appropriate for
the risks being addressed (i.e., heal th, occupational safety, process |
100 | 3 Leadership for Process Safety Culture Within the Organizational Structure
Succession Planning
Succession planning is an important way to maintain process
safety culture and PSMS performance through leadership
changes. A good succession plan, supported by a sound
organizational m anagem ent of change process, helps maintain
com petency, performance, and culture during organizational
changes.
A succession plan ensures that qualified and motivated
employees are ready to take over when a key person leaves the
organization. Whether or not the actual successors are known, a
succession plan includes experience and competency
requirements for potential replacements. Having a succession
plan demonstrates to stakeholders that the organization is
com mitted m aintaining consistent functioning at all times,
including during times of transition. The HR Council (Ref 3.24)
offered an example highlighting what can happen without
succession planning:
A mid-sized organization relied heavily on the corporate memory,
skills and experience of a longtime employee. In her final position,
she was responsible for office administration including payroll
and budget monitoring. During her career, she held many
positions and understood well the organization's operations and
history. Her unexpected death was both an emotional blow and a
wake-up call to her colleagues. Everything she had known about
her job was “in her head.” While management discussed regularly
the need to document her knowledge to pass it on to others, this
had never happened. Ultimately, the organization did regroup
and survive the transition, but employees experienced high stress
as they struggled to determine what needed to happen when. A
great deal of time and effort was spent recreating systems and
processes and even then, some things fell through the cracks
resulting in the need to rebuild relationships with supporters. |
15.4 PROCESS ROUTE SELECTION – EARLY R&D EXAMPLE
Inherent safety has been institut ionalized into procedures that
researchers must follow when develo ping a process chemistry and/or a
process design. Researchers are required to review hazards and
document a process hazards analysis (PHA) for each experimental set-
up and/or significant change in that set-up. A checklist is a required part
of that PHA effort and inherent safety (IS) questions ar e included in the
instructions for completing the checklist.
The format (template) for technica l reports on product, chemistry,
and process development includes a section on IS, as does the report format for applying for permission to seek a patent. The principal instruction on the template for ea ch is similar to the following:
“If the process or chemistry being addressed is aimed at the implementation of a new manufacturing process, or improvements/changes to an existing manufacturing process, then a
discussion of the anticipated hazard/risk level at the commercial scale
must be included. This discussion should be from an IS perspective and
include consideration of the quantity of hazardous materials involved, and the severity of process conditions. The use of a standard “index” sheet—a form that dictates IS be considered—is required.”
The index sheet (Ref 15.9 Heikkila) is a chart that gives five levels of
definition (from low to high) for toxicity, flammability, and reactivity (i.e., the material factor), for quantity (i .e., the quantity factor), and for
reaction severity, pressure, tempera ture, potential for corrosion or
erosion, dust content, operability, and experience (i.e., the process f a c t o r ) . T h e r e s e a r c h e r i s a s k e d t o a s s i g n a “ l e v e l o f s e v e r i t y ” t o e a c h factor, and to sum them.
The higher the resulting number, the more hazardous the chemistry
or process is, from an IS standpoin t. Several alternative chemistries
and/or processes must be proposed , and the “index” sheet used for
them as well. If competing chemistr ies and/or processes exhibit a lower
total “level of severity,” the research er is obligated to defend his choice.
No chemistry that exhibits "severe" factors in all categories is accepted. 411 |
232 | 6 Where do you Start?
com pletely in one effort. Try to make improvem ents in each core
principle one or two at a time. When selecting core principles to
address, it may be helpful to address those at the beginning of the
list first.
The Nature of Management System s and Documentation
Models
Section 4.4 discussed the institutionalization of PSM S via
centralized and decentralized organizational models. B oth have
advantages and disadvantages. If the nature of the PSM S is found
to contribute to process safety culture issues, decide whether the
m odel needs to be more centralized or more decentralized.
The m any types of documentation required by the PSMS serve
a critical role in assuring PSM S performance. However, when
documentation requirements are redundant, use software that is
not user-friendly, or appears to not have a purpose, the stage is
set for a check-the-box mentality and the normalization of
deviance . Often, carefully designed docum entation systems can
m ake documentation easier. Involving the users of the
documentation in the design process can also help in building the
culture.
Com munication Communication break-downs between silos rank high am ong
the many comm unication barriers discussed in section 2.4.
Considering the multi-functional nature of PSMSs, connecting
silos is essential to help inform ation flow more freely between
groups and individuals. This also helps reinforce the key point that
the process safety culture and PSMS requires full participation
and integration.
B reaking down silos can be accelerated by getting workers in
one group to be interested in and fam iliar with the PSMS elements
their co-workers in another group have responsibility for. This can
lead to m utual appreciation about each other’s roles and |
120 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
Figure 7.1. Damage to Concept Sciences Hanover facility
Courtesy Tom Volk, The Morning Call
(CSB 2002)
CSI developed a four step process to make 50% HA:
1. Reaction of HA sulfate and potassium hydroxide to produce a 30 wt.% HA and
potassium sulfate aqueous slurry:
2. Filtration of the slurry to remove precipitated potassium sulfate solids.
3. Vacuum distillation of HA from the 30 wt . % solution to separate it from the
dissolved potassium sulfate and produce a 50 wt. % HA distillate.
4. Purification of the distillate through ion exchange cylinders.
The distillation process is shown in Figure 7.2. The charge tank was a 2,500 gallon (9.5 m3)
tank. In the first step of the distillation, a pump circulated 30 wt. % HA to the heating column,
which is a vertical shell and tube heat exchanger.
The HA was heated under vacuum by 49 °C (120 °F) water. Vapor was drawn off to the
condenser and collected in the forerun tank and concentrated HA was returned to the charge
tank. When the concentration in the forerun tank reached 10 wt. %, it was then collected in the
final product tank. At the end of the first step of the distillation, the HA in the charge tank was
at 80 - 90 wt. % HA. At that point, the charge tank was supposed to be rinsed with 30 wt. % HA.
The first distillation done by CSI began on Monday afternoon, February 15, 1999. By
Tuesday evening, the HA in the charge tank wa s approximately 48 wt. %. At that time, the
process was shut down for maintenance after it was discovered that water had leaked into the
charge tank through broken tubes in the heater column. The distillation restarted on Thursday
|
200
Carriers and shippers have worked together to improve
transportation safety. The American Association of Railroads has agreed
to designate routes that handle 10,000 loads per year or more of chemicals as “Key Routes.” Key Routes receive upgraded track, enhanced
equipment to detect flaws in equi pment or trackage, and lower speed
limits.
“Just-in-time” supply of materi als may affect the mode of
transportation and could actually incr ease associated risks. For example,
if drums of a chemical are stockpile d near a user, the material is not
under the same level of control that could be provided by either the
supplier or user if the inventory was maintained in a storage tank at one
or the other facility. This type of risk should be included when
contemplating “just-in-time” shipments.
8.10.4 Improved Transportation Containers
Transportation risk can be reduced by applying inherently safer design
principles to transportation cont ainers. Some examples of design
improvements are as follows:
The shipment of environmentally-sensitive materials in general
purpose rail cars has been phas ed out, and DOT specification
105 pressure cars are used instead (Substitution ).
Thermal insulation can be used to maintain lower temperatures
in the containers and to provide improved protection from fire
(Moderation ).
Baffles and subdivided internal barriers reduce the amount of chemical that can be released if only one compartment is breached ( Minimization ).
Non-brittle containers can be us ed to improve resistance to
impact or shock damage.
In addition, transportation cont ainers can and have been made
more inherently robust and enhanced l ay er s o f p r ote cti on h a ve b e en added to them as follows:
Rail car design, particularly for certain cargoes, has been enhanced so that they can with stand more serious and energetic
crashes and derailments without breaching. For example, the |
118 Human Factors Handbook
Competency includes not only the applic ation of technical skills and knowledge,
but non-technical skills such as communica tion; this is important for supervisory
roles.
10.3 Competency Management
Competency Management refers to methods used to categorize and track the
development of employee’s competency. Th is allows the organization to track
progress and identify training needs.
Clear competency performance standards should be developed. People should
also receive appropriate training and devel opment opportunities, to maintain their
competency over time. Key steps in ac hieving process safety competency are
shown in Figure 10-1. The five phases follow:
• Phase 1: Establish Requiremen ts – Determine competency
Before starting Competency Managemen t, it is important to identify
activities that may affect operational, and/or occupational safety. Risk
assessments are especially useful here, as they can identify safety critical
tasks (see Chapter 6 for advice on Safety Critical Task Analysis).
All the requirements for the position should be identified. As a priority,
the focus should be on safety critical task and required competency,
followed by all other tasks’ competency requirements.
The next step is to identify and define operational competency and
performance standards for these tasks.
• Phase 2: Identify Learning Requirements
This phase includes assessment of the gap between individual and team
competency, and the competency that individuals need to develop. It is
then necessary to identify the learning required to bridge the gaps,
including the type of learning most suitable to develop and demonstrate
the competency. This includes providing a description of learning
objectives, to aid development of the on-the-job learning and training
programs in Phase 3.
• Phase 3: Develop Competency
Relevant learning and coaching programs are designed to target
competency gaps and fulfil the learning objectives defined in Phase 2.
These programs are provided to selected individuals.
|
Piping and Instrumentation Diagram Development
198
(wet gas) is higher than for liquids with non‐tolerable
gas content.
●As the gas movers are large, their moving elements may have huge momentum and in the cases of a quick trip in the system, they may move for a while even after shutdown. Therefore there should be some systems to take care of gas movers in those situations. Some of the required actions could be implemented as part of the interlock system. Interlock systems will be discussed in Chapter 16.
●If the to‐be‐pressurized gas is flammable, more cau-tion should be taken in design. This is mainly because by pressurizing a gas, it will be hot.
●Compressors may be placed in an enclosed or semi‐enclosed building for different reasons. One reason could be the sound level around the com-pressor. The other reason is to provide a dedicated space for compressors for ease of inspection by operators. The “compressor building” could be a multi‐story structure for the ease of inspection and maintenance.
10.8.3
Gas M
over Drives
The same drives of centrifugal pumps are available for gas movers too. Electric motors, turbines (steam driven and gas turbines), and internal combustion motors are some of them.10.8.4
Auxiliar
y Systems Around Fluid Movers
Auxiliary systems around fluid movers could be support -
ing systems for different components of the fluid mover. A fluid mover consists of drive section and fluid mover section. A “connection” attaches these components together (Figure 10.40).
The “connection” could be shaft, gear box, crankshaft
or a combination.
Each of the above components may need some type of
auxiliary system. Some of these auxiliary systems are listed in Table 10.12.
The seal type for the gas movers could be the same
type of seal types for liquid movers. The liquid mover seal type was discussed before and is a “wet type sealing. ” For a long time it was assumed that the only type of seal for compressors are the wet type. But later it was recog-nized that even a gas could be used as a sealing fluid. Then a newer type of sealing system, the dry gas seal, came on the scene.
In a dry gas sealing system an inert gas like nitrogen
gas can be used as the sealing gas.
Drive Connection Fluid mo ver
Figure 10.40 Fluid mo ver and drive as a pair.
Table 10.12 Fluid mo
ver auxiliary systems.
Components Type Required auxiliary system
Drive Electric motor ●Bearings may need cooling
●The majority of motor blocks are generally air cooled and no specific system is required.
However some of them need forced air cooling and air should be cooled (by air or water) and recirculated. Some huge electric motors could be oil cooled, then a cooling system is needed
Internal combustion engine (diesel, gas)
●Pistons need lubrication
●The motor block needs cooling
Air operated drive ●No specific auxiliary system is required. Only plant air should be piped
Solenoid operated drive ●No specific auxiliary system is required. Only DC electricity is required
Steam turbine ●The block may need cooling
Gas turbine ●The block needs cooling
Connection Shaft ●The penetration point should be sealed, lubricated, cooled, and flushed
Gear ●Gear box may need lubrication
Crankshaft ●Crankshaft may need lubrication
Fluid moverLiquid mover
●Bearings may need cooling
●(As mentioned) penetration points should be sealed, cooled, and flushed
●In compressors the block should be kept cooled but this is done by the intercooler shown on the main process P&ID and not the auxiliary P&IDGas mover |
98 | 7 Keeping Learning Fresh
You could also create your own learning exercise keyed to this style of
communication using readily available short videos, for example the CSB video
about the Illiopolis, IL, USA incident. Show the video (CSB 2007) and then ask
participants to break out into groups to answer these questions:
• Why did the operator use the emergency air hose without thinking?
• Why did the supervisor run upstairs to stop the release rather than
evacuating?
• For extra credit: Why was a hose clearly labeled “Emergency Air” provided
under each reactor?
• Based on your answers to these questions, how would you ensure your
team acted properly?
During the report-back time, steer the conversation toward the underlying
issues, including normalization of deviance, conduct of operations, human
factors, and where in the PHA this scenario might have been captured.
Here’s another way to communicate in a logical-mathematical style about
the proper response to person-down incidents. Create a bulletin, poster,
video, or presentation showing that the incidence of health conditions like
heart disease and diabetes is lower among workers in the process industries
than in other industries. If possible, compare your company’s own statistics
for these conditions to the rate in the general population. Then ask, “In a
facility like ours that handles toxic materials and asphyxiant gases, why would
the person have collapsed on the floor? What should you do?”
7.5 Kinesthetic Intelligence
People with kinesthetic intelligence learn best when they can have hands-on
learning experiences. To support this kind of learning, aspects of some
incidents can be simulated under safe conditions: for example, controlled
demonstrations of chemical reactivity, vapor cloud, and dust explosions.
Simulations are especially effective when observers can feel some heat from
the fire or feel and hear the pressure wave from the explosion. Computer
simulations can also be effective learning tools, although it is harder to
simulate the heat or pressure wave. Role-playing is another a beneficial way
to learn, especially if a moderator can supply stimuli and sound effects that
help the participants imagine what an explosion or fire feels like.
Another aspect of kinesthetic learning is learning while moving. After a
major incident occurred in its facility, one company set up a walking path with |
EDUCATION FOR MANAGING ABNORMAL SITUATIONS 103
This type of arrangement works we ll for HAZOP studies and has the
added benefit of providing feedback to designers and engineers who are
not on the front-line and may not have a full appreciation of potential issues
with the equipment they are providing. A common criticism offered by
operating personnel is that the designers do not have to run the process
and therefore sometimes fail to have an appreciation of some of the
problems that certain desi gn features can create.
Traditional training and learning processes are normally targeted at
teaching personnel to operate the process per standard operating
procedures (SOPs), step-by-step tasks or checklists, and using the
computerized process control system. Th e training tools that are used are
typically very structured to ensure consistency in how the training
information is communicated and how und erstanding is verified. Although
these types of tools have been demonstrated to work well, they may not be
the optimum tools for educating for abnormal situations. These matters are
discussed further in Chapter 5.
No matter the training objective, logistics of the training session
including time, setting, frequency, and number of personnel on shift, as well
as type of training, (e.g., Classr oom / Computer/ Desktop / One-on-One)
should be considered in advance. Management of the training should
include a system for enforcement of the training and metrics to measure
the effectiveness of the program, as discussed in 6.2. The next section
describes some of the traini ng topics and structure.
4.3.2 Structure of Training Topics
4.3.2.1 Basic Process Operations
For front line control room operators and field operators, an introductory
understanding of the process chemistr y, potential chemical interactions,
relationships between temperature, pressure, flow, and level as they relate
to process operations are essential to building an operator’s knowledge and
the ability to recognize and respond to abnormal situations. Training in
these basic relationships can be accomplished using basic process
simulation software that typically runs on a desktop personal computer.
Additionally, the training may be accomplished in informal training sessions
with senior plant personnel or in formal training with chemical process
instructors. |
208 INVESTIGATING PROCESS SAFETY INCIDENTS
concerns had grown to the point that further launches were
postponed until an attempt was made to remedy the
situation. But these remedies were in effective and did not
deal with the causal factors or root causes of the problem
joint. Despite all that was known about the O-ring problem,
a decision was made to launch the Cha llenger on a cold
January morning with deva stating consequences. The
Challenger space shuttle disaster is an excellent example of
the principle that apparently simple mechanical problems
are related to more complex underlying causes rooted in
management systems. The recommendations submitted by
the presidential commission focused on root causes. These
involved changes in management systems that would not
only fix the ring joint problem, but also the systems,
procedures, and overall appr oaches to identifying,
evaluating, resolving, monitoring, and auditing safety-related concerns.
10.3 M ETHODOLOGIES FOR ROOT CAUSE ANALYSIS
10.3.1 5 W hys Technique
The 5 Whys is a simple methodology for identifying root caus es that involves
repeatedly asking the question “why ?”. The methodology is easy to
understand and perform, and the technique adds so me structure to group
brainstorming. Large quantities of in formation and data are not necessary
(although useful for complex process safety incidents), and therefore the
technique is suitable for minor incidents, especially those involving human
factors and interactions. The 5 Whys is also widely used as an integral part
of Kaizen, Lean Manufacturing, and the Six Sigma methodology [e.g., the
Analyze phase of Six Sigma DMAIC (Def ine, Measure, Analyze, Improve,
Control) ].
Although called 5 Whys, five is only a rule of thumb, and sometimes the
investigation team will ask “why?” more or fewer than five times. The technique requires that th e investigation team asks “why?” a negative event
occurred or undesirable condition existed (i.e., causal factors), and then asks
“why?” enough times to reach a management system deficiency. The process
is repeated until all the causal factors ha ve been considered. In essence, this
is analogous to a logic tree approach wi thout actually draw ing the logic tree. |
100 PROCESS SAFETY IN UPSTREAM OIL & GAS
Smaller onshore oil facilities tend to fo llow API and related standards (listed
above), and either RBPS or the OSHA PSM regulation (although they may be
exempt formally) for structuring thei r process safety management system.
Regulations
An overview of regulations was provided in Section 2.8. Specific to onshore
production, OSHA and EPA share responsib ility in the US for onshore regulations
for facilities exceeding nominated invent ory thresholds. Similarly, PHMSA
regulates pipelines. OSHA PSM has a focus on worker safety, while EPA RMP
(Risk Management Program) has a focus on offsite / public safety and environmental
incidents.
OSHA does not require a single document collecting all elements of the PSM
program, just that all elements must be present. Conversely, the EPA does require a
risk management program document.
For facilities in Europe and parts of Austra lia (e.g., Victoria), a safety case must
be prepared. The EU regulation is known as the Seveso Directive, originally passed
in 1986, and updated twice to address serious incidents that were not well covered.
This regulation was covered in Section 2.8.
For larger onshore production facilities that exceed regulated thresholds, both
the EPA RMP and the safety case (now known as safety report) requirements in the
EU Seveso III Directive require that important parts of the major hazard plan be
documented. This includes a listing of hazardous materials, the facility description,
hazard identification and risk ranking, th e management system, and the emergency
response plan. In the US, most states ha ve regulations for production facilities.
Both RMP and Safety Reports must address emergency response and this topic
is outlined in Section 5.3.4.
Company Practices
Most companies have documented practices and procedures that describe how the
company applies regulations, standards, and lessons learned. Additionally, large
companies have their own internal guidelin es for engineering and process safety.
5.3.2 Hazard identification and Risk Analysis
The Hazard Identification and Risk Analysis approaches described in Chapter 4 also
apply to onshore production. Refer to Chapter 4 for further details. The main
methods used include What-If, the What-If Checklist, and HAZOP (Hazard and
Operability Study).
What-If
What-If examines operations for possible deviations to see what the consequences
might be and what safeguards are employed. The safeguards listed may be barriers,
barrier elements or degradation controls as discussed in the bow tie methodology
(CCPS, 2018c). What-If or the What-If Chec klist can be employed early in a process |
54 Guidelines for Revalidating a Process Hazard Analysis
• Are causes meaningful? A cause such as “opera tor error” for a “High
level” deviation is not meaningful to anyone outside of the PHA
team, and its specific meaning will probably be forgotten by the
PHA team members themselves a few days after the PHA meetings
are complete. A more meaningful statement of the cause might
read, “operator fails to remain with the tank during the fill step and
stop the flow at the ‘full’ mark,” or “operator fails to stop the flow at
the ‘full’ mark due to being distracted by another process alarm.” It
is easier to understand and revalidate causes that are more
specific.
• Do the stated consequences pr esume failure of all safeguards?
Taking credit for safeguards in the consequence definition is a
common PHA flaw. If this error is pe rsistent throughout the PHA, it
is a sign the PHA team did not accurately document and discuss
worst credible consequences in th e PHA. Consider the possibility of
high pressure in a vessel. If “process shutdown” was listed as the
consequence, the prior PHA team may have assumed the high-
pressure interlock would shut th e process down as designed and
disregarded the potential for cata strophic vessel overpressure. If
“discharge to the flare” was liste d as the consequences, the prior
PHA team likely assumed the pres sure relief valve worked as
intended to protect the vessel. PHA teams may be willing to accept
the risk of a particular outcome based on some (but not all) of the
safeguards working, but if a qualitatively worse outcome went
unrecognized, risk may not be managed as intended. In the case of
vessel overpressure, the unacknowledged consequences are that
the vessel might rupture (if the maximum allowable working
pressure [MAWP] exceedance is great enough), and the prior PHA
team did not document its implicit acceptance of that risk.
• If a consequence of interest might result from successful
operation of a safeguard, is it addressed as well? The March 2005
explosion at a Texas City refinery [34] did not involve failure of all
safeguards. As the pressure in a distillation column rose, the
pressure safety valves functioned as intended, discharging
flammable liquid above its normal boiling point to the atmospheric
blowdown stack and releasing a large flammable vapor cloud.
Ignition of the cloud led to an explosion that killed 15 and injured
180 at the refinery. Similarly, the fire protection systems worked as
designed to suppress a 1986 agrichemical warehouse fire in
Switzerland. The firewater runoff carried highly hazardous
chemicals into the nearby Rhine River and poisoned aquatic life
downstream to the North Sea [35]. Thus, it is important that the
prior PHA team also considered scenarios, particularly those |
PROCESS SAFETY AND MANAGEMENT OF ABNORMAL SITUATIONS 19
Example Incident 2.2 – Bayer Crop Science Plant, ( cont. )
Lessons Learned in relation to abnormal situations:
1) For management / engineers:
Overly complex operating procedures
Inadequate operator training on the newly installed DCS
Temporary changes not evaluated
Malfunctioning or missing equipment (faulty new relay caused
both centrifuges to trip, solven t drip line was missing a valve)
Insufficient technical expertise available in the control room
during the restart
Operational readiness review was inadequate
2) For supervisors / operators / technicians:
Deviation from written operating procedure (several required
steps were not completed)
Safety-critical equipment bypassed (interlocks on residue
treater) or not operable (toxic gas monitoring system not in
service)
Misaligned valves
Example Incident 2.1 an d Example Incident 2.2 – (Broadribb, CSB)
involved transient operations of startup and shutdown. However,
abnormal situations can also occur during normal operation, as Example
Incident 2.3 (HSE 1997) illustrates . More details of Example Incident 2.3
are also provided in Chapter 7.2.
|
Piping and Instrumentation Diagram Development
230
12.15 Deciding on an Emergency
Release C
ollecting Network
One important issue regarding P/VRDs is the final destina-
tion of the released fluid. An emergency release collecting network could be used to collect the instantaneous releases from PSDs and direct them toward the disposal system.
Figure 12.24 shows a simple schematic of an
emergenc
y
release collection network.
The emergency network has several requirements,
which are shown in Figure 12.25.
As is visible from Figure 12.25, the main header should
be sloped toward the disposal system. If there is needed PGor “pressure switch to
control room
Burst sensor
PAH
SET @ 146 PSIg(d)(c)(b)(a)
123
Figure 12.19 Combina tion of safety valves and rupture disks.
Figure 12.20 Combina tion of safety valves and rupture disks.PG
Figure 12.21 A combined solution t o deal with leakage of the
rupture disk upstream of the PSV.
Utility water
Flush ring
Figure 12.22 A PSV with a flush ring .
Figure 12.23 Rupture disk upstr eam and downstream of a PSV on
the outlet of a PD pump. |
7.2 Sustainability of Process Safety Culture |241
The last point may seem circular, but reflects a key tenet of
sustainability. Sustainability must be intentional. That is why
“Learn and advance the culture ” is one of the core principles of
process safety culture. More generally, each of the core principles
is required for a strong process safety culture to endure.
7.2 SUSTAIN ABILITY OF PROCESS SAFETY CULTURE
Process safety culture, like any culture can degrade quickly
without comm itted effort to sustain it. Almost any event, good or
bad, can create conditions that unravel previous efforts. The
following exam ples describe events that can degrade culture, how
this could happen, and what leaders can do to sustain the culture.
Serious process safety incidents Process safety incidents with severe consequences can
represent a crossroads event in the life of an organization. In a
strong or improving culture, leaders take the opportunity to re-
exam ine the process safety culture and PSMS, learn and apply the
lessons-learned broadly across the company, and re-commit to
process safety.
However, in a weaker or degrading culture, managem ent m ay
turn the investigation to finger-pointing and a search for a
scapegoat. In response to regulatory and public pressure, the
com pany may seek a legal settlement. While this is a norm al
practice, a weaker culture will treat the settlem ent as evidence
that the causes of the incident have been resolved. Such a
settlement would not deter a stronger culture from seeking
improvement.
Incidents can som etimes be caused or contributed to by an
individual who takes actions that are forbidden by company policy
(e.g., violating lock-out/tag-out). The investigation team should
determ ine if it was only the one person breaking the rules, or part
of a pattern where policy violations are common. If the policy
violation was an unusual event, the com pany should not be |
9.2 Seek Learnings | 123
first start-up following the replacement of spent catalysts with an
improved catalyst that the plant had not previously used.
Before introducing MPK, the catalyst bed was heated by circulating
ethylbenzene through the reactor and an external heat exchanger. The
company did not know that the new catalyst could react with
ethylbenzene at temperatures that could typically be reached during
start-up due to normal temperature fluctuations.
Due to the reactor fluctuations, the liquid level in the vapor-liquid
separation tank on the flare line also fluctuated widely. Every time the tank
reached high level, an interlock would close the valve between the tank
and the flare and had to be manually re-opened by an operator when the
liquid level dropped. Just before the runaway, an operator had neglected
to re-open the valve to the flare.
A thermal runaway occurred. With the valve to the flare left closed, the
resulting pressure could not be relieved, leading to the explosion.
Although Jason was not able to find other public cases of runaway
reactions involving catalyst pellets, he did find several other cases where
unexpected runaway reactions occurred:
Oita, Japan, 1996
During a trial batch of a new pesticide, an
intermediate was held at high temperature during
a process delay due to a pump failure. The intermediate self-reacted
exothermically, leading to an explosion that injured an operator and
damaged the production building.
Kitakyushu, Japan, 1996
A contaminant present when raw material was fed
to a resin intermediate process led to an explosive
decomposition of the raw material. The contaminant back flowed from
the vapor treatment system. While no one was injured, the plant was
destroyed and did not restart. The contaminant had entered the vapor
treatment system from another part of the process.
See Appendix
index entry J30
See Appendix
index entry J35 |
256 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
Table 12.5 continued
Process Phase Example Objectives Hazard Analysis Technique
Pilot plant Identify ways for hazardous materials
to be released to the environment.
Identify ways to deactivate the catalyst.
Identify potentially hazardous operator
interfaces.
Identify ways to minimize hazardous
wastes. Checklist
Preliminary Hazard Identification
(HAZID) Analysis
What-If
What-If / Checklist
Hazard and Operability Study
Failure Modes and Effects Analysis
Fault Tree Analysis
Event Tree Analysis
Detailed
engineering Identify ways for a flammable mixture
to form inside process equipment.
Identify how a loss of containment
might occur.
Identify which process control
malfunctions will cause runaway
reactions.
Identify ways to reduce hazardous
material inventories.
Evaluate whether designed safeguards
are adequate to control process risks to
tolerable, required or as low as
reasonably practical (ALARP) level.
Identify safety-criti cal equipment that
must be regularly tested, inspected, or
maintained. What-If
What-If / Checklist
Hazard and Operability Study
Failure Modes and Effects Analysis
Fault Tree Analysis
Event Tree Analysis
Construction and
start-up Identify error-likely situations in the
start-up and oper ating procedures.
Verify that all issues from previous
hazard evaluations were resolved
satisfactorily and that no new issues
were introduced.
Identify hazards that adjacent units
may create for construction and
maintenance workers.
Identify hazards associated with vessel
cleaning procedures.
Identify any discrepancies between as-
built equipment and the design
drawings. Checklist
What-If
What-If / Checklist
Critical Task Analysis
|
PROJECT DESIGN BASICS 173
Figure 10.9 Inherently safer design principles
(CCPS 2019 b)
The “simplify” principle addresses human fact ors which will be discussed in Chapter 16.
Humans make mistakes, even with the best kn owledge and skills. Incorporating aspects in an
engineering design to enable successful human performance will support good process safety
performance.
These four techniques make ISD sound simple, bu t in reality, it is a bit more complex. “A
technology can only be described as inherently saf er when compared to a different
technology…A technology may be inherently safe r than another with respect to some hazards
but inherently less safe with respect to othe rs…” (DHS 2010) For example, minimizing the
quantity of a hazardous material stored at a fa cility may reduce the fac ility risk; however, it
may necessitate increased transp ortation of that hazardous ma terial to supply the facility
resulting in an increased risk along the transportation route.
ISD is applicable through the life cycle stages and includes manufacturing, transportation,
storage, processing, and decommissioning. The greatest opportunity to implement ISD is
during the design phases where the implementa tion of an ISD approach only involves a
changing ink on an engineering drawing as opposed to modifying steel in a facility.
ISD is iterative during engineering design de velopment. During conc eptual phases, major
decisions are made such as use of an inhere ntly safer technology or choosing to export
product by ship versus truck. As the design details are progressed, the size of vessels is
determined, and the control systems are develo ped. In an operating facility, operating
procedures can be provided in a clear and concis e way with visual cues that makes them easy
to understand and use.
Hierarchy of Controls
Hierarchy of controls is similar, in concept, to ISD and is used in many industries. It depicts
hazard controls in order of decreasing effect iveness as shown in Figure 10.10. The first two
levels in the figure are ISD principles and ar e typically more easily implemented during the
early stages of a project prior to the detailed equipment design. The remaining levels reflect
that “It is unlikely that any technology will be ‘i nherently safer’ with respect to all hazards, and
other approaches will be required to manage the full range of hazards and risks.” (DHS 2010)
When the engineering design is finalized or the project is completed, administrative controls
are easier to implement. |
164 Guidelines for Revalidating a Process Hazard Analysis
scenarios for initial and refresher training activities. Companies often keep
current electronic copies of their PHAs on their intranet to make this information
conveniently accessible to all employees . When the PHA revalidation report is
issued, an electronic link can be easily sent to everyone who works in that
process area, those who might be affected by its hazards, and anyone else who
needs to know the revised PHA is available.
For the benefit of the next revalidation team, the PHA files could include a
record, such as an end-of-PHA checklist, identifying what information was used,
how it was used, and where it is stored (if not with the PHA itself). If a third-party
facilitator was used, a copy of their digita l files should also be retained in the
PHA files.
Finally, it is important that this valu able information be protected. Company
policies or procedures often establish retention, redundancy, and diversity
requirements for the PHA-related record s. Regulations may impose additional
requirements on some facilities. For ex ample, in the United States, companies
with processes covered by the OSHA PSM or EPA RMP regulations must keep the
initial PHA and all subsequent PHA revalidation reports, as well as
documentation of the resolution of re commendations from these reports, for
the life of the process. Covered facilities should ensure that archival copies of all
versions of the PHA documentation are maintained, regardless of the
documentation option used for prior PHA reports.
The “life of the process” may span de cades, so the archive copies should
resist both physical loss (e.g., flood, fire, theft) and technological obsolescence
(e.g., outdated software, inaccessible storage media). When a process unit is
dismantled or demolished, its productive “life” has ended, and the PHA records
can be discarded or retained in accordan ce with company policy. However, if the
process is merely shut down, decommissio ned, or “mothballed,” (even if they
have no plans to resume production), it is prudent to retain the PHA records.
Circumstances change, and years later there may unexpectedly be a need to
resume production. If the PHA records were kept, revalidation would be an
option; if not, an entirely new PHA would have to be completed before
production could resume. Even in ca ses where the process equipment is
ultimately dismantled and removed, access to PHAs could be of value to anyone
evaluating the hazards of remediation effo rts, which might be needed to allow
new construction at the site. |
342 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
Safeguards, Barriers, IPLs, and Other Layers of Protection
The concept of layers of protection was discussed in Section 14.7, Layer of Protection Analysis,
and illustrated in Figure 14.10. Over the years, there have been many terms used to describe
these layers including safeguards, barriers, and independent protection layers. Although these
terms sound similar, they do have different a ttributes as defined below and in Figure 15.5.
Layers of protection - Independent devices, systems, or actions which
reduce the likelihood and severity of an undesired event. (CCPS Glossary)
Safeguard - Any device, system, or action that interrupts the chain of
events following an initiating event or that mitigates the consequences.
(CCPS Glossary)
Barrier - A control measure or grouping of control elements that on its
own can prevent a threat developing into a top event (prevention barrier)
or can mitigate the consequences of a top event once it has occurred
(mitigation barrier). A barrier must be effective, independent, and
auditable. (CCPS Glossary)
Independent Protection Layer (IPL) - A device, system, or action that is
capable of preventing a scenario from proceeding to the undesired
consequence without being adversely affected by the initiating event or
the action of any other protection layer associated with the scenario.
Note: There are specific functional cr iteria for protection layers that
are designated as "independent." A protection layer meets the
requirements of being an IPL when it is designed and managed to
achieve the following seven core attributes: Independent;
Functional; Integrity; Reliable; Va lidated, Maintained and Audited;
Access Security; and Management of Change. (CCPS Glossary)
The term safeguard is a generic, all-encompassi ng term that is frequently used in HAZOPs
to capture all the potential layers of protection . The term barrier is more specific in that a
barrier prevents the incident or mitigates the co nsequences on its own. The term is used in
Bow Tie Analysis and this specificity supports the integrity of Bow Ties. The term IPL was
introduced in Section 14.7. It is even more prec ise which is required to support the integrity of
a Layer of Protection Analysis.
Many devices, systems, and actions are used to reduce process safety risk and can be
described by these terms. These are discussed in Section 15.4. |
182 | 5 Aligning Culture with PSMS Elements
com pany. Regulations are also considered by this element. While
not strictly standards, process safety regulations tend to be
developed and written as if they are standards, and some are
even referred to by that nam e.
Espousing a strong system of internal and industry standards
provides a framework for correct design, proper installation, and
effective inspection, testing and m aintenance. This is indicative of
positive safety cultures. The absence of standards, or inconsistent
application of standards is conversely an indicator of a weak
culture. If equipment is not designed to a form al code or standard,
how will you know it will m eet the process dem ands or how to
properly insect and test the equipment?
B y determining which standards are applicable and
understanding how they work, com panies can leverage
experience in designing and operating processes and
m anagement systems, while complying with applicable
regulations. Companies should keep abreast of new
developments in standards and regulations, and address changes
appropriately in its technology and m anagement systems.
Additionally, standards developed for different industry sectors or
even countries should be considered if they address challenges in
the facility’s sector. The American Petroleum Institute’s RP-755
addressing fatigue management is an excellent exam ple of a
standard with broad usefulness outside the US petroleum sector.
Establishing and maintaining internal corporate standards is
an effective way to keep abreast with developments in standards
and interpret these standards applicable to com pany technology
and culture. Some companies will implement internal standards
at the facility level to explicitly address local and national
standards. Others will strive to have one set of corporate
standards that applies regardless of location. This is largely a
m atter of preference. The im portant thing is that it is considered
part of the imperative for process safety to identify, understand,
and im plement the applicable standards. |
495
Table E.3 continued
Notes:
1. It is recognized that threshold quantities given in kg and lb or in lb and bbl are not exactly equivalent.
Companies should select one of the pair and use it consistently for all recordkeeping activities.
2. Refer to guidance on selecting the correct Threshol d Release Category and the use of Material Hazard
Classification Option 1 and Option 2.
Table E.4. Examples fo r material categories
Category Example Material
1 Br, HCN, Phosgene
2 BF 3, Chlorine, H 2S
3 HCl, HF, SO 2
4 Ammonia, CO, EO
5 Acetylene, Ethylene, Vinyl Acetate
Monomer, Aluminum Alkyls
6 Vinyl Acetate Monomer, Benzene,
Cyclohexane
7 Diesel, Mineral Oil, Muriatic Acid
Nonflammable/nonpoisonous gases
E.4 Classifying PSE Tier 1 and Tier 2 Events
The flowchart in Figure E.1 can be used to classify an LOPC as a PSE Tier 1 or Tier 2. APPENDIX E - CLASSIFYING PROCESS SAFETY EVENTS USING API RP 754 3RD EDITION |
202 | Appendix: Index of Publicly Evaluated Incidents
Section 1. RBPS Elements (Continued)
MOC—Primary Findings
A1, A2, A4, A6, A7, A10
C22, C22, C25, C31, C36, C47, C50, C51, C61, C63, C70, C72, C76
D9
HB5
J12, J24, J45, J55, J72, J86, J90, J94, J102, J106, J119, J132, J139, J167, J214,
J240, J255, J260, J264
S4, S7, S16, S17
MOC—Secondary Findings
C3, C7, C8, C62
J10, J14, J16, J26, J91, J111, J154, J205, J238, J239, J246, J250
S13, S14
Operational Readiness/PSSR—Primary Findings
C7, C11, C70, C76
HA10
J26, J40, J69, J90, J111, J146, J171, J174, J177, J178, J179, J183, J184, J188,
J189, J192, J213, J243, J246, J249, J263, J269
Operational Readiness/PSSR—Secondary Findings
D9
HA3, HA6, HB4
J23, J62, J103, J124, J147, J170, J185, J210, J212, J216, J217, J251
S5
Conduct of Operations and Operational Discipline—Primary Findings
A2, A5, A10
C3, C11, C12, C18, C26, C43, C50, C57, C58
D9
J2, J19, J28, J38, J49, J50, J51, J52, J53, J54, J55, J56, J57, J58, J61, J63, J67, J70,
J72, J73, J114, J127, J130, J147, J151, J165, J171, J174, J178, J180, J182, J183,
J188, J190, J192, J208, J209, J211, J217, J243, J247, J248, J259, J262, J270,
J271
S3, S4, S5, S13, S14
Conduct of Operations and Operational Discipline—Secondary Findings
A6, A7
C13, C15, C20, C24, C27, C28, C60, C76
D7, D19
J21, J22, J24, J25, J32, J35, J40, J64, J65, J75, J76, J91, J108, J109, J116, J119,
J128, J129, J131, J133, J162, J163, J170, J176, J181, J184, J185, J186, J212,
J237, J253, J261
S1, S10, S12, S15 |
APPLICATION OF PROCESS SAFETY TO ENGINEERING DESIGN,
CONSTRUCTION AND INSTALLATION 135
Inherently Safer Design
Trevor Kletz was an early proponent of inherent safety and CCPS formalized his
papers into books, initially in 1996, ag ain in 2009, and mo st recently into a
Guideline CCPS (2019a). These updates did not change the concepts but refined
the implementation examples. Some key words used to describe inherent safety
include:
●Minimize : Reduce inventories of hazardous materials
●Substitute : Replace hazardous material or pr ocess with a more benign one
●Moderate : Use less hazardous processi ng or storage conditions
●Simplify : Eliminate unneeded complexity a nd make designs error tolerant
Figure 7-2. Concept for includi ng inherently safer design
(Broadribb, 2010)
This figure incorporates ISD in a hierar chy of safety measures – with eliminate
hazards being the preferred option but fo llowed by reduced severity and reduced
likelihood options. Segregation uses la yout to separate hazards and reduce
escalation. Passive and active safeguards improve safety for people, but do not
address the inherent hazards of the process or the materials, instead mitigating their
potential consequences. The final measure, procedural safeguards, which is least
reliable, is the lowest category and it relies on personnel actions to reduce risk.
7.2.3 FEL-3
This stage takes the basic design from FEL-2 and refines it further. Earlier HIRA
studies (including PHA, ISD and CRA) ar e updated to reflect the greater design
detail available to ensure hazards have been identified, inherent safety principles
|
8 • Emergency Shutdowns 152
8.5.2 After the shut-down to different end state
However, if the emergency shut-down procedure results in an
abnormal equipment end state, such as rapid discharge of a reactor’s
contents to a temporary tank or other safe location, then the discharged contents should be safe ly handled and removed from the
affected process equipment or seco ndary containment before restart.
If the equipment’s condition is n ot evaluated before restart, and as
noted earlier, it is essential that everyone understands the final condition the equipment to ensure that it is prepared and ready before resuming start-up.
If a part of the facility goes in to a circulation or a standby mode
while other parts are shut-down, the hybrid operational state can be defined as a different end state , as well. Lessons Learned from
incidents that occurred when trou ble-shooting other possibly shut-
down parts of the process with oth er equipment placed into a standby
mode were illustrated in Chapter 7 (e.g., C7.6.1-1 and C7.6.2-1).
8.5.3 Addressing damaged equipment and processes after a
significant incident
If emergency shut-down procedur e or Emergency Shutdown Device
(ESD) causes damage to the equipment it is protecting due the consequences of not shutting the equipment down in the normal
manner, there should be a proced ure for addressing the equipment
damage before restart. Thorough tes ts and inspections, especially to
check for potential (or known) internal damage, should be performed before the equipment is restarted. Th us, it is essential that everyone
understands the final condition the eq uipment, that the equipment is
assessed for potential damage, and that the equipment is repaired, if needed, before resuming start-up. |
Piping and Instrumentation Diagram Development
164
and it is coned because of the higher weight of the tank
walls, as was mentioned before. The selection of floor cone‐down angle is a process decision to facilitate mate-rial movement toward the center. The floor cone‐down angle could be limited because of construction implica-tions. Generally speaking wherever the tank has a larger diameter, it is more expensive to have a larger floor cone‐down angle. For large diameter tanks (possibly more than 5–10 m diameter) the floor cone‐down angle is generally kept below 5°. A rule of thumb that can give a guideline for the maximum allowable floor cone‐down angle – from a constructability viewpoint – is as follows:
SDmax. 30
where:
Smax. is the maximum allowable floor cone‐down angle
in degrees (°) and D is the tank diameter in meters (m).
However, there are some cases where the tank has a
large diameter and for process reasons it should be high angled. There are some solutions for that. For example in some clarifiers or thickeners the floor should be high to help directing the settled solids (sludge) toward the center and finally removing it. If the clarifier or thickener is a large diameter one, the slope is possibly limited to 5° or a value around that. A rake system can be implemented to sweep the settled sludge toward the center of the tank.
9.18 Container Arrangement
Containers could be in a series and/or parallel arrange-ment when they are used for unit operation or process units. As tanks are less likely used for unit operation or as process units, vessels are more commonly seen on P&IDs in series or parallel arrangements.
If a vessel is supposed to be used for holding (short
time) it is usually a single vessel.
If tank(s) are supposed to be used for storing material
(long term) it could be single in the majority of cases. However, they could be in multiple arrangements. This multiple arrangement could be neither parallel nor in series. The tanks could be connected to each other with a specific piping arrangement to provide flexibility for the operators to use them in series or parallel, depending on the case. Figure 9.34 shows such an arrangement.
9.19 Merging Containers
Sometimes containers are merged together to save money. There are at least three ways to merge contain-ers: complete merge, merge with volume dedication, and merge while keeping physical boundaries.
Complete merge is using one container for more than
one purpose. This can be done by replacing two or more containers with only one of the same or larger volume.
“Merge with volume dedication” has the same concept
as “complete merge” with only one difference. In this type of merge the volume of the container is “somehow” dedicated to each user or purpose.
For example in Figure 9.35 a single tank is used for
fire water AND plant water. By a specific internal arrangement the plant water is allowed only to use the
T ank “A”T ank “B”Exit from tank “B”
Exit from tank “A”
when it is in parallel
Figure 9.34 Tanks in parallel and series arrangements.
Figure 9.35 Dedication of tank water to fire water and to plant water. |
Piping and Instrumentation Diagram Development
222
12.7 PRD Structure
The earliest type of pressure device was the one used
for steam engines in the 1900s. It was basically a plug that exerted force using a hanging weight to close the pressure‐releasing hole (orifice) and keep it close to the point that the pressure exceeds a specific value. The value of the pressure at which the device is intended to start to opening, or the “set pressure, ” could be adjusted by sliding the weight along the lever (Figure 12.4).
Principally speaking, every pressure/vacuum relief
device comprises three elements:
1)
A pre
ssure‐sensing element
2) A log
ic
3) An opening e
lement.
The pressure‐sensing element senses and monitors the
pressure of the enclosure and reports to the logic. The
logic decides if/when the pressure exceeds a pre‐set pressure, or set pressure, and sends orders to the open-ing element to open the device to enable the release of the excessively high pressure. In case of a vacuum, it can also “suck” from the outside of the enclosure to decrease (“break”) the vacuum in the enclosure (Figure 12.5).
Based on the fundamental concept of a PRD, all of
these elements must be mechanical and their communi-cation must be through mechanical links. Electrical, pneumatic, or hydraulic signals are not acceptable as communication routes in pressure/vacuum relief devices.
The above concept can be seen in the operation of a
pressure relief valve (PRV) in Figure 12.6.
12.8 Six Steps to Providing
a P
rotective Layer
There are six elements that should be considered during the design stage to make sure an optimal protective layer is provided.
These elements are:
1)
Lo
cating the PRD
2) Po
sitioning the PRD
3) Sp
ecifying the PRD
4) Se
lecting the right type of PRD
5) Se
lecting the right type of PRD arrangement
6) Che
cking the functionality of the PRD
We will discuss all of the above items except for items
3 and 4.
We briefly introduce “specifying PRD” because we
need to understand the technical information of PRDs Table 12.7 Codes in the pr essure relief device industry.
Code Code basisEnforcement agent
(approval authority)
US
(general)NB‐501,boiler and pressure vessel codeASME B&PV code NBBI (National Board of Boiler and Pressure Vessel Inspectors)
Canada (general)Safety codes CSA‐B51, ASME B&PV code A safety authority under the government:
TSSA, ABSA, etc.
Figure 12.4 Early t ype of pressure relief valve.
Pressure sensing element
LogicFully mechanical
Acting (opening) element
Figure 12.5 Fundamen tals of relief device operation.
Inlet connectionOutlet connection
Inlet connectionOutlet connection
Closed position Open position
Figure 12.6 PRV schema tic and operation. |
50 Guidelines for Revalidating a Process Hazard Analysis
Many view the HAZOP methodology as very deliberate and systematic in
structure but more time consuming when compared to the What-If/Checklist
method. However, experience shows that the time and effort required to
complete PHAs of comparable quality is driven more by the nature of the
hazards to be studied than by the choice of PHA technique. That is because PHAs
of comparable quality should include the same loss scenarios, identify the same
areas of elevated risk, and produce comparable recommendations for risk
reduction. In one study [33] published by the American Institute of Chemical
Engineers (AIChE), involving six different processes, a total of 414 meeting hours
were required when the PHA revalidations were conducted using the What-If
method, whereas 198 hours were required for the same six processes in the PHA
revalidations that occurred five years later using the HAZOP method. While it is
likely that several factors contributed to this productivity improvement, one
important factor was changing to the structured approach of the HAZOP
method. Focusing the teams’ attention on a discrete and organized catalog of
deviations was more efficient than having them develop and answer a randomly
ordered, long, and often redundant list of what-if questions.
It is important to note that the level
of detail applied to any PHA method (and
discussed further in Section 3.2.2) can
dictate whether its application is
appropriate. A skilled facilitator with
careful planning and a competent team
can complete a What-If/Checklist
Analysis that is more appropriate to the
process than a poorly conducted HAZOP
Analysis, and vice versa.
Assuming management is satisfied with the method and detail used by the
prior PHA team, the quality and completeness of the prior PHA should be judged
against the expected results from that method.
3.2.2 Level of Detail and Accurac y of the Core Analysis
What-If/Checklist. It can be more difficult to review the completeness of a
What-If/Checklist Analysis than other methods, depending upon the degree of
structure used in applying the What-If method. A reviewer can usually postulate
a question the team did not ask, and those questions can be addressed in an
Update . However, the Redo approach becomes attractive as the review discovers
more deficiencies, such as: Changing the Core Methodology
Changing the core methodology
(e.g., from What-If/Checklist to
HAZOP) for all (or a substantial
part of) the process almost
always invokes the Redo
approach. |
352 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
Other Incidents
This chapter began with a description of the Ce lanese Pampa, Texas explosion. Other incidents
relevant to risk mitigation include the incidents listed in Chapters 4, 5, and 6.
Exercises
List 3 RBPS elements evident in the Cela nese Pampa explosion summarized at the
beginning of this chapter. Describe their shortcomings as related to this accident.
Considering the Celanese Pampa explosion, what actions could have been taken to
reduce the risk of this incident?
Redundant instrumentation is an important de sign concept for improving the safety of
a system (e.g. airplanes, nuclear). Give two examples where redundant instrumentation
would have prevented a major chemical plant incident.
In a HAZOP, safeguards are identified that prevent or mitigate the consequences. In a
LOPA, IPLs are credited. How are safeguards and IPLs related?
How are SIS, SIL and IPL related?
Draw a swiss cheese model for the Arkema incident in 2017 as described in the CSB
investigation report (https://www.csb.go v/arkema-inc-chemical-plant-fire-/).
Draw a bow tie diagram for filling of a tank wi th a flammable chemical. The tank is filled
from a pipeline. The tank is fitted with a manual level gauge and a pressure relief valve.
The tank is located on the edge of facility near the main road.
Estimate the Probability of Failure on Dema nd (PFD) for a firewater sprinkler system
with failure rate of 0.1 failures/year and in spection interval of 2 years. Show your
results.
Estimate the Unavailability or Probability of Failure on Demand (PFD) for a flow
controller that is continually monitored with failure rate of 0.5 failures/year and mean
time to repair (MTTR) of 5 days. Show your results.
Table 15.1 lists some risk reduction measur es. These all cost money. How would you
determine which ones should be implemented in your design of a facility that handles
flammable materials?
References
API STD 520, “Sizing, Selection and Installation of Pressure-relieving Devices”, American
Petroleum Institute, Washington, D.C., www.api.org.
API 521 “Pressure-relieving and Depressuring Systems”, American Petroleum Institute,
Washington, D.C., www.api.org.
BowTie Pro, BowTie Pro Ltd., www.bowtiepro.com.
BowTieXP, CGE Risk Management Solutions, www.cgerisk.com
CCPS 2018, Bow Ties in Risk Management: A Concept Book for Process Safety , Center for
Chemical Process Safety, John Wiley & Sons, Hoboken, N.J.
CCPS Glossary, “CCPS Process Safety Glossary ”, Center for Chemical Process Safety,
https://www.aiche.org/ccps/resources/glossary . |
319
12.10 Hendershot, D.C., Safety through design in the chemical
process industry: Inherently safer process design. Presented at the
Benchmarks for World Class Safe ty Through Design Symposium,
sponsored by the Institute for Safety Through Design, National Safety
Council, Bloomingdale, IL, August 19-20, 1997.
12.11 Hendershot, D.C., Process minimization: Making plants
safer. Chemical Engineering Progress, 30 (1), 35-40, 2000.
12.12 Imperial Chemical Industries (ICI), The Mond Index, Second
Edition. Winnington, Northwich, Chesire, U. K.: Imperial Chemical
Industries PLC, 1985.
12.13 Mansfield, D., Malm en, Y. and Suokas, E., "The
Development of an Integrated Toolkit for Inherent SHE ." International
Conference and Workshop on Pr ocess Safety Management and
Inherently Safer Processes, Octobe r 8-11, 1996, Orlando, FL (pp. 103-
117). New York: American Institute of Chemical Engineers, 1996.
12.14 Palaniappan, C., Expert System for Design of Inherently Safer
Chemical Processes . Singapore: National University of Singapore, 2001.
12.15 Palaniappan, C., Srinivisan, R., and Tan, R.B.H., Expert
System for Design of Inherently Safer Processes, Ind.Eng. Chem. Res., 41,
6698-6722, 2002.
12.16 Renshaw, F. M., A major accident prevention program.
Plant/Operations Progress, 9 (3), 194-197, 1990.
12.17 Rogers, R.L., Mansfield, D. P., Malmen, Y., Turney, R.D., and
Verwoerd, M. The INSIDE Project: Integrating inherent safety in chemical
process development and plant design. In G.A. Melhem and H.G. Fisher
(Eds.). International Symposium on Runaway Reactions and Pressure Relief Design, August 2-4, 1995, Boston, MA (pp. 668-689). New York: American Institute of Chemical Engineers, 1995.
12.18 Rohm and Haas, 2000 EHS and Sustainability Annual
Report, Revised December 2002.
12.19 Shah, S., Fischer, U. and Hungerbühler, K., A hierarchical
approach for the evaluation of ch emical process aspects from the
perspective of inherent Safety. Tr ans IChemE, 81, Part B, November
2003. |
184 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
Containment by hedgerows and trees provided an elongated path for DDT.
Hedgerows near the pump house served as more congestion for the vapor cloud.
Also, a tree-lined street next to the facilit y caused further acceleration of the flame
front leading to detonation. That vegetation could do this, in effect acting like a pipe
rack or wall, came as a surprise.
Regarding detonations, the report, “Review of vapour cloud explosion incidents” (HSE
2017), has challenged the conclusion that the B uncefield explosion, and several others, were
detonations, based on the nature of some of th e physical damage at the explosion sites. It
hypothesizes that a mechanism in between a VCE and a detonation is possible, and the HSE
has called for more investigation of this phenom ena. Interested readers can obtain and read
the HSE report. For brevity, this book will conti nue to call the Buncefield and Jaipur explosions
detonations. The important thing to remember is that with these types of events the potential
damage can be much worse than the co mmon consequence models would indicate.
Lessons
Process Safety Culture . The atmospheric tank gauging (ATG) system became stuck (not
registering a level change) 14 times in the three months before 11 December. Each time it was
fixed by either the operators or the maintena nce crew. Sometimes the failure was not even
logged. The willingness to continue to operate with such an unreliable level control is indicative
of a poor safety culture and is an example of normalization of deviance.
Compliance with Standards. The land use planning standards in the U.K. assumed that
facility operators were in compliance with a ppropriate requirements. The MIIB recommended
using a risk-based approach to land use planni ng, requiring the operators to develop a risk
management plan.
Hazard Identification and Risk Analysis. Prior to this incident, the scenario that
occurred at Buncefield had not been considered credible. Since land use planning in the U.K.
was based on the worst credible case, the scen ario was not part of the Land Use Planning
process. Subsequently, guidance was published to update and improve standards at gasoline
storage depots.
Operating Procedures. The operating procedures were inadequate. The procedures
were not detailed enough (e.g. no safe operatin g limits, were included), and the supervisors
on each shift used the available level alarms differently.
Asset Integrity and Reliability. The IHLS failed to close the manual inlet valve because
the test lever was not secured. A safety critical de vice such as this switch not only needs to be
tested on a regular basis but needs to be put ba ck into service properly. The staff did not have
procedures for putting the switch back into oper ation. This led the HSE to issue an alert on
now to test the switch. The MIIB recommended that these storage sites improve their
maintenance systems and conduct regular proof testing.
Management of Change. In 2002 a large increase in throughput to the facility occurred
when an adjacent facility was shutdown. No MO C was done to see if the control systems and
staffing levels were adequate for the increase d throughput. The IHLS was installed in 2004. |
CONSEQUENCE ANALYSIS 309
Slade 1968, “TID-24I90: Methodology and Atomic Energy”, U.S. Air Resources Laboratory and
Division of Reactor Development and Tec hnology, U.S. Atomic Energy Commission,
Washington, D.C.
SuperChems, ioMosaic, https://www.iomosaic.com/service s/enterprise-software/process-
safety-office/superchems.
World Bank 1985, Manual of Industrial Ha zard Assessment Techniques , ed. P. J. Kayes, Office of
Environmental and Scientific Affair s, World Bank, Washington, D.C.
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114 | 8 Landmark Incidents that Everyone Should Learn From
town grew toward it, with an apartment complex, nursing home, and two
public schools built between 137 and 385 meters (450 and 1263 ft) away from
the West site. Zoning restrictions were inadequate considering the explosion
hazard presented by the ammonium nitrate the site handled and the potential
impact of an explosion (Figure 8.6).
Figure 8.6 Aerial View of West, TX, Site (Source: CSB 2016)
Ammonium nitrate is generally stable in its pure form at ambient
temperatures. However, when contaminated with organic materials and other
chemicals or heated, it becomes highly explosive. These properties have been
exploited by terrorists to make improvised explosive devices; in the past,
ammonium nitrate compositions were also used in military explosives. As a
result, ammonium nitrate is regulated by US Homeland Security and by safety
regulatory agencies in other countries. US OSHA and EPA regulations,
however, assume that ammonium nitrate in the workplace is in its pure,
ambient temperature form and it is not regulated by these agencies.
The company therefore treated ammonium nitrate no differently than
most of the other products it stored, without consideration of its potential
instability. The company did follow regulations for the anhydrous ammonia
tanks that were located at the site. This reinforces the idea that just following
regulations is not sufficient for process safety and that more information
needs to be considered.
As at Bhopal, neither the public nor the first responders had been told by
the company what to do in the event of an incident. Without the proper
training, first responders arrived on the scene unaware of the hazards of the
materials handled at the site and the procedures to handle such a fire. They
made the mistake of staying and trying to put out the fire; had they been
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CONSEQUENCE ANALYSIS 277
tank overfill and cascade of gasoline that ac ted like a waterfall with significant aerosol
formation, which led to a large vapo r cloud and subsequent explosion.
If the liquid released is superheated, during the flash a significant fraction of liquid may
remain suspended as a fine aerosol. Some of this aerosol may eventually rain out, but the
remainder will vaporize due to air entrained in to the cloud. In some circumstances ground
boiloff of the rainout may be so rapid that all the discharge may enter the cloud almost
immediately. In other cases, the quantity of liq uid may be so great that it cools the ground
enough to sufficiently reduce surface vaporization from the pool.
The flash from a superheated liquid released to atmospheric pressure can be estimated
in several ways. For pure materials, a pressu re enthalpy diagram or a thermodynamic data
table can be used. For liquids that are accelerated during the release, such as in a jet, a
common approach is to assume an isentropic pa th. A standard equation for the prediction of
the fraction of the liquid that flashes can be derived by assuming that the sensible heat
contained within the superheated liquid due to its temperature above its normal boiling point
is used to vaporize a fraction of the liquid.
For flashing mixtures, a commercial process simulator would normally be used as manual
treatment of multicomponent mixtures is time consuming.
Table 13.2. Input and output for flash models
Input Output
• Heat capacity
• Latent heat of vaporization
• Boiling point temperature
• Initial temperature and pressure The vapor-liquid split
Most evaporation models are based on the so lution of time dependent heat and mass
balances. Momentum transfer is typically ignored. These models rarely give atmospheric vapor
concentrations or cloud dimensions over the p ool, which may be required as input to dense
gas or other vapor cloud dispersion models.
Evaporation from liquid spills onto land is ty pically well defined as many spills occur into
a dike or other retention system that allows th e pool size to be estimated. Spills onto water
are unbounded and calculations are often empirica l. Vaporization from a pool is determined
using a total energy balance on the pool. The heat flux is the net total energy into the pool
from radiation via the sun, from convection and conduction to the air, from conduction via the
ground, and other possible energy sources, such as a fire.
The modeling approaches are divided into two cl asses: low and high volatility liquids. High
volatility liquids are those with boiling points near to or less than ambient or ground
temperatures. For highly volatile liquids, the vaporization rate of the pool is controlled by heat
transfer from the ground (by conduction), the air (both conduction and convection), the sun
(radiation), and other surrounding heat sources such as a fire or flare. The cooling of the liquid
due to rapid vaporization is also important. Th is approach seems to wo rk adequately for LNG,
ethane, and ethylene. The higher hydrocarbons (C3 and above) require a more detailed heat
transfer mechanism. This model also neglects possible water freezing effects in the ground, |
Subsets and Splits