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Piping and Instrumentation Diagram Development
322
This is a better arrangement when the horizontal cold
stream is a process stream and has another responsibility
downstream of this heat exchanger.
However, the temperature of the horizontal cold
stream is still changing and, if it is not tolerable, we can-not do anything for it in this heat exchanger.
We can have another variation of the arrangement in
Figure 15.56, by putting control valves on both the dis -
charge and bypass streams, as shown below.
We have already shown split‐range control of valves. In
order to maintain a constant flow rate when we have flow from both streams at the same time, we need to go with parallel control.
We could substitute the two control valves in
Figure 15.56 with a single three‐way valve, as shown in Figure 15.57.The disadvantage of using three‐way valves is that
they are not available in large sizes. They are also not suitable when they receive a stream with large
tem
perature variations. This will cause different rates
of expansion inside the valve, which inevitably leads to leakage.
One very interesting variation of bypass control is
shown in Figure 15.58.
In the arrangement shown in Figure 15.55, we have
a pressure differential controller (PDC) on the bypass line. If we have a situation where the pressure drop across the heat exchanger is large, most of the inlet flow will choose to go through the bypass line, where the pressure drop will be smaller. To avoid this, we can put in a PDC to control the pressure drop on the bypass line and thereby control the flow rate through that line.
The situation where it is a big advantage to use a
PDC on a bypass line is where you have a number of heat exchangers operating in parallel. If you didn’t use a PDC, you would have to have a bypass line with a control valve for each and every heat exchanger. However, if you use a PDC, you only need to install one bypass line across the whole bank of parallel heat exchangers, with one control valve.
TC
PARALLEL RANGETT
TE
Figure 15.56 Heat e xchanger bypass control with two control valves.When the fluctuation in temperature may be too great
for the equipment downstream, we can solve this by putting another heat exchanger in series with this one to control the temperature for downstream equipment.
The second heat exchanger must be a utility heat
exchanger.
TC TT
TEFigure 15.57 Heat e xchanger bypass control with a
three‐way valve. |
A.4 Report References | 219
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
J16 Leakage and Fire of Hydrogen from a Mounting Flange of a Safety
Valve in a Reactor at a Succinic Acid Manufacturing Plant (1998)
J17 Explosion of Coke Oven Gas During Cleaning at a Desulfurization
Regeneration Tower of a Coke Oven Gas Refining (1998)
J18 Fire of Xylene Remaining in Solid Piperazine Separated in a
Centrifuge (1998)
J19 Fire of Ethanol Caused Due to Air Intake in the Ejector of a
Treatment Drum at a Surfactant Manufacturing Plant (1998)
J20 Explosion Caused Due to Generation of a Combustible Gas-Air
Mixture at a Naphthalene Oxidation Reaction Plant (1998)
J21 Explosion of Acrylic Acid in the Drum Can in the Heating Cabinet for
Dissolution (1998)
J22 Damage to a Tank Roof Caused Due to Sticking of a Breather Valve
During Transfer of Raw Material (1998)
J23 Explosion of Silicone Products Dissolved in an Organic Solvent
During Subdivision Work (1997)
J24 Explosion in the Polycondensation Reaction of Benzyl Chloride
(1997)
J25 Ignition of Rubber Remained in the Reactor During Cleaning at a
Polybutadiene Manufacturing Plant (1997)
J26 Explosion of a Machine for Melting and Volume Reduction of
Polystyrene Foam (1997)
J27 Explosion and Fire Caused Due to Gas Leakage from High-Pressure
Ethylene Piping at an Ethanol Manufacturing Plant (1997)
J28 Explosion During Charging Operation of Raw Material Powder into
a Reactor Containing Dioxane (1997)
J29 Explosion of an Air Heater of a Boiler at an Agricultural Chemical
Manufacturing Plant (1997)
J30 Explosion of an Intermediate Concentration Tank at an Insecticide
Manufacturing Plant (1996)
J31 Explosion Due to an Incompatible Reaction in a Nitration
Workroom for TNT (1996)
J32 Explosion and Fire Induced Due to Incompatible Reactions of
Residual Contaminant at an Alkylaluminium Manufacturing Plant
(1996) |
Figure 15.10: Aqueous Ammonia Supply Proposal
The design team conducted a Haza rd and Operability analysis that
raised several concerns regarding the tank truck delivery system and
associated operations:
the risk of spills and operator erro rs for the tank truck portion of
the delivery system was higher for this option than an anhydrous
ammonia system
higher capital, operating and maintenance costs
the reliability of the addition of pumps in the system.
So, the project was recycled back to the option selection phase.
414 |
Table B.3. Generic Like lihood (L) Descriptors
Likelihood Short descriptor Description
1 Low Not expected to occur in life of
facility
2 Medium Possible to occur in life of facility
3 High Possible to occur in range of 1
year to 10 years
4 Very High Possible to occur at least once a
year
B.1 INHERENT SAFETY ANALYSIS – GUIDED CHECKLIST PROCESS
HAZARD ANALYSIS (PHA)
Table B.4 offers an example of a gu ided checklist approach. The analyst
asks the questions from the checklis t (potential opportunities) and the
team documents the potential conseq uences of any issue that may be
applicable to the process or node under study. Considering the four ISD
strategies, the team documents th e potential recomme ndations that
may address the concern ranked in the following order:
•First order ISD
•Second order ISD
•Layers of Protection 459 |
2.6 Understand and Act on Hazards and Risks |49
2.6 UN DERSTAN D AN D ACT UPON HAZARDS/RISKS
Flixborough, N orth Lincolnshire, UK, June 1, 1974
A vapor cloud explosion following the failure of temporary
bypass piping killed twenty-eight workers. M any other workers
suffered injuries and significant onsite and offsite property
damage occurred. The tem porary piping had been installed to
bypass the fifth oxidation reactor in a chain of six. Reactor five
had failed and was being repaired.
Supported only by conventional scaffolding, the tem porary
piping was installed without first Understanding and Acting Upon
the Hazards and Risks . Considering the haste to install the
bypass and the close spacing of work areas on the site, the
facility appeared to have a weak Sense of Vulnerability . After a
two-month exposure to stress, vibration, and fatigue, the piping
failed, creating a large release of flammable vapors.
The Flixborough incident hastened passage of the UK Health and
Safety at Work Act. While it predated the development of form al
PSMS elements as we know them, it rem ains a classic example of
failures of the Management of Change (MOC) and HIRA/PHA
elem ents. B oth elements rely heavily on dedication to
understanding hazards and risks, and how they can change as the
process changes. Understanding hazards is also a key aspect of
the PSM S element “Competency” (see section 5.4).
Leaders should understand the difference between hazards,
risks, and the safeguards that are used to act on these hazards
and risks. The hazard of a m aterial is the harm it can inflict.
Process hazards include toxicity, flam mability, reactivity, high and
low pressure, and high and low temperature. Physical impact,
electrical shock, and suffocation m ay also be process hazards. |
190 INVESTIGATING PROCESS SAFETY INCIDENTS
9.5 HYPOTHESIS TESTING
The following discussions are intended as an introduction to some special
techniques used by experts for technical analysis of evidence and hypothesis
validation. Novice investigators and individuals who are not experts in these
fields should be cautious when applying these tools. For most minor
investigations, review and application of the information in this section is
adequate for the investigation team to analyze the data. However, if legal
concerns arise during an investigation, ex perts in the forensic analysis of data
should be used to ensure a proper an alysis has been performed and correct
interpretation of the data has occurred.
9.5.1 Engineering Analysis
In addition to physical analytical me thods, engineering analysis tools and
methods are also useful during inciden t investigations. Engineering analysis
refers to calculations that can be performed to investigate and test various
hypotheses. Examples of engineering analyses include:
Forces
Stresses
Fluid motion and pressure
Heat transfer/temperature
Thermodynamics/en ergy transfer
Mass transfer and balance
Mass of process fluids and process equipment
Concentration of fluid in process equipment
Flow rates of fluids through process equipment and through
release points
Change in levels of tanks over time
Rates of chemical reactions
Dispersion of a gas
Investigators use engineering analys is methods to test the various
hypotheses that are put forth duri ng the investigation. Often rough
calculations may be all that is needed to determine if a hypothesis is possible.
For example, even if the entire conten ts of a tank are released, the volume
may not be sufficient to cause an overflow in another part of the process. A simple calculation may be sufficient to eliminate certain hypotheses that have been proposed. |
262
document the reasons why items were not considered, for
example, if they were not applicable or had been considered previously.
Documentation of rationale for rejecting potential IS opportunities (cost, creation of other safety or operability problem, etc.).
Recommendations/action plans for further evaluation or
implementation of IS alternatives identified during the study.
If the IS review was conducted as pa rt of a larger study (i.e., PHA or
hazard review), this information shou ld be incorporated into the report
of this activity. It is recommended that this information becomes a part
of the permanent process safety file and be maintained for the life of the
process. Electronic versio ns in an editable format (i.e., MS Word) should
be maintained to facilitate futu re updates and revalidations.
The rationale for why recommenda tions from IS reviews were
rejected should follow the followi ng guidance, which includes for
declining recommendations from inci dent investigations and process
hazards analyses:
The analysis upon which th e recommendations are based
contains factual errors.
The recommendation is not necessary. For example, the safeguards may be inadequate, but the consequences are operational, or the consequence or severity of the scenario
would not result in a significant release.
Another IS alternative would prov ide a sufficient level of hazard
reduction. (NOTE: Implementing only one option to address
identified hazards may not be ad equate to address the greatest
hazard reduction or elimination. However, it is not necessary to implement more than one IS altern ative if the implementation of
a second IS alternative does not add any significant hazard
reduction or has been documented as not feasible.)
The recommendation is not feasible due to one or more of the reasons listed below:
oThe recommendation is in conf lict with existing federal,
state, or local laws. |
38 Guidelines for Revalidating a Process Hazard Analysis
3.1 PRIOR PHA ESSENTIAL CRITERIA
3.1.1 Prior PHA Methodology Used
The prior PHA methodology refers to its core methodology and any
complementary analyses as discussed in Section 1.2. Aside from policy or
regulatory demands, two ke y questions should be considered when determining
whether the prior PHA methodology was appropriate:
1. Was the PHA methodology appropriate for the complexity of the
process?
2. Did the PHA methodology comprehensively identify the hazards of
the process, the engineered and administrative risk controls, and
the worst credible consequences assuming failure of all those
controls?
For example, PHA results comprised of only a short one-page checklist with
yes/no answers and related comments would be insufficient as a core
methodology for a PHA of a complex and hazardous unit involving reactions,
separations, and so forth. Likewise, an unstructured What-If Analysis only
identifying loss scenarios where the team had a concern or recommendation
would generally be considered inadeq uate as a core PHA methodology.
However, a thorough What-If Analysis co mbined with equipment- or process-
specific checklist analyses might be an appropriate PHA methodology for some
processes.
Under most circumstances, a PHA including a properly applied and fully
documented HAZOP as the core methodology will identify the process hazards,
risk controls, and consequences of failure of the controls for each section of a
process. A PHA structured with a well-organized and fully documented What-
If/Checklist Analysis using appropriat e process- and equipment-specific
checklists can also accomplish these objectives. For processes involving
compressors, centrifuges, or highly automated systems, an FMEA can be
conducted and documented in a manner that meets these objectives.
Any of these core methodologies ca n, by themselves, be applied and
documented in a manner that identifies process hazards, risk controls, and
consequences of failure of the cont rols. However, the most comprehensive
PHAs also include complementary analyses, and these are often in the form of
checklists. |
320 | Appendix E Process Safety Culture Case Histories
between the com pany incident com mand and the local
emergency response agency confused emergency response
organizations and delayed public announcements on actions that
should be taken to m inim ize exposure risk.
In m anaging the crisis, the com pany reported that “no toxic
chem icals were released because they were consumed in the
intense fires.” While a reasonable assum ption, investigators found
that air monitors placed near the unit to detect toxic chem icals
were not operational at the tim e of the incident, so this could not
be confirm ed. Managem ent also attempted to prevent public
access to inform ation about the accident by asserting that the
facility was covered by regulations related to sensitive security
information. This assertion was determ ined by the governing
authority to be without basis. Managem ent later acknowledged
that this was done due to lim it the potential outcry related to
existence of the highly toxic chem ical at the plant.
The investigators provided num erous exam ples of the
com pany using good engineering and operating practices to
protect against releases of the highly toxic chem ical, including
reducing inventory, locating the m ain storage tank underground,
shielding the above-ground day tank, and providing a dump tank
if necessary to rapidly em pty the day tank and associated piping.
And in fact, these procedures were effective and well-m anaged.
While investigators did not exam ine culture, readers can deduct
from the investigation report that the process safety culture
related to this unit was robust.
However, it is not clear that the PSM S and culture was
functioning as well in the adjacent unit. If the investigators had
exam ined culture, what potential culture gaps m ight the
investigators have considered exploring?
Did an extra high sense of vulnerability from the highly toxic
chem ical reduce com pany em ployees’ sense of vulnerability related
to other chem ical and processes? |
REACTIVE CHEMICAL HAZARDS 89
The owners did not do any reaction testing such as adiabatic calorimetry (e.g., Accelerating
Rate Calorimeter™ (ARC), Vent Sizing Package™ (VSP), Phi-Tec, or Automatic Pressure Tracking
Adiabatic Calorimeter® (APTAC)), although this type of testing had been good engineering
practice for years.
The CSB noted that process safety was not part of the chemical engineering curriculum in
almost 90% of universities at the time of the incident. In its report, the CSB recommended to
the AIChE and the Accreditation Board for Engineering and Technology, Inc. (ABET) that
awareness of reactive chemical hazards be part of the baccalaureate program (CSB 2009). This
recommendation was implemented by the ABET, in fact, the CSB notes that the action
exceeded the CSBs expectations.
Hazard Identification and Risk Analysis . Even though a design consultant
recommended that T2 do a Hazard and Oper ability (HAZOP) study on the process, T2
apparently did not do one. If the MCMT proces s had been reviewed by a competent PHA team
questions such as, “what happens if the temperatur e is too high?” or “what if the cooling fails?”
would have come up. These questions would le ad to recommendations such as: determine
what the safe operating temperature is, what ha ppens if it is exceeded, how can we make the
cooling system more reliable, or what othe r safeguards can be provided against high
temperature and pressure?
Asking these questions could also have led to a better understanding of the emergency
relief requirements. The emergency relief syst em (ERS) was based on the maximum rate of
hydrogen generation in normal operation (CSB 2009). The ERS was inadequate for the reaction
that occurred. After subsequent testing in a VSP, the CSB determined that the second
exothermic reaction was so fast that the re actor could not have been successfully protected
by a relief device. The only way to protect th e reactor from overpressuring was to vent the
reactor during the first reaction and allow the energy to be removed by boiling off the diglyme
solvent and MCPD.
Management of Change (MOC). After one year of production the batch size was
increased by one-third, without a safety revi ew. However, without the needed competency to
recognize reactive chemical hazard s, an MOC would not have helped.
Emergency Management. T2 did not warn emergency responders of the presence of
MCMT on site. MCMT is toxic by inhalation and skin contact.
Incident Investigation. Prior to the explosion, there had been unexpected exotherms in
three of the first ten batches during the first re action step when the pr ocess was scaled up to
the main reactor. After the first exotherm (in Batch 1), the response wa s to adjust the batch
recipe and to add cooling to the operating pr ocedures. Uncontrolled exotherms also occurred
in Batches 5 and 10. Nevertheless, after Batc h 11, the process scale-up was considered
successful. The owners did not recognize that the previous exotherms were actually near
misses which could have had more severe consequences, and therefore failed to further
investigate the causes of these exotherms.
A video about the T2 Laboratories explosion can be found on the CSB website at
http://www.csb.gov/videos/ . |
286
Employing the state-of-the-art in the design of the processing
technology is also a use of Substitution and Moderation , both in the
process engineering, as well as in the engineering of the equipment.
Keeping up-to-date on the state-of-the-a rt is an aspect of process safety
competency as it requires proactive activities to obtain and maintain
knowledge and expertise in the rese arch, development, and engineering
of the type of process technology in use. Also, in a basic sense, process
Simplification should result in less required trainingBTMBZFSTPG DPNQ
lexity are removed fr om the process, less IVNBOJOUFSGBDFJT SFRVJSFE
and the hu man interface that is required is TJNQMFS
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and easier to operate.
11.10 MANAGEMENT OF CHANGE / OPERATIONAL READINESS
Management of Change and Operational Readiness (or Pre-startup
Safety Review as it is often referred to) are often combined elements by
organizations in the same overall MO C procedure in PSM programs, with
the OR/PSSR one of the last steps in the MOC process. These elements
offer several ways to incorporate the four IS strategies. First and
foremost, MOC is required to be used whenever IS changes to existing
equipment are being proposed. However, the reverse should also be true, that is, whenever a change is being contemplated to existing equipment, the MOC process should in clude IS considerations. This is
just as important as looking for IS opportunities while processing a MOC for other reasons. The use and consider ation of IS strategies should be
incorporated into the identification of prospective changes and their
technical basis, the MOC safety and hazards reviews or PHAs conducted to examine the potential process safe ty impacts of prospective changes,
and the modification of operating an d other procedures pursuant to a
change. In particular, the safety review of the proposed change can employ checklists with IS questions similar to what has been described
for PHA/HIRA above. The four IS strategies should also be included in MOC/PSSR procedure checklists. The overall MOC process and where IS
guidewords and checklists can be used in it is shown in Figure 11.3 (Ref
11.16 Kletz 2010). Table 11.2 shows a list of MOC questions that can be used when reviewing proposed chan ges. As with Process Knowledge
Management, the use of IS strategies a n d c o n c e p t s i n a d e s i g n o f a
process should be clearly document ed because they are inherent and |
380
14.2.4 Safer Technology & Alternatives Analysis – Revised US EPA Risk
Management Program (RMP) Rule
This final section on specific Un ited States regulations with IS
requirements focuses on the 2018 the U.S. Court of Appeals for the DC
Circuit decision to vacate the de lay of the final revised RMP Rule
published in the Federal Register in 2017. The revised RMP Rule contains
a provision to perform a Safer Technology & Alternatives Analysis (STAA)
as part of performing PHAs on RMP-covered processes.
US EPA modified the PHA provisions in the RMP Rule by adding a
requirement for certain industry se ctors to conduct a STAA and to
evaluate the practicability of any inherently safer technology (IST)
identified. The practicability study will determine the costs and assess
the reasonableness of implementing technology alternatives. US EPA
limited the applicability of this requ irement to owners or operators of
facilities with RMP Program 3 regulated processes in North American Industrial Classification System (NAICS) codes 322 (paper manufacturing), 324 (petroleum and coal products manufacturing), and 325 (chemical manufacturing). In the proposed rulemaking, US EPA specified that the STAA would cons ider, in the following order of
preference:
IST or inherently safer design (ISD),
Passive measures,
Active measures, and
Procedural measures.
US EPA further indicated that the owner or operator would be able
to evaluate a combination of th ese risk management measures to
reduce risk at the process. US EPA did not mandate the adoption of any
IST found to be practicable in part because we recognize that a passive
measure or other approach on the ST AA hierarchy may also be effective
at risk reduction and left the adoption of particular accident prevention
approaches to owners’ and operators’ reasonable judgment.
US EPA also added several definition s that relate to an STAA. US EPA
defined active measures to mean risk management measures or
engineering controls that rely on me chanical, or other energy input to
detect and respond to process devi ations. Some examples of active |
15. Worked Examples and Case Studies
15.1 INTRODUCTION
This chapter illustrates the application of IS principles and concepts in
both idealized and actual situations. It also includes a post hoc
consideration of IS opportunities as applied to the Bhopal tragedy,
dramatically illustrating the potential benefits to both the facility and the
surrounding community from identifying and implementing IS
opportunities.
15.2 APPLICATION OF AN INHERE NT SAFETY STRATEGIC APPROACH
TO A PROCESS
As discussed in Chapter 8, inherent safety (IS) concepts can be
considered throughout the life cycle of a process. The following example
illustrates the concepts described in Chapter 2 (see Figure 2.3), as
applied over the life cycle of a process.
Reactive Chemicals, Inc., a fictiona l coatings industry supplier, is
planning to install a new polymeriza tion unit to produce Intermediate C
and Final Product Z. The final product goes into various coatings industry
applications. Industry expectations ar e for lower solvent formulations of
this type polymer. The following illustrates the processes involved:
Intermediate production: A + B = C
In the intermediate reaction, raw material A is reacted with raw
material B to produce intermediate C. Current production is in a batch
reactor with all materials, including the catalyst, in the initial charge.
Raw material A is flammable (flash point <100ºF), toxic, and supplied
and stored in bulk. Raw material B is a reactive monomer that is
corrosive (to human tissue) and combustible (flash point >100ºF) and is
typically inhibited with hydroquinone (HQ) or methoxyhydroquinone
(MEHQ). Like Raw Material A, it is supplied and stored in bulk. The
catalyst used for the intermediate pr oduction is boron trifluoride (BF3),
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56 INVESTIGATING PROCESS SAFETY INCIDENTS
responsibility a corporation assumes once it has increased knowledge of a
hazard or remedy. Failure to act on this knowledge may result in much more
significant legal and regulatory consequences.
The management system can include actions for companies to take
when preparing for an agen cy inspection. Whether or not to consent to an
immediate entry by govern ment inspectors in the aftermath of an incident
is a difficult question to answer in any situation. It is impossible to answer
generically. Consider involving legal co unsel in these situations. Remember
that the incident site and evidence may come under regulator control.
Facility managers should be aware of the company’s righ ts with regard to
unreasonable searches and seizures. A governme nt entry into and search of
a facility in the wake of an incident may be unreasonable. It may be
appropriate to refuse to consent to entry in some cases. In others, it may be appropriate to consent to the government entry
under specific conditions.
The conditions might include limits on the scope and duration of the
inspection or specific agreemen ts about the taking and sharing of
photographs and interviews of employees . Of course if the visitors have
one, the terms of a government agency warrant must be followed. In general,
cooperating with an agency seeking to perform an investigation is the best
approach. In the long term, this appr oach can help forge a good working
relationship wi th the agency.
Whether or not the agency is admitte d to the facility by the consent
of the facility or under a warrant, the agency’s purpose should be kept in
mind. That purpose may not be the same as that of the company incident
investigation team. The company seeks to identify the factors contributing to
the incident and the underlying causes . The agency also seeks to identify
regulatory violations and evidence that may lead to an enforcement action. A regulator’s approach to incident investigation has to be different from the company’s as “proof beyond a reas onable doubt” is required if a
criminal
case is justified. Of course, both parties want to ensure that lessons are learned to prevent future incidents. Especially
when an accident causing death or
personal injury has occurred, government investigators are likely to assume
that a preventable condition caused the incident, that the condition violated
a statute or regulation, an d that regulatory penalties should be imposed.
Agency involvement presents challen ges from the facility’s perspective.
Facility personnel need to manage the incident and its aftermath, but may
a l s o b e a s k e d t o d i v e r t resources to accommodate agency personnel.
Personnel should cooperate with authorities but should avoid volunteering unnecessary or unconfirmed information. Plant staff may be asked |
7. Developing content of a job aid 73
A common approach to engaging oper ational and maintenance staff in
developing procedures for existing tasks is to conduct a walk-through or a talk-
through, possibly aided by a video recording of the task.
It can help to use a questionnaire to assi st with the production of the job aid or
procedure. This should include questions, w i t h p r o m p t s o r s u g g e s t i o n s t o h e l p
encourage information sharing, and to ca pture details about the task. It should
also be used to record responses duri ng the walk-through, to capture detailed
information about the task steps. An example process is provided in Figure 7-3.
The Human Performance Oil and Gas (H POG) group also provide a Walk
Through Talk Through template and guide [ 35]. This is a free resource that also
covers capturing task steps, potential errors and ideas on error prevention.
In the case of new processes, tasks ca n be viewed or imagined by use of
process flow, functional, instrumentation diagrams and/or 3 dimensional models.
If available, drawings or mo ck-ups may b e used to help identify task s and sub-
tasks.
Some important information that can be realized or obtained from a walk-
through are 1) assumptions or preconditi ons assumed when starting the task, 2)
opportunities for errors, and 3) possible different ways of doing things. Task walk-through
The walk/talk-through approach is a simp le process that consists of a person,
with knowledge of a task, demonstrating how it is done, while being observed
by someone else.
It should be a fair and accurate refl ection of how the task is actually
performed. A task walk-through should be completed prior to first use of a
procedure. |
62 INVESTIGATING PROCESS SAFETY INCIDENTS
note, email, report or communication as if it would become a public
document available to the press, go vernment or the public in general,
including competitors. Regulatory requ irements may dictat e that reports on
process safety are to be shared with workers, depending on jurisdiction
and type of incident.
Other protections that may apply include The W ork Product Doctrine and
The Self- Critical Analysis Privilege (Adams, 1999). The work product doctrine
was created to protect materials prepared in anticipation of litigation from
discovery. Although technically speaking a lawyer might no t have to be
involved for material to acquire work product protection, atto rneys may need
to be involved for several reasons. First, some rulings have favored the
involvement of a lawyer. Second, involving a lawyer suggests the matter
should not be considered ordinary course of business. Third, the lawyer’s
involvement emphasizes that the work is being done in anticipation of
litigation.
4.2.3.2 Recording the Facts
There may be a perceived conflict between the need of the investigation
team to gather information quickly and record observations versus the
legal risk the company could face fr om hastily prepared notes or erroneous
preliminary conclusions. Haste in making notes without clearly distinguishing between factual
observations and speculation can cause
unnecessary legal risk to the company. The company could spend a great deal
of time and money trying to explain the hasty notes in litigation or
enforcement actions. The investigation team should take accurate notes
and record only facts. Any opinions or speculation should be clearly noted
as such. Facts cannot be altered, but conclusions can change as the
investigation continues. In some cases, the legal counsel should review
documents that are prepared by the investigation team for outside
distribution as well as the final offici al reports as they are drafted. The
guidance by legal counsel can help to limit unnecessary liability. Typical
guidance to investigators regarding note and report writing may include:
• Using header and footer designation s to identify official incident
team internal documents. Lega l counsel may recommend adding
statements such as, “Privileged and Confiden tial—Attorney–Client
Privileged Information” or other designators on each page of
certain documents
• Refraining from use of superlatives and inflammatory language;
rather, use factually accurate statements
• Refraining from use of judgmen tal words with special legal |
Event: First European Conf. of Young Res. Chem. Eng , July 14-18, 1996
(pp.62-64). Rugby, UK: Institution of Chemical Engineers.
Edwards, D.W., Lawrence, D. , and Rushton, A.G. (1996).
Quantifying the inherent safety of chemical process routes. In 5th World
Congress of Chemical Engineering , July 14-18, 1996, San Diego, CA (Paper
52d). New York: American Instit ute of Chemical Engineers.
Eierman, R. G. (1995). Improvin g Inherent Safety With Sealless
Pumps. In E.D. Wixom and R.P. Benedetti (Eds.). Proceedings of the 29th
Annual Loss Prevention Symposium , July 31-August 2, 1995, Boston, MA
(Paper 1e). New York: American Institute of Chemical Engineers.
Emsley, J. (12 March, 1994). A cleaner way to make nylon. New
Scientist , 15.
Englehardt, J. D. (1993). Pollution prevention technologies: A
review and classification. Journal of Hazardous Materials, 35, 119-50.
Englund, S.M. (1990). Opportunities in the design of inherently
safer chemical plants. Advances in Chemical Engineering , 15, 69-135.
Englund, S. M. (1990). “The design and operation of inherently
safer chemical plants.” Presented at the American Institute of Chemical
Engineers 1990 Summer National Meeting, August 20, 1990, San Diego,
CA, Session 43.
Englund, S. M. (1991a). Design and operate plants for inherent
safety - Part 1. Chemical Engineering Progress , 87 (3), 85-91.
Englund, S.M. (1991b). Design and operate plants for inherent
safety - Part 2. Chemical Engineering Progress , 87 (5), 79-86.
Englund, S.M. (1993). Process and design options for inherently
safer plants. In V. M. Fthenakis (ed.). Prevention and Control of Accidental
Releases of Hazardous Gases (9-62). New York: Van Nostrand Reinhold.
Englund, S. M. (1994). “Inherently safer plants—Practical
applications.” Presented at the American Institute of Chemical
Engineers 1994 Summer National Meet ing, August 14-17, 1994, Denver,
CO, Paper No. 47b. 476 |
EVIDEN CE ANALYSIS & CAUSAL FACTOR DETERM IN ATION 179
determining the cause of loss of containment that led to a flammable
material release and fire.
Figure 9.1 Scientific M ethod Process
Data collection is the second step of the Scientific Method process. This
includes examination of the scene, measuring and documenting damage,
interviewing witnesses, and data collection activities, as described in
Chapters 7 and 8.
The collected data are anal yzed in the third step. Analysis refers to all
manners of evaluating data, including examination and testing of physical data, engineering calculations, sy stems testing, simulations, and
reconstructions as described in this chapter.
Observations, measurements, data analysis and other information are
used to formulate hypotheses in the fourth st ep. Hypothesis formulation is
inductive reasoning. It is important to recognize that inductive reasoning
involves postulating a reasonable conclu sion from the available data, but the
conclusion may not necessarily be true. For example, it may be hypothesized
that a pipe burst because the internal pressure exceeded the pipe’s pressure
capacity. However, it remains to be proven that the pipe failed due to
excessive pressure rather than corros ion, a material defect, some other
cause, or a combination of factors.
It may appear to be unproductive to postulate hypothes es that may not
be true. However, during the course of an investigation, data may not be
available to prove or disprove a hypothes is at the time that a hypothesis is
postulated. By postulating the hypoth esis, investigation activities can be
developed to evaluate the hypothesis, such as metallurgical examination of
|
6 • Recovery 105
processes, as was illustra ted in Figure 3.2 and Figure 3.3, respectively.
An abnormal situation is defined as “a disturbance in an industrial
process with which the Basic Proces s Control System (BPCS) of the
process cannot cope” [34]. The recove ry efforts to control successfully
the process safety risks depend on the integrity and reliability of the
engineering controls and on operational discipline from those responding through the admi nistrative controls [21].
Since relatively “small” process deviations are expected, they can
be successfully responded to, as is illustrated for a co ntinuous process
in Figure 6.3’s timeline. The process deviations can be anticipated and
determined beforehand using the hazards and risks analysis approaches, as discussed briefly for a higher pressure deviation in
Section 6.3. Then, with the under standing of the deviations with
process safety risks that should be managed, the engineering and
administrative controls required for normal operations can be
identified, designed, implemented, and maintained. These controls help the operations team safely re turn the process to its standard
operating conditions once the deviations are detected. Engineering controls include understanding the dynamic characteristics of the
Basic Process Control Sy stem (BPCS) [59]. The administrative controls,
the procedures for “normal operations” are written to guide the operations team on the standard (e xpected) operating conditions and
often provide minimal troublesh ooting protocols to help with the
recovery efforts. As was noted earlier in this chapter, when the recovery efforts for an abnormal situation are unsuccessful, then the
operations team will shut the process down. |
PROCESS SAFETY AND MANAGEMENT OF ABNORMAL SITUATIONS 11
process hazards to aid managing abnormal situations (CCPS 2007a,
2015, 2011a),
Asset Integrity and Reliability to ensure that process equipment
and control systems remain fit for purpose and reliable throughout
their life to minimize challenges to protection layers (CCPS 2007a,
2017a, 2017c, 2007b),
Conduct of Operations and Operational Discipline to ensure
that all tasks including those e ssential for safe operation are
performed reliably to minimize errors leading to abnormal
situations (CCPS 2007a, 2011b, 2018f),
Process Safety Culture to maintain the values and behaviors of a
sound culture to deliver safe operations and improve human
factors to help provide the conditions that support maximum
performance of workers during abnormal situations (CCPS 2007a,
2018c, 2006, 2004), and
Incident Investigation to learn from experience of prior abnormal
situations and take action to strengthen management systems and
process control to avoid and/or mitigate future abnormal situations
(CCPS 2019).
Application of these and other process safety elements for managing
abnormal situations is discus sed in detail in Chapter 3.
2.2 THE CASE FOR POSITIVE MANAGEMENT OF ABNORMAL
SITUATIONS
An abnormal situation typically starts with one or more operating
parameters drifting outside normal limits that may impact product yield
and quality. However, if this cond ition is not managed positively and
quickly, the situation can rapidly escal ate to a more dangerous and costly
event that may include downtime, lo st production, equipment damage,
or injuries, as well as external prop erty, environmental, and reputational
damage.
Figure 2.2 (BakerRisk 2021) illustrat es the concept of operating limits,
showing the deviation of an oper ating parameter from “normal”,
through a “troubleshooting” zone, in to an “emergency” zone. Once the |
TOOLS AND METHODS FOR MANAGING ABNORMAL SITUATIONS 145
Example Incident 5.4 – Flight 173 DC-8 Crash in Portland, 1978
(cont.)
The NTSB considered th at the accident was an example of a recurring
problem:
“… A breakdown in cockpit management and teamwork during
a situation involving malfunctions of aircraft systems in flight .”
The report continued:
Admittedly, the stature of a captain and his management style
may exert subtle pressure on his crew to conform to his way
of thinking. It may hinder interaction and adequate
monitoring and force another crewmember to yield his right
to express an opinion. The first officer’s main responsibility is
to monitor the captain. In particular, he provides feedback for
the captain. If the captain infers from the first officer’s actions
or inactions that his judgment is correct, the captain could
receive reinforcement for an error or poor judgment.
The final recommendation in the NTSB report was as follows:
“Issue an operations bulletin to all air carrier operations
inspectors directing them to ur ge their assigned operators to
ensure that their flight crews are indoctrinated in principles of
flightdeck resource management, with particular emphasis on
the merits of participative management for captains and
assertiveness training for other cockpit crew members.”
The investigation led to the development of assessment and training
on Crew Resource Management (CRM). Today, CRM has evolved to cover
many issues that are highly relevant to the management of abnormal
situations. Outside the aviation indu stry, it is sometimes called Team
Resource Management (T RM) or Non-Technical Sk ills (NTS, or NOTECHS).
It can be defined as “ the cognitive, social and personal resource skills that
complement technical skills, and contribute to safe and efficient task
performance ” (Flin et al 2003). It primarily focuses on leadership
techniques and effective management of resource s, but also concerns
the cognitive skills that are required to gain and maintain situation (or
situational) awareness, particular ly in stressful situations. The
International Association of Oil an d Gas Producers (IOGP) produced a |
334
reduced - that the increased probab ility of a release of less hazardous
materials presents a lower risk than a lower probability of release of a
higher hazard material.
Another example of potential shifts, rather than reductions in risk is
the question of whether converting from chlorine gas to bleach shifts
risk from the population around th e water treatment facility to the
facility producing the bleach. If the bl each supplier also supplies chlorine
gas by taking large quantities of chlorine and repack aging them into
smaller containers, then the facility may be able to readjust the amount
of chlorine from repackaging to bl each production. However, a bleach
supplier that does not repackage chlo rine may be required to increase
the amount of elemental chlorine used at that facility in order to meet
the increased demand for bleach. If th e bleach supplier is also in a more
densely populated area, the increase d chlorine needed at the facility
could increase the risk to that new population. Again, the question of whether overall risk is reduced or shifted will depend on the specifics of an individual water treatment plant, as well as the specifics of the treatment plant’s supplier (Ref 13.26 Overton).
13.5 INHERENT SAFETY AND ECONOMIC CONFLICTS
13.5.1 Existing plants – operationa l vs. re-investment economics in a
capital-intensive industry
The following example illustrates the selection of an inherently safer
design solution for an existing process.
The design problem was to avoid a significant leak in several water-
cooled heat exchangers. These exchan gers used material on the process
side that reacted violently with wate r, producing corrosive and toxic by-
products. Alternative solutions cons idered included combinations of
passive (double tube sheet or falling film exchangers), active (multiple
sensor leak detection with automa ted isolation), and procedural (a
variety of nondestructive testing/ in spection techniques, periodic leak
testing with inert gas, improved clea ning procedures) strategies. All of
these design alternatives resulted in a lower risk level than the original
design. However, none was totally acceptable (see Table 13.3). When
management studied the effort and commitment of resources
necessary to maintain a less than sati sfactory risk level, they chose a |
LESSONS LEARNED 351
Examples of old newsletters that still convey highly relevant learning T are
shown in the ICI newsletter (Kletz, IChemE website), in Figure 16.3 and Figure
16.4.
Figure 16.3 ICI Safety Newsletter No. 96/ 1 & 2
|
TOOLS AND METHODS FOR MANAGING ABNORMAL SITUATIONS 125
Table 5.4 Policies and Administrative Procedures
Common Tools
and Methods Strengths Weaknesses
Organizational
chain of
command,
hierarchy Defines responsibilities and
authorities Limitations of authority can
create problems in
abnormal situations when
critical decisions must be
made quickly.
At large facilities, area
management can devolve
into ‘kingdoms’ that result
in inconsistent standards
across the site.
Communications
between shifts –
verbal, written
logbooks and
electronic Provides seamless link
between shifts so that
transient conditions are
managed. In practice, the quality of
shift change
communications is highly
variable, and requires
supervisor monitoring.
Auditing of
conformance to
policies and
administrative
procedures. Can detect gradual
degradation of systems and
behaviors that may not be
apparent to people working
day-to-day. Can also detect
specific faults that would
aggravate an abnormal
situation. Findings are a snapshot in
time so that failings that
occur between audits may
be present for a year or
more before being
detected.
Process Metrics Key Performance Indicators
(KPIs) can be established to
monitor the alarm system
data as well as process
parameters.
Excellent for checking
current process conditions
against target parameters.
Similar metrics may apply
across multiple processes. May provide a superficial
view of “symptoms” rather
than underlying faults.
|
31
Independent protection layers (IPL ) that meet the prerequisites of
independence, effectiveness, an d auditability may be credited
qualitatively or semi-quantitatively in formal Layers of Protection
Analysis (LOPA) to determine if the co llective protective features (i.e., the
layers) are adequate to reduce the ri sk of an undesired hazard scenario
to a tolerable level. These are generally the most reliable and robust layers and may include safety instru mented systems (SIS), basic process
control systems (BPCS), relief devices, operator response to alarms, certain mitigation systems, and certain key design features related to preventing process safety incident s. Creating multiple layers of
protection, and those that qualify as IPLs, between a hazard and potentially impacted people, prop erty and the environment can be
highly effective. Their application ha s significantly improved the safety
and process safety perf ormance of the chemical /processing industry.
However, such an approach may have significant disadvantages:
The basic hazard(s) remains, and some combination of failures of
the layers of protection may re sult in an incident, thereby
allowing the consequences to be re alized. Every active or passive
layer has a certain likelihood of fa ilure, due either to mechanical
means or management systems failures, such as not
maintaining or keeping administ rative controls active. The
outcome of the event may be limited by whatever passive or inherent layers have been applied.
Potential impacts could be realized by some unanticipated route or mechanism . Hazardous event can occur by means beyond what
were anticipated by process sa fety engineers. Accidents can
occur by mechanisms that were unanticipated or that were poorly understood. Complicated and overlapping layers of protection increase the possib ility of unanticipated failure
routes, particularly when common cause failures are shared by some of the layers, i.e., they ar e not independent. Therefore, the
actual risk may be the same or even increase after the application of additional layers of protection. For example, a
complicated shutdown system may cause an inadvertent sudden shutdown, which presents an overpressure, leading to a release. |
136 | 4 Applying the Core Pr inciples of Process Safety Culture
proactive approach to process safety as well as other
environment, health, safety, security, and quality, and encourages
collaboration with regulators. This can help strengthen PSMSs and
contribute towards establishing the imperative for process safety .
Various country and regional programs led by regulators such as
OSHA VPP (USA), Safer Together (Australia), and Step Change in
Safety (UK) seek sim ilar goals.
The threat of a routine regulatory inspection is generally not
an incentive to im prove culture or PSM S perform ance. In general,
regulatory agency staffing levels are rarely sufficient to put teeth
in such a threat. Som e agencies have been trying to change this
by focusing on only 1-2 PSMS elem ents and certain sub-sectors,
such as the National Em phasis Program s (NEPs) used in recent
years by OSHA in the USA. Facilities leaders should take care to
prevent regulatory focus on just a few elem ents from leading to
normalization of deviance or loss of the imperative for process safety
in the other elements.
While some process safety regulators around the world are
them selves process safety experts, the majority are not. Their
backgrounds m ay be in occupational safety, environm ental
sciences, or sim ilar disciplines that enable them to interpret
regulations and understand management system s. In other
words, regulators will generally not conduct in-depth technical
analysis, but they will understand and evaluate management
system performance. They will also be sensitive to cultures that
do not take management systems perform ance seriously.
Regulators will certainly come to the plant following a m ajor
release incident. In such cases, regulators will generally have one
or more regulatory findings. Having a collaborative relationship
with the regulator while demonstrating a strong culture will help
limit findings by keeping the regulators’ focus on the relevant |
102 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
that jurisdiction. These codes are a good source of knowledge addressing fire protection and
suppression. Of note are the following. (NFPA)
NFPA 491M Manual of Hazard ous Chemical Reactions
NFPA43 B Storage of Organic Peroxide Formulations
NFPA 49 Hazardous Chemicals Data
NFPA 325 Fire Hazard Properties of Flamma ble Liquids, Gases, and Volatile Solids
NFPA 430 Storage of Liquid and Solid Oxidizers
Summary
Reactive chemical hazards can occur in a variety of industries and types of equipment.
Incidents occur when the reactive hazard is unk nown or when it is underestimated. Wherever
chemicals are handled and processed, even where it is not understood that reactive chemistry
can occur, the chemical properties should be understood, hazards screened, and safeguards
implemented.
Do not assume that the chemicals can be co ntrolled in all operating conditions at the
facility. If the data are not available to verify this, then conduct testing to gain the data. Many
sources are available to gather the chemical property data and useful tools such as the
Chemical Reactivity Worksheet can be used to analyze the hazards.
Other incidents
Other incidents involving reactive chemicals include the following.
Rohm & Haas Road Tanker Ex plosion, Teeside, U.K., 1976
Arco Channelview Explosio n, Texas, U.S., 1990
Hickson Welsh Jet Fire, Yorkshire, U.K., 1992
Hoechst Griesheim, Explosion, Frankfurt, Germany, 1993
Port Neal AN Explosion, Sioux City, Iowa, U.S., 1994
Napp Technologies Explosion, Lodi, New Jersey, U.S., 1995
Bartlo Packaging Pesticide Explosion, West Helena, Arkansas, U.S., 1997
Morton International Explosion, Paterson, New Jersey, U.S., 1998
Concept Sciences Hydroxylamine Explosio n, Allentown, Pennsylvania, U.S., 1999
AZF AN Explosion, Toulouse, France, 2001
Synthron Chemcial Explosion, Morg anton, North Carolina, U.S., 2006
Bayer CropScience Runaway Reaction and Pressure Vessel Explosion, Institute, West
Virginia, U.S., 2008
West Fertilizer AN Explosion, West, Texas, U.S., 2013
Tianjin AN Explosion, China, 2015
Arkema Fire, Crosby, Texas, U.S., 2017
Seveso Disaster, Seveso, Italy, 1976
Port of Beirut Ammonium Nitr ate Explosion, Lebanon, 2020 |
APPENDIX A – CONCLUDING EXERCISES 469
8. What inherently safer design options might be considered for this project?
9. Name three failures that might occur with this equipment.
10. A consequence analysis is to be performed. List 3 potential scenarios including source,
transport, consequence effects, and potential outcomes.
11. Draw a swiss cheese diagram for one of the scenarios identified in the HAZOP.
12. Suggest how human factors could be considered in conducting the HAZOP.
13. List 5 things you expect to be on the operational readiness plan for this project.
14. As the project is 50% through the detailed engin eering, a proposal is made to increase the
reactor size. How should this be handled?
15. List three operating practices and three safe work practices that would be appropriate for
this facility when it is operational.
16. List 3 emergencies should be addressed in th e Emergency Response Plan for this facility.
17. List 2 means to engage the workforce in the pr oject. List 2 stakeholder groups that should
be involved in the project.
18. List 3 leading and 3 lagging process safety metr ics that might be appropriate for this facility
when it is operational.
19. What action might you take to foster a g ood process safety culture on the project?
Exercise 3: Ethylene Buffer Tank
An operator is preparing an outdoor ethylene buffer tank for maintenance by evacuating the
vessel of ethylene to an acceptable level. While lining up the vessel vent line to a flare header,
an ethylene release to atmosphere occurred du e to a ¾” bleed valve being inadvertently left
open.
When you arrive at work, your boss has several questions regarding the incident, and has
given you 80 minutes to give him the answers. The first thing you do is gather the process
safety information related to the incident from the Cameo database, MS DS, and CRW. This is
given in Table A.2.
|
KEY RELEVANCE TO PROCESS PLANT OPERATIONS 79
3.4.3.2 Issues Associated with Various Chemical Phases
Several major industry events have occurred because of personnel not
understanding or addressing that an abnormal situation is developing at
the interface between different phases of a chemical mixture. Most often
this is simply a case of a faulty instru ment (e.g., level transmitter failure).
However, in other cases, the instrume nt may be performing correctly but
the resulting output is not reflecti ve of the actual situation due to
transient conditions. Examples of ea ch are provided in Example Incident
3.18 and Example Incident 3.19.
Example Incident 3.18 - Unre liable Interface Detector
In a hydrofluoric acid (HF) alkyla tion unit, the interface detector
between the HF and hydrocarbon phas es was unreliable, on occasion
reading zero level of the hydrocar bon phase when the phase was, in
fact, present. One evening this lo ss of level on the instrument was
observed as usual but dismissed by the control panel operator
because of the prior history of faulty readings.
A f t e r a n h o u r o f t h i s o p e r a t i o n , the supervisor noted several other
atypical issues in the unit – reduct ion in feed consumption, increase
in waste product, strange separator readings, etc. Since these were
also symptoms of a zero-level condition, he concluded that the loss of
level might be real, and that the unit was actually in an ‘acid runaway’
condition. The fix for such a situation was to stop the feed to the unit
and regroup. However, since neit her the supervisor nor the area
supervisor had authority to shut th e flow, they deferred to the overall
plant night shift supervisor, whose de cision was to wait for four hours
and, if the level was still reading ze ro, then initiate a shutdown. About
six hours after the initial zero level indication, the unit was finally shut
down, but because the shutdown ha d been delayed th e restart took
three days to accomplish vs. about on e hour if it had been initiated
immediately. Because storage for the intermediate feedstock had not
yet been commissioned, about 25,000 ba rrels of LPG had to be flared.
|
INTRODUCTION AND REGULATORY OVERVIEW 13
OSHA, U.S. Occupational Safety and Health Administration, https://www.osha.gov/laws-
regs/regulations/standardnumber/1910/1910.119.
Zerbonia 2001, Robert A. Zerbonia , Cybele M. Brockmann , Paul R. Peterson & Denise
Housley, “Carbon Bed Fires and the Use of Ca rbon Canisters for Air Emissions Control on
Fixed-Roof Tanks”, Journal of the Air & Waste Management Association , 51:12, 1617-1627, DOI:
10.1080/10473289.2001.10464393.
|
138 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
Nature can pose meteorological and geological hazards . (CCPS 2019)
Meteorological hazards are those that naturally occur due to the weather cycle or
climactic cycles, and include flooding, temperature extremes, snow/ice storms,
wildfire, tornado, tropical cyclones, hurricanes, storm surge, wind, lightning,
hailstorms, drought, etc.
Geological hazards are those occurring due to the movements of the earth and the
internal earth forces, and include seismic ev ents, earthquakes, landslides, sinkholes,
tsunami, volcanic eruptions, and dam rupture.
Natural Hazards Triggering Technological Disa sters (Natech) refers to the interaction
between natural disasters and industrial accidents. More information on this area of research
can be found at the UN Economics Commission for Europe. (UNECE) Identifying these natural
hazards and including their potential impact in design and emergency response preparedness
plans is important to prevent their resulting in a process incident. For example, natural hazards
can result in loss of access and power to facilities which can, in turn, result in loss of cooling to
reactive chemical storage. This was evident in the Arkema organic peroxide decomposition
and fire following Hurricane Harvey flooding in 2017. (CSB 2018) Earthquakes can result in
failure of equipment and piping resulting in fires.
Mining operations often create retention basins or dams to hold tailings. In Hungary, the
Kolontar Tailings dam failure released a wave of bauxite into the surrounding area. (AGU)
Tailing dam failures can result in both rapid water current and flooding hazards as well as
longer term toxic exposures. Guidance is availa ble such as the Mining Association of Canada’s
Guide to the Management of Tailings Facilities. (MAC)
Seismic hazards for process fac ilities include both potential toppling of tall structures and
also the resulting escalation of the initial event. In seismic regions a seismic evaluation should
be conducted of tall structures, such as distillati on columns, to determine if actions should be
taken to prevent damage due to a seismic even t. Additional design considerations may need
to be incorporated into facilities located in seismic zones.
Natural hazards can also result in second ary process safety impacts. Consider the
eruption of the Iceland volcano that resulted in a shutdown of air travel in Europe as shown in
Figure 8.5. (NASA) This meant that work to evaluate hazards, analyze risks, and implement
systems to control process safety risks were pu t on hold until travel, and transportation of
supplies, could resume. |
89 5 SELECTING AN APPROPRIATE
PHA REVALIDATION APPROACH
As stated in Chapter 1, the primary goal of a revalidation is to verify that the PHA
document accurately describes the current risk profile of the subject process
unit. While a PHA revalidation can sometimes be accomplished with less effort
and in less time than the initial PHA, this is highly dependent upon the scope and
quality of the prior PHA and thoughtful planning.
The preparation described in Chapters 2 through 4 of this book, and
illustrated in Figure 5-1, were all intended to help the reader answer the
following pivotal question:
Which PHA revalidation approach will be the most resource-
efficient and effective way to produce a complete, compliant,
up-to-date, and thoroughly documented PHA?
Figure 5-1 Revalidation Flowchart – Selecting the Approach |
APPLICATION OF PROCESS SAFETY TO WELLS 67
4.2.3 Shallow Gas
Risks
Shallow gas deposits near to the surface ca n be encountered during drilling before
the BOP and surface casing are in place and can lead to a shallow gas well control
incident. This can be associated with eith er onshore or offshore drilling. Oil is not
normally present with shallow gas. While m ud weight can be increased, if this fails
then it may be necessary to drill a relief well to kill the shallow gas flow.
During a shallow gas incident, it is not normally advised to try to shut in the
well as the surface formation is not strong en ough to provide for containment. A
safer option is achieved using a diverter valv e to direct flow away from the rig floor.
Key Process Safety Measure(s)
Hazard Identification and Risk Analysis : Identification of shallow gas is key to
understanding and managing the risks. Shallow gas is hard to detect, but newer
digitally enhanced seismic analysis can re veal this hazard. Consequences onshore
are primarily related to flammable and potentially toxic gases. Offshore
consequences are similar as shallow gas can bubble to the surface under a floating
drilling rig and create a flammable atmosphere . It can also damage the sea floor and
destabilize a jack-up rig. A shallow gas incident can damage or rupture the drill
string and thus reduce the ability to deliver a heavier mud to the problem zone.
Personnel require evacuation which can be difficult due to the flammable
atmosphere but, as seen in the Snorre A blowout described in the following incident
description, can be done successfully.
Shallow water hazards are similar but without the flammable or sour gas
hazards. They are thus more of an oper ational than process safety problem.
However, depending on the source of the water and if there are nearby receptors,
there can be a pollution risk. For example, if the water source is due to accumulation
of nearby water injection wells, then the water may be contaminated.
4.2.4 High Pressure High Temperature (HPHT) Wells
Risks
Loss of well control risks are heightened when well construction involves high
pressure, high temperature (HPHT) reserv oirs. These have temperatures exceeding
300 ˚F, a pore pressure of at least 0.8 psi/ft, or requiring pressure control equipment
exceeding 10,000 psi. Drilling, comple tions, workovers, interventions and
abandoning wells in HPHT environments ar e at greater risk due to the complexity
associated with the high pressure and high temperature and having a higher
probability of well control incidents and equipment failures. |
74 INVESTIGATING PROCESS SAFETY INCIDENTS
To ensure continuous improvement, an evaluation after each
investigation should include:
• Team thoroughness in the investigation.
• Team effectiveness in applying the techniques.
• Team preparedness in advance of the investigation.
• Equipment performance during the investigation.
• Supply logistics and quality.
To ensure that the management system cont inues to provide the
intended results, periodic reviews and updates are necessary. This action
recognizes that organizations are dy namic, ever-changing, and evolving.
Consider the following critique questions.
Were the investigation techniques applied correctly and fully?
Did the team accurately determine what happened?
Did the team find the management system
failures that led to the in cident (that is, did they
get to root causes)?
Was the team documentation adequate?
Were the right skills available within the team?
What other resources could be used next time?
What should be changed next time?
Is there evidence to suggest that near-misses are being reported?
Have there been any repeat events?
Chapter 14 provides guidance on recommendation implementation
effectiveness, and Chapter 15 details proven methods for enhancing an
incident investigation system.
4.3 M ANAGEM ENT SYSTEM
Implementing a new or upgraded management system normally begins with
training employees, supervision, and management in their respective roles
in the investigation program. Implem entation also includes development
and refinement of the incident da ta management systems. The data
management system should allow users to easily dev elop consistent reports |
204 GUIDELINES FOR MANAGING ABNORMAL SITUATIONS
stability tests that were reviewed in 1988 and 1989 when the process of
batch distillation in 60 Still Base was introduced.
After the modification in 1988, problems started with residue
accumulation in parts of the cont inuous distillation section of the
process. These were stripped and cl eaned out although operators also
noted the accumulation of sludge in 60 Still Base, up to a depth of some
34cm (14 inches).
In June 1992, one of the senior process technologists expressed
frustration about these problems an d the impaired conditions on the
continuous MNT distillation section of the process. A memo was written
stating: “It is my view that we are wi thin five years of a major accident on
the MNT distillation system.”
At some point (date unknown), the steam regulator on the supply to
the heater battery became non-oper ational. This was overcome by
someone opening a bypass valve aro und the regulator until the relief
valve started to lift.
On 10 September 1992, some 11 days before the incident, two of the
40% whizzer oil tanks were fully emptie d to the 60 Still Base, in order to
clean them out for a change of prod uct. Being a vacuum vessel, this
allowed the residual sludge from thes e tanks to be sucked into 60 Still
Base, further increasing the level of solids in the vessel. On Thursday, 17
September, the removal of the slud ge from 60 Still Base was discussed
by a shift manager and area manager. Since this vessel had never been
cleaned out before, they discussed some of the practical measures
required including removal of some st eps and provision of a skip (steel
dumpster) to collect the sludge.
A batch distillation of the material in the 60 Still Base then took place
on Saturday 19 September in prepar ation for the work to start the
cleanout of 60 Still Base the fo llowing Monday, 21 September 1992.
7.3.4.2 Organization
In parallel with the process changes, several organizational changes took
place at the Castleford site. The original management structure was a
traditional, hierarchical one, wher e plant managers managed individual
plants and each shift comprised a shift supervisor and a small number
of shift operators. |
163
Some batch reactions have the po tential for generating very high
energy levels. If all of the reactant s (and catalysts, if applicable) are
charged into a reactor before the reac tion is initiated, and two or more
of the materials in the reactor reac t exothermically, a runaway reaction
may result. The use of continuous or “semi-batch” reactors to limit the
energy present and to reduce the risk of a runaway reaction should be
considered. The term “semi-batch” refers to a system where one
reactant and, if necessary, a cataly st is initially charged to a batch
reactor. A second reactant is subs equently fed to the reactor under
conditions such that an upset in the reacting conditions can be detected
and the flow of the second reactant stopped, thus limiting the total
amount of potential energy generated in the reactor.
Additional discussion regarding reac tor design strategies is covered
in Section 3.2 on Minimization (as an inherently safer design strategy),
and in Section 8.4 on the process design.
Distillation . There are options to minimize hazards when distilling
materials that may be thermally unstable or have a tendency to react
with other chemicals presen t. These options include:
Trays without outlet weirs
Sieve trays
Wiped film evaporators
An internal baffle in the base section to minimize hold-up
Reduced base diameter (Ref 8.52 Kletz 1991)
Vacuum distillation to lower temperatures
Smaller reflux accumulators an d reboilers (Ref 8.30 Dale)
Internal reflux condensers and reboilers (Ref 8.30 Dale)
Column internals that minimize holdup without sacrificing
operational efficiency (Ref 8.30 Dale)
Another option is to remove toxic, corrosive or otherwise hazardous
materials early in a distillation sequ ence, reducing the spread of such
materials throughout a process (Ref 8.82 Wells).
Low-inventory distillation equipment, such as the thin film
evaporator, is also available and shou ld be considered for the distillation
of hazardous materials. This equipme nt offers the additional advantage |
ACRONYMS AND ABBREVIATIONS xxvii
MCC Motor Control Center
MIE Minimum Ignition Energy
MOC Management of Change
MOC Minimum Oxygen Concentration
MOOC Management of Organizational Change
NASA National Aeronautics and Space Administration
NDT Nondestructive Testing
NFPA National Fire Protection Association
OD Operational Discipline
OIMS Operational Integrity Management System (ExxonMobil)
OSHA U.S. Occupational Safety and Health Administration
PAC Protective Action Criteria
PFD Process Flow Diagram
PFD Probability of Failure on Demand
PHA Process Hazard Analysis
P&ID Piping and Instrumentation Diagram
PLC Programmable Logic Controller
PRA Probabilistic Risk Assessment
PRD Pressure Relief Device
PRV Pressure Relief Valve
PSE Process Safety Event
PSI Process Safety Information
PSI Process Safety Incident
PSM Process Safety Management
PSO Process Safety Officer
PSSR Pre-Startup Safety Review
QRA Quantitative Risk Analysis
RAGAGEP Recognized and Generally Accepted Good Engineering Practice
RBPS Risk Based Process Safety
RMP Risk Management Plan |
39
potentially affected population. A technology may be inherently safer
than another with respect to some ha zards but inherently less safe with
respect to others and may not be safe enough to meet societal
expectations. IST options can be location and release scenario
dependent, and different potentia lly exposed populations may not
agree on the relative inherent safety characteristics of the same set of
options.
ISTs are based on an informed deci sion process: Because an option
may be inherently safer with respec t to some hazards and inherently
less safe compared to ot hers, decisions about the optimum strategy for
managing risks from all hazards are re quired. The decision process must
consider the entire life cycle, the fu ll spectrum of hazards and risks, and
the potential for transfer of risk from one impacted population to
another. Technical and economic feas ibility of options must also be
considered. Risk reduction criteria w ill be determined by the nature of
the hazards or threats and will requir e consideration of conflicts among
multiple hazards and threats.
Inherently safer options should also be considered for the entire
supply chain, including manufacturing, use, storage, transportation, and
disposal. Tradeoffs are involved in terms of moving risk from one
location in the supply chain to another (Ref 2.6 Berger, Ref 2.2 ACS). For example, reducing onsite inventor y of a hazardous raw material may
require more frequent shipments and subsequent risk along the
transportation route, or increased inventory at the supplier location.
Marshall (Ref 2.23 Marshall 1990, Ref 2.24 Marshall 1992) discusses
accident prevention, control of occu pational disease, and environmental
protection in terms of strategic and tactical approaches. Strategic
approaches have broad significance and represent “once and for all” decisions. The inherent and passive categories of risk management would usually be classified as strate gic approaches. In general, strategic
approaches are best implemented at an early stage in the process or
plant design. Tactical approaches, wh ich include active and procedural
risk management categories, tend to be implemented much later in the
plant design process, or even after the plant is operating, and often involve much repetition, increasing co sts, as well as the potential for
failure. However, it is never too late to consider inherently safer alternatives. Major enhancements to inherent safety have also been |
8.1 Flixborough, North Lincolnshire, UK, 1974 | 107
Flixborough taught us the importance of formally, thoroughly, and
consistently managing process changes, including changes that are
considered temporary or emergency. The engineers at Flixborough did
evaluate the changes to reactor train throughput that would be required to
operate with one less reactor. However, they did not evaluate whether the
planned temporary bypass piping had been properly designed to support its
weight, handle the vibrations resulting from two angle bends, and endure the
expected thermal stresses (Figure 8.1). After two months of exposure to stress,
vibration, and fatigue, the piping failed, releasing a large cloud of flammable
vapors that ignited and exploded.
Figure 8.1 Temporary Bypass on Flixborough Reactor 5 (Source: UKDOE 1975)
Most of us stop our consideration of
Flixborough there. But we can learn a lot more
from this incident. The jacket of reactor 5 also
failed due to a stress corrosion crack and thermal
stress. The corrosion resulted from a temporary
change to spray process water on the reactor
head. Nitrates were added to boost heat transfer
capacity. The nitrates eventually led to stress
corrosion cracking of the jacket, however
(Figure 8.2). Today, as then, incidents happen
when companies apply temporary fixes rather
than having the operational discipline to shut
Figure 8.2 Stress
Corrosion Crack on
Flixborough Reactor 5
(Source: UKDOE 1975) |
2 INVESTIGATING PROCESS SAFETY INCIDENTS
The first edition provided a timely treatment of incident investigation
including:
• a detailed examination of the role of incident investigation in a
process safety management system,
• guidance on implementing an incident investigation system, and
• in-depth information on conducting incident investigations, including
the tools and techniques mo st useful in understanding the underlying
causes.
The second edition, released in 2003, built on the first text’s solid
foundation. The goal was to retain the know ledge base provided in the
original book while simultaneously updating and expanding upon it to reflect
the latest thinking. That edition pres ented techniques used by the world’s
leading practitioners in the science of process safety incident investigation.
This third edition is a further enhancement of the second edition.
Specific emphasis has been placed on updating investigation techniques and
analytical methodologies, and applying them to example case studies where
possible. Expanded topics include scientific va lidation of hypotheses,
rigorous physical evidence documentation and examination, scientific
analysis, hypothesis rejection and substantiation, learnings from repeat incidents, and means to institutionalize learnings within an organization.
1.2 INVESTIGATION BASICS
Successful investigations are dependent on prep lanning, documented
procedures, appropriate investigator training and experience, appropriate
support from leadership, and necessary resources (personnel, time, and
materials), to conduct a thorough investigation. It is imperative that operating organizations conduct careful and comprehensive investigations
that are factual and defensible. Develo ping and following written procedures
allows organizations to consistently respond
promptly and effectively,
establishes the basis for continuous improvement, and helps preserve a
company’s “license to operate”.
1.2.1 The First Step in conducting a successful incident
investigation is to recognize when an incident has occurred so that an
Incident Management System (Chapter 4) can be activated. Linked with
incident recognition are Initial Notification, Classification, and Investigation
(Chapter 5). |
160 GUIDELINES FOR MANAGING ABNORMAL SITUATIONS
Example Incident 6.1 – Fire Protection System Found Disabled
During a field review of safety sy stems in one unit, the auditor noted
that the pumps were provided wi th a sprinkler system that was
intended to provide a rapid response to a local fire. Curious as to the
source of this water, the auditor followed the supply piping back to a
manifold. This manifold had several va lved lines tying into it, so that it
was not immediately clear which va lve would lead to which user.
Furthermore, a painter had left a thic k layer of paint on all the valves,
so that a significant effort would be needed to operate the valves in
an emergency. Beyond that, the au ditor traced the source of the
manifold’s water to yet another manifold, where those valves were
blocked in. The condition and position of the two sets of valves were
in themselves not an emergency si tuation; however, they were
important to the function of a mi tigation system to address an
emergency. In the event of an ac tual fire, the response would have
been delayed and ineffective.
Lessons learned in relation to abnormal situation management:
Understanding abnormal situations: A lack of knowledge about
the positioning of the block valves, their readiness, and
functionality. The valving was abnormal, yet the consequences
were not considered.
Process Monitoring: Continually mo nitor the readiness of safety
systems or include confirmation that a required periodic
checklist has been performed.
Car Seal Management: The utilization of a car seal open and car
seal closed system to ensure valves are maintained in their
preferred position is a positive way to minimize valving errors.
|
EQUIPMENT FAILURE 205
Figure 11.20. Horizontal peeler centrifuge with clean-in-place system and discharge chute
(Patnaik)
Figure 11.21. Cross sectional view of a continuous pusher centrifuge
(Patnaik)
|
DEVELOPING EFFECTIVE RECOM M ENDATIONS 285
The incident investigation team should consider including
recommendations that examine inhere ntly safer design. Changes can be
either beneficial or detrimental, so investigators should be alert for features
in recommendations that are inherently less safe. Two common examples of
design changes that can increase overall risk are the use of flexible joints and
the use of glass (rotameters, bulls eyes, sight gl asses, or additional control
room windows) (Englund, 1991). Seal-less pumps are generally considered to
be inherently safer than pumps with mechanical se als. The failure mode(s) of
any recommended new equipment should be carefully considered before a
decision is made to implement the change.
12.3.2 Layers of Protection
The concept of multiple layers of protection (barriers) has widespread
support throughout the refining and chemical processing industry. By
providing sufficient layers of protection against an accident scenario, the
potential risk associated with that accident can be avoided or at least
reduced. For a given scenario, only one barrier must work successfully for
the consequence to be prevented. However, since no single barrier is
perfectly reliable, multiple layers of protection are often provided to render
the risk of the incident tole rable. It should be under stood that these multiple
layers of protection are fully indepen dent; otherwise, there could be fewer
barriers than expected. This is illust rated in Chapter 2, where the “Swiss
Cheese Model” is discussed.
The failure of one or more barriers mi ght be identified as part of an
incident investigation. Recommendations arising from an individual barrier
failure can be made at various levels . Trevor Kletz said that accident
investigation was like peeling an onion: “The outer layers deal with the immediate technical causes while the inner layers are concerned with ways
of avoiding the hazards and with the und erlying causes, such as weakness in
the management system.” He identified three layers
of recommendations, as
follows: (Kletz, 1988)
• First layer remedies use immediate technical recommendations
targeted to prevent a particular incident. Consider the case where
an employee is injured by inhalation exposure while taking a liquid
chlorine process sample. Firs t-layer recommendations would
address such items as changes to the sampling procedure, refresher
training, and selection and use of personal protective respiratory
equipment.
• Second layer recommendations focus on avoiding the hazard. A
deeper and broader perspective is used for this second layer, and |
238 INVESTIGATING PROCESS SAFETY INCIDENTS
Figure 10.21 Exit Piping Crack Branch
What if the team was not able to obtain any physical evidence? They
could use the absence of any corrosion inspection records plus knowledge
of the expected corrosion (i nternal and external) of the system as an indicator
of whether corrosion was a credible possibility.
With no evidence at all, the team might develop each hypothesis as a
separate branch of the tree and try to address potential causes of corrosion,
improper choice of materials, flange failure, or other items.
After collecting and analyzing the available evidence, the incident
investigation team constructed the logic tree diagrams shown in Appendix D. These diagrams present, in a logical and systematic format, the
sequence
of events and conditions that ultimately resulted in the major incident. The
simplified qualitative fault-tree indicates various events and conditions that
|
Appendix B - Major accident case studies 385
B.2 Bayer Crop Science plant explosion in West Virginia, U.S.
In 2008, a large explosion led to fatality of two workers at the Bayer Crop Science
plant in West Virginia, USA [26]. The fire burned for more than four hours. Two
contractors and six firefighters were trea ted for possible toxic exposure [83]. The
damaged plant is shown in Figure B-2.
‘What happened’ is summarized after Figure B-2.
A thermal runaway reaction (a chemical reaction) occurred inside a 4,500 gallon
(17,000 liter) pressurized residue treater, ca using it to fracture. Highly flammable
solvent sprayed from the vessel and ignited, causing fire.
Figure B-2 Bayer Crop Science plant damage
(reproduced from www.csb.gov)
The incident happened during the first methomyl restart after an extended
outage to install a new process control system and a stainless-steel pressure
vessel. The steps leading to this accident are outlined next:
• A methomyl unit was due to be restarted after replacing the control
system and the residue treater vessel.
• Prior to start-up, the vessel should have been loaded with solvent and
the solvent preheated. Neither of these actions were done.
• At 04:00 the outside operator manually opened a feed valve to start
filling the residue treater vessel with methomyl. The methomyl should
have been instantly mixed with the missing solvent.
• With a low flow rate, more than 24 hours is required to fill the residue
treater to the normal operating level (50%). During this time the mix was
|
PHA Revalidation Requirements 27
would be aware of every possible RAGAGEP. Hence, as mentioned in Chapter 1,
organizations (e.g., companies, trade associations, and professional societies)
often develop checklists to remind people of key points to verify during original
designs, PHAs, and revalidations. An excellent example of this is Bulletin 109,
published by the International Institute of Ammonia Refrigeration for the mutual
benefit of its membership [28]. It comp iles safety criteria for a variety of
equipment (e.g., compressors, condense rs, evaporators, and piping) normally
used in refrigeration systems. The foll owing paragraphs briefly describe some
common RAGAGEPs that PHA reva lidation teams might consider:
International Electrotechnical Commission (IEC) 61508, “Standard for
Functional Safety of Electrical/Elect ronic/Programmable Electronic Safety-
Related Systems” [29]. This standard co vers safety-related systems, which may
include anything from simple actuated valves, relays, and switches up to
complex programmable logic controllers. The standard specifically addresses
safety instrumented systems and how their failure to execute their safety
functions either on demand or conti nuously can result in safety-related
consequences. The overall program to en sure system reliability is defined as
“functional safety.” IEC 61511 is the proc ess industry derivative of IEC 61508. Risk
judgments in a PHA of an automated process may involve supplemental risk
assessments (e.g., LOPA) that are cont ingent upon the reliability of safety
systems covered by this standard; in these cases, it is essential to have a
revalidation team member(s) familiar with its guidance.
American National Standards Institute/National Fire Protection Associ-
ation (ANSI/NFPA) 70, “National Electric Code” [30]. As its title indicates, this
code applies to a wide range of electr ical power systems and their components.
Various chapters address everything fr om basic definitions and rules for
installations (e.g., voltages, connections , markings, and circuit protection) to
general-purpose equipment (e.g., conducto rs, cables, receptacles, and switches)
to special equipment and conditions (e.g ., signs, alarms, emergency systems,
and communications). Articles 500 to 506 are of particular interest to
revalidation teams trying to ensure th at process changes have not created or
altered areas with potentially explosiv e concentrations of dusts or vapors.
European Directive 94/9/EC, commonly referred to as the Atmospheres
Explosible (ATEX) Directive, similarl y addresses equipment in potentially
explosive atmospheres.
NFPA 652, “Standard on the Fundamentals of Combustible Dust” [15]. Dust fires
and explosions have resulted in fatalit ies and extensive property damage. Yet
the materials involved may be as seemin gly innocuous as sugar or polyethylene,
so they are not classified as highly hazardous materials. Dust hazard analyses |
Appendices 193
Q T R
XII. Electrical Classification
Is there an electrical classification document?
Does the electrical classification appear correct and complete?
Has the electrical classification do cument been recently revised?
Have significant changes made si nce the system was originally
constructed (addition of new mate rials, new sources of flammable
gases or vapors, new low points [e.g., sumps or trenches] at grade)
been included in the electrical classification document?
Are the design and maintenance of ventilation systems adequate?
Are there safeguards to alert operators when a ventilation system
fails?
Are ventilation systems being properly maintained, and are alarms
and interlocks on these systems periodically function checked?
Is adequate maintenance being do ne to function check natural
ventilation systems?
Are there technical bases for design changes to the ventilation
systems?
Are ventilation systems verified to be adequate for new gas or vapor
loads?
Are there adequate controls to ensu re that electrically classified
equipment is replaced with equipment of equal or higher
classification?
Are boundaries between electrically classified areas physical
boundaries?
Are Division 1 areas necessary (if there are any)?
Are there adequate controls (e.g., a hot work permit system) on
repair and construction activities , including work by contractor
personnel?
Are there specific requirements for pe rsonnel in classified areas (e.g.,
static dissipative attire, prohibition of ignition sources such as cell
phones)?
Does the electrical classification adequately reflect the effects of
different modes of operation (e.g., normal operation, maintenance,
startup, infrequent operating modes such as reactor regeneration or
operation with a portion of the system bypassed)?
XIII. Contingency Planning
What expansion or modification pl ans are there for the facility?
Can the unit be built and maintained without lifting heavy items over
operating equipment and piping? |
Pipes
97
pipe around the trimmer unit. This bypass pipe can be
used during the start‐up of the plant when there is no real need to bring all the units in operation at once, and the trimmer unit can be bypassed (Figure 6.73).
6.12.4
Piping f
or Units in Parallel
Units can be placed in parallel, and their piping is a bit
tricky. Here we want to focus on the pipe sizes in such arrangement.
It is obvious that if there are two similar equipment in
parallel and one of them is the operating piece of equip-ment and the other, a spare one (it means 2
× 100%
s
paring philosophy), the pipe size does not change after
splitting. This concept is shown in Figure 6.74.
But if both pumps are operating (it means 2 × 50%
spar
ing philosophy), the flow splitting on the inlet side of
the pipes in a way that each pump will receive half of the flow. Here the rule of thumb says that the size of each branch is
2 of the size of main header, as shown in
Figure 6.75. Based on this, when a pipe flow is branched to three even flows, the size of each branch would be
3
of the size of main header.
6.12.5 Piping f
or Pressure Equalization
The pipe for pressure transfer or pressure equalization
can be much smaller than the main pipe size (i.e. two or three size smaller).
The pipe for pressure equalization can be connected to
two sides of blocking valves for ease of opening or between two tanks to allow initiating the liquid flow between them.6.13 Pipe Size Rule of Thumbs
It is not easy to tell from a P&ID whether the pipe size is correct. However, when two or more pipes are con-nected to each other, it is easier to check the accuracy of pipe sizing.
Below are some cases through which the pipe size can
be checked:
1)
When two (or mor
e) pipes are merging together, the
resultant pipe may have a larger size. Here the word
may is used because there are some cases that this
rule is not valid. For example, when a 2″ pipe is merged to a 20″ pipe, the size of pipe after connection of the 2″ pipe is less likely to be changed to a larger size, like 22″.
2)
When a pipe i
s split into two or more branches, the
size of branches may be smaller than the main pipe.
6.14 Pipe Appurtenances
Pipe appurtenances are mainly classified into three main groups of valves: fittings, process items, and non-process items.
Valves are piping components that actively affect
flows. Active means they should have a movable part.
A gate valve has a moving stem. A check valve has a moving flap.
Fittings are piping appurtenances that passively affect
flows. Examples of fittings are elbows and reducers.
Process items are piping appurtenances that are
installed on piping and change some process feature of the flow. Examples are strainers and silencers. Process items generally tagged in P&IDs as SP item.Recirculation pump(b)
(a)Unit
Unit
Figure 6.72 (a, b) Unit r ecirculation pipe.
Unit 1 Unit 2
Figure 6.73 Ser ies units pipes.Unit 1X/uni2033
X/uni2033
X/uni2033Unit 22×100%
Figure 6.74 Pipe siz es of parallel units, a spare one operating.
Unit 1X/uni2033.(2)0.5
X/uni2033.(2)0.5X/uni2033
Unit 22×50%
Figure 6.75 Pipe siz es of parallel units, both operating. |
131 10
REAL MODEL SCENARIO: LEAKING HOSES AND
UNEXPECTED IMPACTS OF CHANGE
“A [person] who carries a cat by the tail learns something [they] can learn
in no other way.”—Mark Twain, Author and Humorist
Feijoada Pharma produces a range of generic drugs
in a modern facility outside São Paulo, Brazil. Each
of its five primary reactor trains run one- to three-
month campaigns to produce active
pharmaceutical intermediates. The reactors are
then reconfigured for the next product.
Each reactor can be fed via multiple routes, including:
• dip pipe
• free-fall from a nozzle in the reactor head
• free fall via one or more spray balls in the reactor head
• through a recirculation line.
These feed routes are accessed through four hose connections near the
reactor that are grouped close together for convenience but are clearly
labeled. The materials to be fed are similarly piped close to the reactor,
terminating in hose connections. These, too, are grouped close together for
convenience and clearly labeled.
Operators connect the desired feed material to the desired feed port
using the appropriate flexible hose designated in the operating procedure.
Raw materials can also be fed to the reactor through any of the ports from
drums. Some hoses are kept connected for the duration of the campaign,
while others are purged and disconnected to allow a different raw material to
be fed via a given feed route. The individuals and
company in this
chapter are
completely fictional. Driving Continuous Process Safety Improvement From Investigated Incidents By CCPS and EI
© 2021 the American Institute of Chemical Engineers |
72 INVESTIGATING PROCESS SAFETY INCIDENTS
apply lessons learned from an incident, no t only at a facility level, but also
across the organization.
Employees are affected by the recommendations. Their responsibilities
include:
Using new or modified equipment properly.
Abiding by procedural improvements.
Giving feedback to management wh en something is not working as
expected.
Sharing their knowledge when they find a better or safer way to
address the problems identi fied in the investigation
In summary, developing the recommendations is a responsibility of the
incident investigation team. Accepting and implementing the
recommendations is a management responsibility. The inclusion of the
elements of the recommendation in dail y work practice is the responsibility
of each individual affected by the recommended action.
4.2.11 Implementing the Recommendations and Follow-up Activities
Resolving recommendations and followi ng up on their effectiveness is a
cornerstone of all manage ment systems. Once a recommendation has been
accepted for implementation, a clear, auditable document trail should be
established and maintained. The recommendations should not only be implemented but also, they need to be su stained. For lastin g results, it is
wise to audit implemented recommendat ions periodically to ensure that
they are continuing to achieve the
intended objectives.
It is the prevailing opinion of many regulatory agencies that any
changes in the originally accepted recommendation should be thoroughly
documented. If a recommendation is modified in scope or time commitment, or is otherwise not implem ented as originally planned, then
the
basis for this decision should also be documented. The concept of an
auditable trail is mentioned in regu latory and legal activities. If a
recommendation is rejected or modified, the basis for the rejection or change
should be thoroughly documented after review with the investigation team.
These requirements should be reflected in the incident investigation
management system and sh ould be emphasized wh en personnel at all
levels are trained.
The management system sh ould indicate the importance (priority) of the
recommendation, assignment of responsibility, and method for verifying and |
EQUIPMENT FAILURE 199
A B
Figure 11.16.A. Example distillation column schematic
(Bouck)
Figure 11.16.B. Typical industrial distillation column
(©Sulzer Chemtech Ltd.)
Figure 11.17. Schematic of carbon bed adsorber system
(OSHA a)
|
206 | 6 Where do you Start?
broadly, so that all sites and units feel equally included in the
process and change happens more quickly.
Culture surveys should be perform ed anonym ously, and
ideally by an independent party. At the outset of culture
improvement efforts, m utual trust m ay not yet have been
developed, so respondents m ay hesitate to give full open and
frank input to assessors who represent com pany management. It
m ay not be necessary to use an independent party for re-surveys
of organizations where m utual trust is already high, but is still a
good idea just in case there has been some slippage in the culture.
Whoever conducts the surveys, anonymity should be preserved
both in collecting and in reporting the data. When sub-segmenting
the data, the number of people in a sub-segm ent should be large
enough to prevent identifying individual respondents.
While culture surveys typically produce narrative data, it is
important for statistical analysis purposes to develop clear
definitions m apping narrative input to num erical scores. This will
likely require identifying a range of potential responses to every
question, and decide how each would fit on the scale of potential
responses, perhaps from 0% to 100%.
In culture surveys, it is not unusual for some employees to
respond very negatively to questions they do not really feel
negative about. They may do this thinking they are punishing
m anagement, or m ay wish to emphasize a negative response to
other somewhat related questions. In some cases, the fear of
m anagement reprisals m ay lead one member of the group to
answer negatively on behalf of the rest, to deliver the message
while saving their peers.
Therefore, a m eans of interpreting extreme input is also
needed. This may involve observing the work group with the
apparently outlying feedback or asking members of the group
why som e of their peers reacted as they did. Follow-up interviews
m ay also be warranted. Of course, the negative input m ay also be |
B.2 INHERENT SAFETY ANALYSIS - INDEPENDENT PROCESS HAZARD
ANALYSIS (PHA)
Table B.5 is an example of an IS Anal ysis approach, which is similar to a
typical PHA, but focuses exclusively on inherent safety.
The analyst considers a hazard, such as runaway reaction caused by
water reactivity in a reactor and sets a safety objective, such as “minimize
potential for runaway reaction in the feed to the reacto r.” The team then
documents each potential cause of th e hazard being evaluated, reviews
the consequences, existing safe guards, and potential means of
eliminating it or reducing its risk through ISD strategies.
Considering the four ISD strategies, the team documents potential
recommendations that may address the concern using the order of First Order ISD, Second Order ISD, follo wed by Layers of Protection. Each
strategy is considered. Ideas that are feasible, practical, and best address
the hazard are generated. The approach acknowledges that other risk management strategies besides ISD may be more effective.
464 |
348 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
The mechanical design and control of proce ss equipment should maintain the process at
the operating temperature and pressure. Alarms are typically provided to alert operators when
a temperature, pressure, or level operating limit is being reached. The operators can then take
action to bring the process back to normal op erating conditions. If the level continues to
exceed limits, then an instrumented system ma y be provided to take action (e.g. shut/open
valves) to prevent an unsafe condition being reached. These concepts were discussed in
Section 10.5.
A pressure relief valve is an active mitigation device that is often referred to as the last
line of defense as it is intended to protect equipment should all other systems fail. If an
overpressure occurs in a vessel and associated piping, pressure relief valves are designed to
open at a predetermined pressure to allow the pressure to be relieved before the equipment
fails. The three common types of relief valves are conventional, balanced bellows, and pilot
operated. They have different operating charac teristics that make them appropriate for
different operating conditions. Common to all is that they are designed to operate at a
specified set pressure that is related to the MA WP and operating limits (refer to section 10.6).
In some processes, pressure relief valves disc harge to a flare system where the diverted gas
and fluid are safely burnt. API STD 520 Sizing, Se lection and Installation of Pressure-relieving
Devices and API STD 521 Pressure-relieving and Depressuring Systems provide guidance on
these topics. (API STD 520 and API STD 521)
If a loss of containment occurs such as a tank overfilling, a containment dike (passive) can
be provided to contain the fluid and avoid its flowing in areas containing ignition sources or
environmentally sensitive areas. If a loss of cont ainment and fire occurs in a process unit, an
automatic suppression system (active) may be acti vated to control the fire and sloped drainage
provided to limit the extent of the fire.
Occupied buildings may be protected by blas t or fire walls (passive) to mitigate the
potential impacts on building occupants. |
Conducting PHA Revalidation Meetings 151
7.4 PRINCIPLES FOR SUCCESSFUL REVALIDATION
MEETINGS
Actual experience in conducting revalid ations, by PHA practitioners across a
number of companies, has highlighted so me keys for success, as well as some
things that can impede success. While none of the items listed are absolute rules,
they do provide valuable guidance.
Successful Practices:
• Having a formal code of conduct or team charter that fosters
participation by all team members
• Ensuring the team includes members with all the required skills and
diverse experience
• Including process experts who will be available as needed for the
revalidation sessions and include them in the opening meeting
• Informing the team members of the revalidation strategy for each
aspect of the PHA (core, complementary, and supplemental
analyses) and explaining the rationale for each
• Refreshing the team members’ understanding of the organization’s
risk tolerance criteria
• Ensuring that some team members were not involved in
performing the prior PHA
• Preparing appropriate worksheets to capture revalidation team
discussions
• Providing team members with an overview of process operations,
an overview of the physical layout , and a refresher in the analysis
techniques, as necessary
• Providing team members with an overview of changes since the
prior PHA
• Suspending a team session when an adequate team is not present
and rescheduling a later time when required participants (or
substitutes with similar qualifications) will be available
• Providing team members with an overview of recent, relevant,
process safety incidents
• Performing a detailed review when Updating the prior PHA. A
detailed review affords the PHA revalidation team the time and
resources to help identify new concerns/hazards that may have
been overlooked in the prior PHA |
18
Inherently safer concepts will enhance overall risk management
programs, whether directed towa rd reducing the frequency or
consequences of potential incidents.
2.4 INHERENTLY SAFER STRATEGIES
Approaches to achieving inherently safer processes and plants have
been grouped into four major inhere nt safety strategies. The names or
titles of these strategies were estab lished in the 1st and 2nd editions of
this book. These groupings follow the original treatment of the topic of
inherent safety as published by IChemE and IPSG (Ref 2.17 IChemE) and
Kletz (Ref 2.20 Kletz 1984, Ref 2.19 Kl etz 1991). However, in this earlier,
seminal work, different names/titles we re used. In general, these may be
considered subsets of the four core strategies. These different
names/titles and how some strategies have been incorporated into the
four used herein are presented in this section for clarity and as a reference in interpreting older work on inherent safety:
Minimize Using or having smaller quantities of hazardous
substances (also calle d intensification).
Substitute Replace a chemical/material with a benign or less hazardous substance; or repl ace a process or processing
technology with one that is benign or is less hazardous.
Moderate Use less hazardous or energetic processing or
storage conditions, a less hazardous form of a material, or facilities that minimize the impa ct of a release of hazardous
material or energy (also called Attenuation and Limitation of
Effects ).
Simplify Design facilities which eliminate unnecessary complexity and make operating erro rs less likely, and which are
forgiving of errors that are made (also called Error Tolerance).
These inherently safer design strategies are discussed in more detail
in Chapters 3-6. Examples can be found in Chapter 8, which discusses inherently safer solution opportunities throughout the life cycle of a process.
Table 2.1 presents a mapping of th e original concepts to the CCPS
ISD strategies as restated by Kletz in 1998, as well as others who have |
Heat Transfer Units
209
valves on the bottom heat exchanger. Generally there is
not enough room to place drain or vent valves between the stacked heat exchangers. Even chemical cleaning can be reduced in this arrangement.
As there is generally not enough room between the
two stacked heat exchangers, the sensors can be deleted and only the “location” for the portable sensors are left. The concept of location for portable sensors will be cov-ered in Chapter 13.
11.8.2
Heat Ex
changers in Parallel
Heat exchangers can be placed in parallel when all of
them are operating, or in some less common cases to provide spare capacity for the heat exchanger.
If the flow rate to a heat exchanger is huge, and/or the
required temperature change is high, a heat exchanger with an overly high heat transfer area may be needed. Each type of heat exchanger has a limitation on the heat transfer area. Therefore, sometimes splitting the flow rate and putting two or more heat exchangers in parallel may be needed to avoid placing a heat exchanger that needs an overly high heat transfer area. The limitation on the heat transfer area for each heat exchanger is
dict
ated by technical and economical factors but some-
times can be deviated from. For example very large heat exchangers with very large heat transfer areas will require bringing a heavy duty crane to the plant when the heat exchangers need to be sent to the workshop for maintenance. Large cranes are not available in all plants and usually only large plants can afford to keep them. Therefore, we can have multiple heat exchangers in par -
allel and all of them are working, for example, 2
× 50%
a
pplications.
The other case where we may have parallel heat exchang-
ers is when we need a spare heat exchanger. Generally speaking, heat exchangers are too expensive to allow us to keep them as a spare in plants. Therefore it is very rare to see a parallel heat exchanger 2
× 100%, which me
ans one
operating heat exchanger and another spare heat exchanger. However, in some cases, for example if the service fluid is very fouling, we may have a spare heat exchanger.11.9 Aerial Coolers
If it is decided to use ambient air as the cooling medium on the shell side of a S&T HX, the type of heat exchanger can be used is an “aerial cooler. ”
In aerial coolers, a bundle of tubes (generally finned
tubes) is secured in a frame and there is no shell at all. Air blows through the tube bundle with the help of fan(s). Aerial coolers have the advantage that they have no need for a cooling medium because they use ambient air for cooling purposes. However, they need electricity for the operation of the motor that is connected to the fan.
Aerial coolers are generally used in multiple units in
plants.
The smallest component of an aerial cooler is the “tube
bundle. ” Each tube bundle has one set of dedicated head-ers, inlet header and outlet header. Each tube bundle may have one or two (even up to four) inlet process flows and the same number of outlet process flows (Figure 11.9).
A “unit” is several side‐by‐side tube bundles that work
as a single piece of equipment and carry one tag on the P&ID.
Aerial coolers can be seen in process plants as “banks” ,
which are large pieces of equipment. Each bank of aerial coolers can be more than one tagged aerial cooler in a P&ID. One (or more) specific area of a plant may be ded-icated to aerial coolers and all the aerial coolers of the plant will be located there as a “bank” (Figure 11.10).
No gauges in between
DrainVent
TW
PPTW
PP
Figure 11.8 Stacked hea t exchangers.
Figure 11.9 The tube bundle of an aer ial cooler.
An aerial cooler bank
A unit
A unit
Figure 11.10 The unit and bank in aer ial coolers. |
Piping and Instrumentation Diagram Development
400
However if non‐coincident “design pressure @ design
temperature” is selected one check should be done to
make sure nothing is missed.
This check is: “the pressure that an item can tolerate
at the highest absolute temperature should be checked too. ” This check basically means making sure that the pressure corresponding to the non‐coincident design temperature is not higher than the selected design pressure.
The design temperature of an item could be decided
based on a specific margin on the HHT (high‐high temperature) of the item. The margin could be any number from 5 to 30 °C and is instructed by the company guidelines.
18.8.2
Sour
ces of Rebel Pressures
Design pressure is decided based on rebel pressure.
However there are some cases that rebel pressure can-not be used for the purpose of design pressure specifica-tion. These are the cases where there is no specific maximum sustainable rebel pressure. For example if the discharge side of a positive displacement valve is closed off, the pressure will rebel and increase. However as this pressure doesn’t eventually stay at a specific value, it cannot be used as the design pressure. Such cases can only be handled by placing a pressure safety device, as stated in Chapter 12.
In Table 18.11 some reasons for rebelling pressures,
either on the high pressure side or low pressure side, are listed.
Here we explain one important rebel high pressure and
one rebel low pressure scenario.
The rebel high pressure can be decided to be the “dead
head pressure or shut‐off pressure. ” It is very common to see the “design pressure” of items on the discharge side of a dynamic fluid mover if it is decided based on the “dead head differential pressure” of the fluid mover.The rebel low pressure can be decided to be “full vac -
uum” for the equipment that may need “steaming out” during its life cycle in the plant. If a piece of equipment deals with oily material it may need steaming out for cleaning purposes. It has been observed before that a ves -
sel was cleaned by steaming‐out, and a quick but harsh rain caused quick condensation in the vessel, which led to a vacuum inside of the vessel and the vessel crumpled like a piece of paper. For such cases the design vacuum of the vessel should be specified as “full vacuum. ”
18.8.3
Sour
ces of Rebel Temperatures
Listing the scenarios for rebel temperatures are easier
where there is something that change the temperature of the process fluid.
For example in an exothermic reactor, the HHT could
be decided based on the maximum temperature attained when the cooling water to the reactor jacket is – for whatever reason – stopped.
The other example is the HHT for a piece of equipment
downstream of two heat exchanger in series may be decided when one heat exchanger (possible the one with larger duty) fails to do its functionality.
However there are some other cases that rebel tem-
peratures exists because of other reasons.
In Table 18.12, some reasons for rebelling temperatures,
either on the high temperature side or low temperature side, are listed.
18.8.4
Design P
ressure and Design
Temperature of Single Process Elements
Below the design pressures of several items are discussed.
●Tank: the tank design pressures are requested by pro-
cess engineers and are provided by the mechanical engineers of the fabricator. The requested design pressures, however, should be less than the maximum allowable design pressure dictated by the associated
Table 18.11 Specific rebel pr essure scenarios.
Rebel high pressure Rebel low pressure
●Centrifugal fluid mover
discharge closing off: dead head pressure
●Fail open of control valve or regulator where it is connected to high pressure reservoir
●Runaway reaction where the products of side‐reactions are gaseous
●Vaporization (because of abnormal heat) ●Fail open of control valve or regulator where it is connected to vacuum reservoir
●Runaway reaction where the product of side‐reactions are liquid while the raw material are gaseous
●Vapor condensation (because of abnormal cooling)Table 18.12
Specific rebel t
emperature scenarios.
Rebel high temperature Rebel low temperature
●Runaway exothermic reaction
●Fail open of control valve or regulator where it is connected to high temperature fluid ●Runaway endothermic reaction
●Fail open of control valve or regulator where it is connected to high temperature fluid
●Quick vaporization (because of pressure drop)
●Quick pressure drop of a liquefied gas because of Joule–Thomson effect (in some cases temperature increases) |
251
HAZOP WORKSHEET
Area:
Unit:
Node:
Drawings:
Design Intent:
No. Guideword Deviation Causes Consequences Safeguards Recommendations Action
by
Figure 12.5. Example HAZOP analysis worksheet
(enggcyclopedia)
Table 12.4. HAZOP overview
Typically Used
During Resource
Requirements Type of Results Advantages and
Disadvantages
Pilot plant operation
Detailed engineering
Routine operation
Expansion or
modification Material, physical, and
chemical data
Basic process
chemistry
Process flow diagram
Piping and
Instrumentation
Diagrams Scenario-based
documentation of
deviations, causes,
consequences,
safeguards, risk ranking,
and recommendations,
if any. Provides a structured
methodology to
systematically and
consistently analyze
hazard scenarios.
Provides input to Layer
of Protection Analysis
by identifying high
consequence
scenarios.
Potential for
redundancy in
covering hazards.
HAZOP, like the other hazard identification me thods, is a qualitative analysis. The higher
risk scenarios from a HAZOP analysis are frequently used as the foundation for a Layer of
Protection Analysis (LOPA). LOPA uses simplifying rules to evaluate initiating event frequency,
independent layers of protection, and conseq uences to provide an order-of-magnitude
estimate of risk. The primary purpose of LOPA is to determine if the scenario has sufficient
layers of protection to prevent or mitigate th e consequences. LOPA is discussed in Chapter 14
along with other risk assessment techniques.
Failure Modes and Effects Analysis (FMEA)
The FMEA method originated in the U.S. M ilitary where it was used to assess potential
equipment failures and reliability issues. The purpose of an FMEA is to identify single HAZARD IDENTIFICATION |
6.2 Assess the Organization’s Pr ocess Safety Culture |213
fam iliar with. Follow-up with a more general question
about how that role works.
Conduct the Interview. Work through the interview protocol,
using follow-up questions to clarify answers and to assure
com pleteness. Typically, interviewers will use three types of
questions:
Open-ended questions seek inform ation in the interviewee’s
own words. Questions like “What does a good process
safety culture m an to you?” and “What needs to be done to
reach your view of a good process safety culture?” allow
the interviewee to provide their opinion more fully. While
the answers to open-ended questions can be harder to
evaluate, their inform ation is more valuable. Open-ended
questions can sometimes lead to extraneous information
and tangential stories, which the interviewer can manage
with other forms of questions. Leading questions help steer the direction of the
conversation. A leading question like “Can you tell me
m ore about (the desired focus of the original question) can
be useful to bring a tangential question back on track.
However, avoid leading question like “You follow
procedures, don’t you?” These can sometimes direct the
desired answer or be perceived by the interviewee as a
trap. Closed questions seek concrete answers, typically “Yes” or
“No.” These provide the most precise information but limit
the respondent’s ability to provide valuable detail. For
exam ple, a closed question such as “Has the Alkylation Unit
PHA been revalidated yet?” m ay result in the answer “No.”
Once “No” has been stated, the interviewee may become
defensive and information m ay be lost. However, closed
questions like “Do I understand correctly what you said
that … ?” can be very useful to check understanding. Take
care to avoid close-ended questions that feel like a legal
cross-examination. •
•
• |
Piping and Instrumentation Diagram Development
406
3) Think about potential weakness points of the equip-
men
t. Consider these words: thin, tight, non‐metallic,
multi‐component part, expensive part, moving part, vibrating part, etc.
4)
Is the e
quipment sensitive toward suspended solids
and are there suspended solids in the incoming flow? If the answer is yes, a strainer may be needed upstream of the equipment.
5)
Is the e
quipment sensitive toward surged flow and is
the incoming flow likely to surge? If the answer is yes, a surge dampener may be needed upstream of the equipment.
6)
What i
s the plan if an off‐spec product is produced?
Can it be recycled or should it be discarded?
7) What
do you need to put in for easier inspection of
the equipment? You need to put more facilitating things if more frequent inspection is needed or if missing an inspection has large consequences.
8)
You mo
st likely need to put an isolation system (includ-
ing isolation valves) around your equipment unless you can not afford pulling off the operation of the equipment during the normal operation of the plant.
9)
What do you w
ant to do with incoming flow when the
equipment is non‐operational?
19.2.2 P&ID Dev
elopment: Control
and Instruments
After developing the piping and equipment portion, the
next step is the instrumentation and control portion. However, after finishing this task you may need to check the piping and equipment portion again. P&ID development, like other design processes, is not a straightforward process.
Here again we need to cover the four stages of opera-
tion. However instrument and control are mainly needed for the first two stages: normal operation and non‐routine operation of equipment.
For easy decision making a matrix similar to that
shown in Figure 19.2 can be developed for each piece of equipment. The different process and non‐process parameters are given in the first column and the different wrapping layers are placed in the first row. A check mark shows if it is decided to use each wrapping layer around each parameter.
Decision making for each steering loop was discussed
in detail in Chapter 16.However, here we provide a simple method as a
preliminary step.
To decide about parameters for each steering loop, all
the applicable parameters should be classified in five groups of “barely important parameters, ” “mildly impor -
tant parameters, ” “very important parameters, ” and “criti-cal parameters. ” Each importance level is connected to an I&C requirement: “nothing” for the first group, “monitor field” for the second group, “monitor control room” for the third group, “regulatory control loop” for the fourth group, and “safety interlock function” for the last group. Such correspondence is shown in Table 19.1.
There are some cases that a parameter is not definable
for a piece of equipment. For example, for a vessel flow rate is not definable. In some other cases a parameter is not important. For example composition generally is not important for pumps.
Barely important parameters are chosen based on
screening of the non‐important parameters and mildly important parameters.
Mildly important parameters are the parameters that
affect the operation of the unit but are not the main parameters of the unit.
Very important parameters are the parameters that are
related to the main duty of the unit.
Critical parameters are the parameters for which their
violation creates risk to personnel, assets and the envi-ronment. The increased risk could be through increasing the probability or consequences or both.
Table 19.2 shows a parameter matrix for a typical
pump in a hot water service.
In Table 19.2 different process parameters are exam-
ined against their criticality to come up with the required monitoring and control system. We generally don’t care about the temperature in pumps but as this pump works with hot water then there is chance of having cavitation when the temperature is high. It is a good idea to put a ICSS action
Parameter
Pressure
Temperaure
Flowrate
Level
Composition
MonitoringField
Control
Regulatory control
Interlock
Figure 19.2 St eering component selection matrix.
Raw material Conversion unit Seperation unitProduct
By-product
Figure 19.1 Pr ocess plant, a bird’s eye view. |
EQUIPMENT FAILURE 223
Piping
Most facilities have miles of piping. This pipi ng supports the flow of feed, product, and
everything in between to and from the equipment previously discussed in this chapter. Piping
comes in all sizes and materials. The piping materi al, the chemicals it is transporting, how it is
protected, and its routing are fact ors in how it may be damaged.
Figure 11.36. Piping rupture
(CSB 2015)
Example 1. Piping may corrode over time depending on the piping material and the
composition of the chemicals flowing through th e piping. An example of this is the Chevron
Refinery in Richmond, California suffered a fire in 2012 (Figure 11.36). The source of the fire
was a rupture of unit piping due to sulfidation co rrosion applicable at high temperature. Other
metallurgy and other chemical combinations can cause different types of corrosion.
Example 2. Through science and research, an im proved understanding may be gained
regarding the appropriate type of metallurgy for use with specific chemicals. Facilities that
were constructed years ago used the understa nding and materials of that time period. A
hydrofluoric (HF) acid alkylation unit with a piping elbow installed in about 1973 contained
more nickel and copper than would be recommended today in API RP 751 “Safe Operation of
Hydrofluoric Acid Alkylation Units” or in a Na tional Association of Corrosion Engineers (NACE
a) paper. The elbow failed resulting in a fire, expl osion, and release of toxic HF acid. Images of
the HF unit before and after the explosion and fire are shown in Figure 11.37.
|
274 INVESTIGATING PROCESS SAFETY INCIDENTS
Table 11.1 Human Factors Issues (cont.)
PERSONNEL FACTORS
Mental States Physiological States Physical/Mental
Focused attention Physiological state Reaction time
Complacency Physical health Vision/hearing
Distraction Influence by medication Knowledge
Mental fatigue Physical capability
Haste Fatigue
Situational awareness
Motivation
Task saturation
Language/cultural differences
Shift cooperation/teamwork
WORKPLACE FACTORS
Design Maintenance Environmental
Instrumentation clarity Poorly maintained equipment Illumination / visibility
Layout work space, access Poorly maintained workspace Storm
Communications equipment Poorly maintained
communications equipment Temperature (hot or cold)
Equipment provided for the job Labeling Wind
Noise level
Incident investigations must include human performance
considerations and human fa ctor issues. The use of ch ecklists and flowcharts
is a helpful technique to aid investigators i n addressing human
performance issues. For example, checklists can be built using the
information in the tables shown above in this section. Checklists may be
strengthened with input from a human psychologist, an expert on human
reliability analysis, and experienced incident investigators. Numerous
interface devices have been developed that translat e theoretical models of
human error causation into easy-to- understand engineer ing terms. Some
of these devices are in the form of logic trees or checklists.
Chapter 10 describes the use of checklists in root cause analysis.
|
INVESTIGATION M ANAGEM ENT SYSTEM 49
4.1 SYSTEM CONSIDERATIONS
4.1.1 An Organization’s Responsibilities
Incident investigation is only one of the many elements of a process safety
management program (CCPS, 2007), and is notably one that plays an
essential role in identifying overall management syst em weaknesses on a
continuous basis. Establishing a high quality incident investigation program
begins with management’s support, comm itment, and action. To
demonstrate support, it is common pr actice to establish a written policy
regarding incident notification, investigation, and dissemination of findings; to communicate this policy to the workforce;
and to sustain the policy over
time by committing resources for continuous improvement (see Chapter 15). This is often expressed in a formal statement
written to achieve the following
goals.
• Communicate management’s commitment to prevent recurrences by
determining causal factors and root causes, evaluating preventive measures,
and taking follow-up action.
• Recognize the importance of implementing investigation findings as a strategic risk control mechanism.
• Strongly support reporting and investigating near-misses.
• Clearly focus on finding causal fa ctors, root causes, and management
system weaknesses, while avoiding assignment of blame.
• Endorse sustained commitment of resources for the investigation
program, including training team members. This supports employee
participation in the investigation program and the appropriate and
timely implementation of recommendations.
• Emphasize the value and necessity of communicating and sharing the
lessons learned from the investigation to all that could reasonably
benefit.
• Support a system to ensure that all recommendations and findings are
resolved and that decisions and actions are documented.
• Establish a mechanism to fo ster continuous improvement.
Management demonstrates support fo r this policy by nurturing an
atmosphere of trust and respect that encourages openness in reporting
incidents throughout the organization. Failure to achieve this positive
atmosphere may result in hidden incide nts and low or no reporting of near-
misses, which results in lost learning opportunities that could have
potentially led to avoida nce of future accidents.
|
8
inherent safety in determining the r oot causes of an incident. By means
of an illustrative example, Gupta et al . (Ref 1.7 Gupta) provided evidence
of the linkages between inherent safety and the cost of process safety.
Their work helps to establish a clear bu siness case for the use of inherent
safety principles in management ef forts directed at enhancing process
safety.
Further motivation for the curre nt research is found in the
comments of employees who have reviewed the field of inherent safety and inherently safer design, including (Ref 1.3 Bollinger), (Ref 1.7 Gupta),
(Ref 1.12 Kletz), (Ref 1.10 Khan) and (Ref 1.26 Vaughen 2012b). For example, Khan and Amyotte (Ref 1.10 Khan) have remarked that the various elements of process safety management can be seen to have at least a partial basis in inherent safety . This fact has been recognized by
companies that have incorporated inhe rent safety as a “named feature”
in their safety management document ation and have developed internal
standards for the use of inherent safety principles. Yet the term inherent
safety is typically not named as such in the general description of process
safety management systems. Per Bo llinger, et al. (Ref 1.3 Bollinger),
explicit use of inherent safety te rminology within such management
systems is a possible means of furtheri ng the adoption of inherent safety
principles in industry.
Over the years, the interest in inherent safety from government,
industry, and the public has increase d. Inherent safety’s promise has
produced heightened expectations and it is seen almost as a panacea to
reducing risks in the chemical proces s industries as the public becomes
aware of the concept. Inherent safety is incorporated into safety and security regulations in pa rts of the United States at the local, state, and
federal levels. Inherent safety has been proposed as a leading
requirement for chemical security re gulations in the U.S. Congress. To
better clarify and more precisely define the terminology, the US
C h e m i c a l S e c u r i t y A n a l y s i s C e n t e r ( C S A C ) o f t h e D e p a r t m e n t o f Homeland Security (DHS) contracted with CCPS to provide a technology-based definition of Inherently Safer Technology (IST) (Ref 1.4 CCPS/DHS).
Some of the best compilations of in formation on IS can be found in
the works of (Ref 1.14 Kletz 1978), (Ref 1.15 Kletz 1996), (Ref 1.16 Lees) and the final report of the INSIDE (INherent SHE in DEsign) project in |
REACTIVE CHEMICAL HAZARDS 99
Chemical Reactivity Worksheet (CRW)
The Chemical Reactivity Work sheet (CRW) is a free software program providing extensive
process safety information (Refer to Sectio n 2.5) The CRW includes data required to
understand the hazards associated with the inadvertent and intentional mixing of reactive
chemicals. This includes the chemical reactivity of thousands of common hazardous chemicals,
compatibility of absorbents, and suitability of mate rials of construction in chemical processes.
It is designed to be used by emergency resp onders and planners, as well as the chemical
industry, to help prevent hazardous chemical incidents. It is available at
https://www.aiche.org/ccps/resour ces/chemical-reactivity-worksheet . (CCPS)
Versions of the CRW were developed by th e collaboration of several organizations
including the Center for Chemical Process Sa fety, Environmental Protection Agency, NOAA's
Office of Response and Restoration, The Ma terials Technology Institute, Dow Chemical
Company, Dupont, and Phillips.
The CRW contains a database of chemical datasheets for thousands of chemicals. The
chemical datasheets in the CRW database cont ain information about the intrinsic reactive
hazards of each chemical, such as flammability, the ability to form peroxides, the ability to self-
polymerize, explosivity, strong oxidizer or reducer capability, water or air reactivity,
pyrophoricity, known catalytic activity, instabilit y, and radioactivity. Datasheets also contain
general descriptions of the chemicals, physical properties, and toxicity information. They also
include case histories on specific chemical inci dents, with references. The CRW also allows the
creation of custom chemical datasheets, for ex ample, to use in documenting properties of a
proprietary chemical that is not in the CRW database.
The CRW uses chemical pairs. In order to fully understand inadvertent and intentional
mixing, the reactivity of the entire mixture must be understood, not just the pairs.
The CRW includes a reactivity prediction worksh eet to virtually "mix" chemicals to simulate
accidental chemical mixtures, such as in the case of a train derailment, to learn what dangers
could arise from the accidental mixing. For exampl e, if the reaction is predicted to generate
gases, the CRW will list the potential gaseous products, along with literature citations.
The CRW has two additional modules of particul ar interest to the chemical industry. One
of them discusses known incompatibilities between certain chemicals and common
absorbents which are used in the cleanup of small spills. The other module, new in CRW 4,
contains information about known incompatibilit ies between certain chemicals and materials
that are used in the construction of containers, pipes, and valving systems on industrial
chemical sites.
The Mixture Manager screen provides a search for chemicals in the CRW's database, a
preview of the information on the chemical datash eets, and the creation of virtual mixtures of
chemicals. It also provides access to all the ot her features of the program from this screen,
including the compatibility chart and hazards report for any mixture created, reference
information about the reactive groups used in the CRW, and information about absorbent
incompatibilities with certain chemicals.
The Compatibility Chart shows the predicted hazards of mixing the chemicals in a
mixture in an easy-to-use graphical interface. The reactivity predictions are color-coded, and |
465 |
FIRE AND EXPLOSION HAZARDS 69
Figure 4.14. Relationships between the different types of explosions
(Crowl 2003)
Table 4.3 provides examples of the types of ex plosions. You can observe that some incidents
can involve multiple types of explosions, for example a vessel rupture leading to a BLEVE.
Physical Explosion - The catastrophic rupture of a pressurized
gas/vapor-filled vessel by means ot her than reaction, or the sudden
phase-change from liquid to vapor of a superheated liquid
(CCPS Glossary)
Boiling Liquid Expanding Vapor Explosion (BLEVE) A type of rapid
phase transition in which a liquid contained above its atmospheric
boiling point is rapidly depressurized, causing a nearly instantaneous
transition from liquid to vapor with a corresponding energy release. A
BLEVE of flammable material is often accompanied by a large aerosol
fireball, since an external fire impinging on the vapor space of a
pressure vessel is a common cause. However, it is not necessary for the
liquid to be flammable to have a BLEVE occur. (CCPS Glossary) |
308 | Appendix E Process Safety Culture Case Histories
explosion that resulted in injuries to personnel and significant
property dam age to the facility.
In the investigation that followed, the operator stated that he
did not feel com fortable taking SWA action and that a supervisor
should have been there to m ake that call. When asked why he was
not comfortable, the operator responded that in over the years,
when SWA was used, there had been a lot of second-guessing by
investigators after the fact.
Further review showed that the incident investigation reports
described alternative actions that the operators could have taken
in response to the indications they were receiving at the control
board that would have abated the transient but kept the process
running. Som e reports also suggested disciplinary action,
although none was taken.
When operators exercise SWA, it is certainly possible that
options existed for them to bring the process under control. B ut
under duress, it is hard to know if such an option exists or not,
which is why SWA is so important. How can incident investigators
address potential alternative actions without underm ining SWA?
Foster Mutual Trust, Combat the Normalization of Deviance.
E.23 SWPs by the N um bers
Safe work permits are involved activities used to
help ensure that the hazardous work is fully
prepared before any work begins. In a large facility,
these permits (e.g. Safe Work, General Work, Hot Work, Confined
Space Entry, Line Breaking, and others) had been issued by the
on-duty operators. The very large num ber of perm its being
sought at the beginning of day shift would overwhelm the board
operator and com pletely distract him from running the
equipment. To address this problem, the company appointed a
set of perm it approvers especially for this “rush hour.”Actual
Case
History |
52 GUIDELINES FOR MANAGING ABNORMAL SITUATIONS
3.3.5 Additional RBPS Elements Related to Management of
Abnormal Situations
The RBPS elements in this section ar e briefly discussed in this chapter
for awareness. Some of them, such as MOC, will be discussed in Chapter
5.
3.3.5.1 Compliance with Standards
Includes applicable regulations, standards, codes, and other
requirements issued by nation al, state/provincial, and local
governments, consensus standards or ganizations, and the corporation.
Interpretation and implementation of these requirements include
development activities for corporate, consensus, and governmental
standards.
3.3.5.2 Process Safety Competency
Addresses skills and resources that the company needs to have in the
right places to manage its process haza rds. Provides verification that the
company collectively has these skills and resources and applies this
information in succession planning and management of organizational
change.
3.3.5.3 Asset Integrity and Reliability
Activities to ensure that importan t equipment remains suitable for its
intended purpose throughout its serv ice. Includes proper selection of
materials of construction; inspec tion, testing, and preventive
maintenance; and design for maintainability.
3.3.5.4 Management of Change
Process of reviewing and authoriz ing proposed changes to facility
design, operations, organization, or activities prior to implementing
them, and updating the process sa fety information accordingly.
3.3.5.5 Conduct of Operations
Means by which management and operational tasks required for
process safety are carried out in a deliberate, faithful, and structured
manner. Managers ensure workers carry out the required tasks and
prevent deviations from expected performance: |
182 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
Figure 11.2. Buncefield storage depot before the explosion
(HSE 2017)
Figure 11.3. Buncefield Terminal site and wider area after explosion
(HSE 2017)
|
Documenting and Following Up on a PHA Revalidation 165
8.5 PRINCIPLES FOR SUCCESSFUL DOCUMENTATION AND
FOLLOW-UP
Actual experience in conducting revalid ations, by PHA practitioners across a
number of companies, has highlighted so me keys for success, as well as some
things that can impede success. While none of the items listed are absolute rules,
they do provide valuable guidance.
Successful Practices:
• Documenting the revalidation to maximize its value to future users
• Documenting the PHA in a way that simplifies future revalidations
(e.g., facilitating the Update approach)
• Describing complete loss scenarios, from initiating cause, through
intermediate events, to potential consequences
• Documenting the changes made in an Update clearly (e.g., by using
a distinct font color, using software features to track changes, or
making detailed annotations in a comment column)
• Consolidating the core, complementary, and or supplemental
analyses, along with any relevant portions of prior PHAs in a single
revalidated PHA document that satisfies both regulatory and
organizational requirements
• Writing recommendations that are clear to people who did not
participate in the revalidation
• Minimizing the time between the PHA team developing
recommendations and communica ting them to management
• Resolving recommendations as soon as possible/practical
• Retaining a complete set of records for the next revalidation
Obstacles to Success:
• Documenting team discussions with abbreviated or cryptic notes,
or using terminology unfamiliar to operating personnel
• Leaving blanks in worksheets, tables, or checklists
• Having no clear rationale for Update vs. Redo documentation style
• Documenting the PHA in Update style when a Redo is performed
• Using Update documentation on many sequential revalidations
• Failing to revise all the core, complementary, and supplemental
study documentation affected by the revalidation |
140 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
New engineer activities on this topic will depend on their working location. Coastal
locations may have exposure to hurricanes and associated flooding, while other areas may be
concerned with wind and wildfires. Northern loca tions such as Canada and Alaska will be most
concerned about very low temperatures. Desert locations may need to address sandstorms.
Locations such as California and Turkey sh ould address earthquake preparedness as
demonstrated by the Fukushima incident.
Tools
Kinetic and potential energy hazards ca n be identified and managed through
use of engineering tools learned in undergraduate engineering curriculum.
CCPS Monograph: Assessment of and planning for Natural Hazards. lists many data sources
and approaches for identifying meteorological and geological hazards and addressing them in
design and emergence response preparedness plans. (CCPS 2019) The monograph includes
reference to the following data sources and design criteria.
Data sources.
• Federal Emergency Management Agency (FEMA) flood maps -
https://msc.fema.gov/portal/home
• United States Geological Survey (USGS) seismic maps -
https://earthquake.usgs.gov/hazards/designmaps/usdesign.php
• American Society of Civil Engineers (ASCE) seismic guide -
https://hazards.atcouncil.org/#/
• National Oceanic and Atmospheric Adminis tration (NOAA) tornado prediction -
https://www.spc.noaa.gov/new/SV Rclimo/climo.php?parm=allTorn
• Tornado Wind Prediction - https://hazards.atcouncil.org/#/ (ATC)
• National Hurricane Center (NHC) Storm surge maps -
https://www.nhc.noaa.gov/nationalsurge/ (NHC and NOAA 2019 a)
• Snow load - https://hazards.atcouncil.org/#/ (ATC)
• NOAA Hurricane center - https://www.nhc.noaa.gov/climo/
Design guidance.
• ASCE Flood Resistant Design and Construction, ASCE 24 (ASCE 2014)
• ASCE Minimum Design Loads and Associated Criteria for Buildings and Other
Structures, ASCE /SEI 7-16 (ASCE 2016)
• CCPS Guidelines for Safe Warehousing of Chemicals (CCPS 1998)
• CCPS Guidelines for Safe Storage and Handling of Reactive Materials (CCPS 1995)
• Guidelines for Siting and Layout of Facilities, 2nd Edition (CCPS 2018)
• FM Global Property Loss Prevention Data Sheets 1-2 Earthquakes (FM Global 2021) |
Appendix 215
Other References in Table A.2-2
o (Behie 2008) Dolphin Energy [44]
o (Bloch 2016) Bhopal [95]
o (EPA 2018) Tosco Avon Refinery [118]
o (EPSC 2019) Flare System [119]
o (Fogler 2011) Monsanto [62]
o (Meshkati 2014) [77]
o (NFPA 2011) Hydrocracker Excursions [120]
o (UK HSE 1997) Texaco Pembroke [68]
|
4.5 Process Safety Culture Metr ics |145
m eetings including substantial discussion of process
safety. An imbalance in emphasis m ay be indicative of a
m anagement attitude that process safety is less important.
Frequency with which relevant process safety statistics are
shared with the organization. A low value m ay indicate that
m anagement does not adequately appreciate the value of
informing the workforce of the organization’s process
safety perform ance. Manager attendance at management review meetings.
Poor attendance m ay indicate a low interest in process
safety perform ance, or in communicating m anagement
expectations.
Foster Mutual Trust This core principle can be subjective, and leaders and
workers may have a different opinion regarding trust.
Those opinions may be difficult to elicit from fixed surveys.
Therefore, this core principle should be assessed primarily
by interviewing leaders and workers. Generally, the
interviews should consider whether interviewees feel that:
o A just system exists where honest errors can be
reported without fear of reprisals,
o Submitted information will be acted upon,
o B ad ideas can be challenged, discussed, and resolved
satisfactorily; and
o Errors will not be punished unless the act was reckless,
deliberate, or unjustifiable. Since trust between peers is also im portant, the sam e
approach can be applied to peer interactions.
Ensure Open and Frank Communications
Do employees exercise stop-work authority? When they
do, does leadership thank them and take care to avoid
second-guessing their decisions? •
•
•
•
• |
Overview of the PHA Revalidation Process 21
1.8 RELATIONSHIP OF RBPS PILLARS TO A PHA
REVALIDATION
The RBPS book [3] describes the RBPS approach and recognizes that not all
hazards and risks are equal. It advocates that resources should be focused on
more significant hazards and higher risks. The RBPS approach is built on the four
accident prevention pillars. Included is a summary of how PHA revalidation is
related to each pillar and its associated elements. For detailed information on
the RBPS accident prevention pillars an d their elements, see the RBPS book:
Commit to Process Safety . Process safety culture is generally defined as “How
we do things around here” or “How we behave when no one is watching.” In a
facility or company with a strong process safety culture, a PHA revalidation is an
important and highly valued exercise.
In order to meet the process
safety goals of an organization, a
revalidation team consists of a
diverse team of well-trained
process experts who understand
the importance and value of the
revalidation.
Conversely, in a facility where
process safety culture could be
improved, the PHA revalidation
exercise is seen as a rote task that
must be completed (e.g., to satisfy
regulatory or company require-
ments). The goal for such a PHA is to be able to claim it was done on time but
required little or no effort to perform and created minimal additional work for
follow-up.
Understand Hazards and Risk. Process knowledge is a critical key to the
success of any PHA revalidation and includes both process documentation and
the competency of process experts (wit h many areas of experience including
operations, engineering, and applicatio n of PHA methods). A revalidated PHA
that incorporates current knowledge of the process and its hazards is
foundational for all the other RBPS elements that rely on the PHA, such as the
asset integrity of safety-critical equi pment, MOC, or emergency response
planning. Process Safety Culture
In a facility with a strong process
safety culture, there is trust that the
PHA revalidation will be of value and
the results of the study will be acted
upon. This trust and outreach/
communication flows from opera-
tions, through the PHA revalidation
team, to management, and then back
again. |
302 Human Factors Handbook
23.2.2 Why did this happen?
This incident had multiple causes. The Ch emical Safety Board report noted that:
• Repairing a cracked seal loop was po stponed (allowing vinyl fluoride to
flow to the slurry tank).
• The equalizer line, which provided the direct path for the flammable
vapor to enter tank 1, was not blinded and was not included on the lock
out card for the slurry tank.
• The hot work permit procedure did not require testing the atmosphere
inside the tank.
There were issues with the role of contractor management, which are
discussed next.
DuPont recognized that contractors ma y be unfamiliar with process safety or
activities on their sites. DuPont’s inte ntion was to ensure that everyone would
understand the work and potential hazards. In this instance, DuPont intended that
the construction field engineer and the area manager would help the contractor
understand the hazards.
The contractor submitted a “hot work permit”. However, the section of the
permit which asked if flammable material would be within 35 feet (10 meters) of
the work was not completed. The hot work was within 35 feet (10 meters) of the
slurry flash tank that vented vinyl fluoride to the atmosphere.
It was concluded that:
“The contractors were unfamiliar with the Tedlar® process and the process
equipment involved. The contractors did not know what the slurry flash tank
was or which chemicals were presen t inside it.” p10, CSB [98]
The permit was signed off by the DuPont construction engineer and by the area
manager. It was reported that:
• The DuPont construction engineer for the slurry tank work had no
working knowledge of the Tedlar® process.
• The construction engineer expected the area manager would advise the
contractors of plant-specific proce ss safety information for hot work.
• An area manager signature was ob tained by someone in a service
department. The area manager lacked knowledge of the area and of the
Tedlar® process. In addition, they did not perform the required “walk
down” of the area before signing the permit.
• The area manager assumed the constr uction engineer was briefing the
contractors on-the-job and the hazards.
|
5.5 References | 67
6.Prepare. The evaluator works with peers to develop an action plan to
implement the changes. The plan includes resources, capital, training,
communication, and other key factors.
7.Implement. After company leadership has endorsed the plan, the plan is
implemented. The implementation team may include both corporate
experts and site leaders. Implementation includes leadership, workforce
involvement, training, conduct of operations, metrics, and ongoing
management review.
8.Embed and Refresh. Company and site leadership now manage
according to the changes as implemented. Ongoing communications and
training remind, maintain the sense of vulnerability, and reinforce the
need to maintain the new way of doing things.
These components of the REAL Model will be described in greater detail in
chapters 6 and 7. Chapters 9–14 will provide some hypothetical examples of
how the REAL Model may be used.
5.5 References
5.1 CCPS (2019). Process Safety Leadership from the Boardroom to the
Frontline. Hoboken, NJ: AIChE/Wiley.
5.2 Gardner, H. (1995). Reflections on multiple intelligences: myths and
messages. Phi Delta Kappan 77: 200–209.
5.3 Gardner, H. (2011). Frames of the Mind: The Theory of Multiple
Intelligences. New York: Perseus Books Group.
5.4 Hiatt, J.M. (2006). ADKAR: A Model for Change in Business, Government, and
Our Community. Fort Collins, CO: Prosci Learning Center Publications.
5.5 International Association of Oil & Gas Producers (2016). Components of
Organizational Learning from Events. IOGP Report No: 552.
5.6 Joshi, S. (2009). How we learn and grow. blog.practicalsanskrit.com/
2009/12/how-we-learn-and-grow.html (accessed January 2020).
5.7 Kotter, J.P. (2012). Leading Change. Brighton, MA: Harvard Business
Review Press.
5.8 Levasseur, R.E. (2001). People skills: Change management tools—
Lewin’s change model. FOX Consulting Group Newsletter, July-August
2001.
5.9 Lombardo, M. M. and Eichinger, R. W. (2010). Career Architect
Development Planner, 5th Edition. Minneapolis, MN: Lominger. |
28 PROCESS SAFETY IN UPSTREAM OIL & GAS
Other hazardous chemicals present onshore or offshore include methanol if used
for flow assurance (flammable and toxic), glycols (e.g., TEG) for dehydration,
corrosion and other inhibitors, acids for various treating, and amines (MEA, DEA,
MDEA) for H 2S and carbon dioxide (CO 2) removal. H 2S separated from amine
solutions can be almost pure and is ve ry hazardous. Storage may be required for
diesel fuel for emergency generators, fire pumps and jet fuel for helicopters. An
environmental issue relates to naturally occurring radioactive materials (NORM)
which may leach from the formation and be transported to the surface in produced
water, oil and gas. These can precipitate ou t and form solid waste. Dumping of these
locally is not permitted.
There are multiple chemicals used for well stimulation and water flood, but
these normally do not pose a process safety ri sk. An exception is the use of hydrogen
fluoride (HF) which is very toxic as well as flammable. Getting it mixed and
delivered to a well, safely injected, and the returns properly handled, is a challenge.
2.5 WELL WORKOVERS AND INTERVENTIONS
During the plateau and decline phase of the well (Figure 2-1), the composition of
produced fluids changes. Ma ny reservoirs flow naturally initially because of the
reservoir pressure and the gas content. In itially lighter materials may dominate, but
over time the reservoir pressure generally decreases, heavier components may
increase, and produced water may also increase. Also, in some cases sand can be
produced. While initial flows may be free flowing, the change in reservoir
characteristics to heavier materials may requ ire some form of flow assistance (i.e.,
artificial lift) to prod uce the well – either gas lift or water injection into the reservoir
to maintain reservoir pressure. Other forms of enhanced oil recovery are possible
using, for example, hydrocarbons, heat, or carbon dioxide. It may also be feasible to
increase production and do well maintenance through workovers or interventions.
Process Safety Issues
There are process safety implications when the well is opened for workover or
intervention. Many aspects of risk are similar to well construction (see Section 2.2),
including loss of well control or blowout. The likelihood may be lower if the
pressure is reduced due to reservoir depletion.
2.6 DECOMMISSIONING PHASE
The end-of-life stage of a we ll is reached when flow rates produced are no longer
economical and it is decided to abandon the well.
The proper plugging and abandonment of an onshore or offshore well is defined
by regulators globally. While differences exist, they all seek to accomplish the
following.
1.Isolate and protect all subsurface freshwater zones |
13 2
The Upstream Industry
2.1 UPSTREAM INDUSTRY
2.1.1 Life Cycle Stages
This chapter provides an overview of the upstream industry and follows the
upstream life cycle. Greater details on we ll construction, well work, and onshore
and offshore production are provided in Chapters 4, 5 and 6, respectively. Engineering design, construction, and installation are covered in Chapter 7. The main life cycle stages are shown in Fi gure 2-1 and are described as follows.
●Exploration and Well Construction, including discovery and appraisa
l
wells
●Engineering design, construction and installation
●Production phase (covering first oil, build-up, plateau and decline)
●Well workovers and interventions to maintain well integrity and boos t
production during decline
●Decommissioning / abandonmen t
The complete life cycle is more comple x than the figure shows as additional
wells may be constructed and well stimulation activities or other enhanced oil recovery methods may be implemented to maintain production levels.
Figure 2-1. Typical upstream life cycle Exploration well
Appraisal Well
First Oil
Build-upPlateau
Decline
Abandonment
Economic limitProduction
TimeProcess Safety in Upstream Oil and Gas
© 2021 the American Institute of Chemical Engineers |
386 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
The design was based on chalk drawings on th e workshop floor. No engineering review by
a qualified mechanical engineer was undertaken to review the mechanical adequacy of the
connection. The investigation found that “No co nsideration was given to the bending moments
or hydraulic thrusts that would be imposed on the assembly due to its dogleg design. There
was no reference made to vendor manuals for the expansion bellows, no r to relevant British
Standards. No drawing was made for the design.” (HMSO 1975).
Lessons
Management of Change. Changes to a process or equi pment must be reviewed and
implemented by people with knowledge appropriate to the situation. This incident is important
in the history of process safety as the prime example of the importance of an MOC program.
The site made no engineering review of this ch ange. As seen in the cause section, important
mechanical design features were not considered during the change.
Flixborough highlights the importance of Manage ment of Organizational Change (MOOC)
as well as physical change. At Flixborough, “the works engineer had left early in the year and
had not yet been replaced. At the time the by pass line was being planned and installed, no
engineer was on site with the qualifications to perform a proper mechanical design, or to
provide critical technical review on related issues. There were chemical and electrical
engineers on staff, but no other mechanical engineers.” A statement often used in relation to
the modifications at Flixborough is that “they didn’t know what they didn’t know”. Although the
presence of a mechanical engineer may not ha ve changed the outcome if no MOC review was
held, it is more likely that the significance of the change could have been recognized by
someone at the plant. MOOC covers modification of work schedules, personnel turnover, task
allocation changes, organizational hierarchy changes, and organizational policy changes.
Guidelines for Managing Process Safety Risks During Organizational Change (CCPS 2013) covers
this topic in more detail.
Compliance with Standards. As stated in the summary, the site office building was
destroyed. At the time, 1974, no facility siting and layout standards existed. This event is an
example of why such a standard, API RP 752, “Management of Hazards Associated
with Location of Process Pl ant Buildings” was developed.
Introduction to Management of Change
Much thought goes into the design and engineering of a facility to support it operating safely.
T h i s i n c l u d e s a d e s i g n r e v i e w w i t h P H A , a pre-startup safety review, sound operating
procedures, and ongoing mechanical integrity processes. Management of change addresses
any changes in design, equipment, and operation. Examples of types of changes are given in
Table 18.1.
One of the key things to understand is what constitutes a change. Many things may be
changed over the life cycle of a facility for exam ple, to improve operations, expand production,
add new products, and replace worn equipment. The one example that is not a change is
replacement-in-kind. This deserves a clos e review as changes that may seem like a
replacement-in-kind may have minor variations that warrant consideration as a change. |
120 | 4 Applying the Core Pr inciples of Process Safety Culture
his previous position, the only time Congress ever directly
intervened in the employment of a government contractor.
Managing Ethics
Ethical behavior is not an innate activity. Ethics can, and
should, be m anaged. Many com panies define standards guiding
ethical behavior that is encouraged as well as unethical behavior
that is not tolerated. Likewise, professions and professional
societies, as well as trade organizations, have had similar codes
for decades and even centuries. Codes generally represent high-
level aspirations of conduct, and establish consistent expectations
for the conduct of m embers of the group. M oreover, they declare
to the public the behavioral expectations of the group.
Organizations associated with process safety that have ethical
codes include the Board of Certified Safety Professionals, the
B oard of Environmental Auditor Certification, and the National
Society of Professional Engineers, among others. The American
Institute of Chemical Engineers (AIChE) stands out am ong
technical societies for its Code of Ethics. The pream ble to AIChE’s
code states (Ref 4.9):
“Members of the American Institute of Chemical Engineers shall
uphold and advance the integrity, honor, and dignity of the
engineering profession by: being honest and impartial and serving
with fidelity their employers, their clients, and the public; striving
to increase the competence and prestige of the engineering
profession; and using their knowledge and skill for the
enhancement of human welfare.”
The AIChE code goes on to address three topics closely related
to process safety culture: (1) Hold paramount the safety, health and welfare of the
public and protect the environment in performance of • |
Conducting PHA Revalidation Meetings 133
The main difference between a Redo and an Update is the starting point. In
a “pure” Redo , the meeting is conducted in a ma nner similar to the initial PHA.
More often, the team makes some use of the previous PHA documentation if it
is of high quality. For example, the previ ous PHA may be used as a checklist. As
the current team concludes its discussion of a particular loss scenario, the team
might look at (or display) the previou s PHA and ask, “Is there anything we
missed?” The differences might be factual (e.g., the previous team included a
cause that the current team overlooked) or judgmental (e.g., the previous team
took credit for a safeguard that the current team judged ineffective). Regardless,
the study leader should continue the team discussion and resolve any
discrepancies before moving to the next topic.
Extensive use of the previous PHA is possible as long as it does not
compromise the reason the Redo approach was selected. For example, perhaps
the PHA is being Redone simply because the study leader believed it was the
more efficient approach, given the large number of changes that affected most
of the nodes. With no indication that the previous PHA was deficient, the study
leader might pre-populate the revalidat ion worksheets with some information
from the previous PHA and use it to expedite the current discussions as if it were
an Update . On the other hand, if the Redo approach was selected because the
organization truly wanted a fresh look at the risks of the entire process, such
extensive use of the previous PHA migh t seriously compromise achievement of
that goal. In any case, the revalidation team should be fully involved in
developing and analyzing loss scenarios. The facilitator should ensure that any
pre-populated entry is discussed, and th at additional brainstorming is allowed
(and encouraged) beyond those borrowed entries.
Updating the Core Analysis. The Update approach is usually selected when
there are relatively few, specific changes in the process equipment or
procedures, and the core methodology, existing node definitions, and risk
tolerance criteria are unchanged. In that case, the revalidation approach is
relatively simple and quick to apply, but it still requires thoughtful consideration.
The revalidation leader guides the team through the existing documentation,
soliciting the team to either confirm or correct the current information. The
more detail (e.g., specific valve or instrument numbers) documented in
worksheets of the prior PHA report, the easier it is to Update . (If the prior PHA
lacks such detail, the team should cons ider adding it to facilitate future
revalidations.) When known changes are encountered, the team appropriately
edits the affected documentation. Even if there are no known changes, the team
should critically evaluate each node for technical accuracy and thoroughness in
identifying hazards. The previous team may have made a mistake, a change may
have eluded the management of change system, a safeguard relied upon by the
previous team may no longer be effecti ve, or incidents may have shed new light |
Heat Transfer Units
203
Each enclosure is for each stream, one for a cooling
stream and the other one for a heating stream.
To refer to each of these enclosures we have to use
better terminology than “closure one of the heat
exchanger” and “closure two of the heat exchanger. ”
In S&T HXs, a stream flows inside of tube and the
other stream flows outside of the tubes or in shell. Therefore we can name the former enclosure the tube‐side and the latter the shell‐side.
This applies specifically to S&T HXs. The other
types of heat exchangers don’t have shells and tubes but they still have two enclosures. Table 11.2 lists the terminology for the two enclosures in different types of heat exchangers.
11.4 Different Types of Heat
Tr
ansfer Fluids and Their Selection
As it was mentioned before we have two types of heat exchangers of process heat exchangers and utility heat exchangers, and process heat exchangers have higher priority for use in plants.
We can, then, say the best heat transfer fluid is the
existing process fluid and then utility fluids.
Amongst cooling utility streams the best fluids are air
and water, which are abundant resources. Therefore they are on the top of the list of preferred utilities. If they cannot be used the other options can be considered.
If sea water is available it could be very attractive
choice for cooling.
A list of cooling streams is given in Table 11.3.For heating purposes the fluids on the top of list are
hot water and steam.
A list of heating streams is given in Table 11.4.If the temperature of the target stream needs to be
increased to more than 400
°C, t
he only choice is probably
a fired heater.
Using steam as a source of heat in heat exchangers is
very common. However there are some points regarding the usage of steam as a heat transfer medium.The first point is that only saturated steam, and not
superheated steam, can work as the heat providing fluid. If superheated steam is available, and it is intended to be used for heating purpose in a heat exchanger, it should be converted to saturated steam before usage. A superheated steam is nothing except a “gas, ” but it can be converted to a heating medium through a desuperheater.
The second point is that it should be ensured that
the steam is completely “used” in the heat exchanger before leaving it. The complete usage of steam means complete conversion of the steam to condensate. We have to make sure there is no amount of steam remaining in the stream exiting a heat exchanger. This can be done by a placing steam trap on outlet side of the hot fluid of the heat exchanger.
Using steam as a heat transfer medium is economically
justifiable when the required temperature of the heat transfer medium is less than 150 °C. When the required Table 11.2 Ter minology of twin enclosures in heat exchangers.
Heat exchanger type Enclosure Name
Shell and tube (S&T) heat exchanger Shell side, tube side
Double pipe heat exchanger Pipe side, annular side
Plate and frame (P&F) heat exchanger Hot side, cold sideSpiral heat exchanger Hot side, cold side
Aerial cooler Tube sideTable 11.3
Utilit
y stream choices for cooling.
Cooling streams Application
Cooling by air in
aerial coolerWhen cooling down to approximately 65
°C is
ade
quate
Cooling by “cooling water” or “cold glycol”When cooling down to 65
°C
is not enoug
h but down to
approximately 40 °C is
ade
quate
Cooling by “chilled water”When cooling down to 40
°C
is not enoug
h but down to
approximately 20 °C is
ade
quate
Cooling by “refrigerated water”When cooling down to 20
°C
is not enoug
h but down to
approximately 10 °C is
ade
quate
Table 11.4 Utilit
y stream choices for heating.
Heating streams Application
Heating by hot water or hot glycolWhen heating up to approximately 100
°C is
ade
quate
Heating by steam or “hot glycol”When a heating up to 100
°C is not enoug
h but up
to approximately 150 °C is
ade
quate
Heating by non‐water based hot liquidsWhen heating up to 150
°C
is not enoug
h but up to
approximately 400 °C is
ade
quate |
2. Human performance and error 15
A Human Factors principle is that it is vital to ask how and why errors occur.
This includes asking:
• How an individual’s performance is influenced by the conditions they
work in;
• Whether the information and equi pment they have been given are
suitable and sufficient;
• Whether the training they have been given is sufficient; and
• How an individual’s performance is influenced by the prevailing culture.
An understanding of human errors and mistakes makes it possible to identify
how to reduce the possibility they o ccur. Consequently, it enables the
improvement of human performance.
2.3.3 Performance influencing factors and human error
Many factors contribute to an individual or a team making a mistake. These include
the operator’s level of experience, the complexity of a task, the clarity of operating
instructions, the duration of working hours, organizational culture, as well as many
others. These factors are sometimes called Performance Influencing Factors
(PIFs). Some common PIFs are illustrated in Figure 2-2.
Directors, managers and
supervisors should identify which of
these factors influence the
performance of a particular task. It is
then possible to create conditions to
successfully carry out tasks. Later
Chapters in this handbook provide
advice on creating these conditions.
“Performance Influencing Factors (PIFs)
are the characteristics of the job, the
individual and the organization that
influence human performance.”
UK Health and Safety Executive [4] |
AN INTRODUCTION TO PROCESS SAFETY FOR UPSTREAM 7
4.This book can help upstream personnel improve their understanding and
communication of the concepts of process safety management.
1.5 SCOPE OF THIS BOOK
The upstream oil and gas industry is diverse. This concept book provides an
overview of process safety as it applies in the upstream industry. Hopefully, this
book will spur the interest in developing subsequent, more detailed, guideline texts.
After this Introduction chapter, this book provides an overview of upstream
operations in Chapter 2, including an introduction to safety barriers, and a short
review of international regulations. This is followed by a summary of Risk Based
Process Safety (RBPS) in Chapter 3, along with short descriptions for each element.
The book then covers the application of the various RBPS concepts throughout
upstream operations: well construction (both onshore and offshore) in Chapter 4,
onshore production in Chapter 5, offshore production in Chapter 6, engineering
design, construction, and installation in Ch apter 7, and future topics and research
needs in Chapter 8.
As noted earlier, the focus is on process safety (i.e., loss of containment events),
so other major incident hazards (adverse we ather, marine events, structural failure,
transportation incidents) which would require extensive discussion, are not covered
in this concept level book. However, these events can be initiating events for loss of
containment – e.g., the Mumbai High event in Table 1-1. The methods described in
this book can be applied to these other major incident hazards as well. Similarly,
occupational safety is not addressed other than toxicity or fire and explosion that can
affect many people at once.
Liquefied Natural Gas (LNG) can be thought of as upstream or midstream. In
this book, it is covered briefly where the liquefaction occurs offshore in floating
facilities (FLNG units), but not onshore in fu ll scale liquefaction plants as these are
very similar to downstream facilities and thus are already covered in the existing
CCPS library.
A figure showing the topics which are in scope and those that are not in scope
is shown in Figure 1-2. The column topics are addressed in Chapters 4, 5, 6, and 7
as indicated.
1.6 UPSTREAM SAFETY PERFORMANCE
Upstream incidents are tabulated by several organizations. Offshore, individual
regulators collect their own safety data (e .g., BSEE, UK HSE, PSA, etc.). They do
their own reporting, but also share this in formation to the International Regulators
Forum ( https://irfoffshoresafety.com ) allowing for easier comparison between
regions using standardized categories. In the US, upstream onshore activity is less |
8 • Emergency Shutdowns 156
8.7 How the RBPS elements apply
All of the Risk Based Process Safety elements (RBPS) apply when
setting up a process safety and risk management program to manage
the process safety risks effectively. Effective anticipating for and activating shut-downs during emerge ncies is a result of an effective
process safety program. For safe shut-downs at this time—the subject
of this chapter —it is essential that the hazards be understood, the
risks evaluated, and the engineering and administrative controls be identified, designed, implemented, and sustained for the life of the process. Effective proc ess safety and risk management programs are
the subject of considerable guidance today, noting that the knowledge of how to identify, design, implemen t, and sustain the technologies for
these emergency response programs continues to evolve. Additional
guidance for applying and auditing these RBPS elements for an
effective overall process safety and risk management program is
provided other resources [40].
|
474 PROCESS SAFETY FOR ENGINEERS: AN INTRODUCTION
Table A.4. HAZOP Worksheet Node 1 – T-1 WWT Equalization Tank
Node: 1. T-1 WWT Equalization Tank
Drawing Number: P&ID Example
Figure A.5. Risk Matrix
|
10 Human performance and operational competency
10.1 Learning objectives of this Chapter
This Chapter provides an overview of the Human Factors of operational (process
operations, production and maintenance) Competency Management, and explains how competency leads to safer performance. The term ‘operational’ refers to the
skills and knowledge such as understan ding of process hazards and how to
operate and maintain equipment. By the end of this chapter, the reader should be
able to:
• Understand what is meant by the terms competency and Competency
Manage ment.
• Recognize the importance of operational competency in safety critical
tasks, and error prevention.
10.2 What is competency?
Competency is commonly regarded as a set of skills, knowledge, and practical
experience or abilities that enable people to reliably perform tasks efficiently and
safely. This includes routine tasks, and unexpected situations and changes to usual
activities.
Competency is also defined as the abilit y to perform work activities reliably and
consistently, to the required standards. Competency can be measured against
these standards. A term such as “Suitably Qualified and Experienced Person (SQEP)” can be used to indicate that a pers on is competent in their role/in the tasks
they are conducting. This includes rout ine and non-routine tasks; abnormal and
upset; first line emergency response; safe ty-critical maintenance, inspection and
testing activities.
The CCPS “Guidelines for Risk Based Pr ocess Safety” [24] cites “Process
Safety Competency” and “Training and Performance Assurance” as
elements.
The CCPS “Guidelines for Defining Process Safety Competency
Requirements” [50] provides an over view of process safety competency.
This Chapter and Chapters 11, 12 and 13 build on the CCPS guidelines
by providing additional insights and advice on the Human Factors of
competency, learning, and Competen cy Management. These Chapters
focus on operational competency. Human Factors Handbook For Process Plant Operations: Improving Process Safety and System
Performance CCPS.
© 2022 CCPS. Published 2022 The American Institute of Chemical Engineers. |
66 Guidelines for Revalidating a Process Hazard Analysis
• Relying on a prior PHA with inadequate information (e.g.,
incomplete or inaccurate P& IDs or operating procedures)
• Relying on a prior PHA with no node or process section descriptions
• Relying on a prior PHA where the team failed to identify or
document all credible hazards asso ciated with the process, capture
important initiating events, or address all operating modes (e.g.,
startup, shutdown, clean outs, catalyst changes)
• Using a prior PHA where there were fundamental issues with
application of the core methodology. For example, not carrying
consequences to their final conclusion (e.g., stopping at "high
pressure in vessel" rather than considering the possibility of "vessel
rupture" and its subsequent cons equences) or not following loss
scenarios to their conclusion in equipment or processes beyond
the physical boundaries of the PHA being evaluated
• Using a prior PHA where the team risk judgments were suspect. For
example, considering ineffective or unclear safeguards when
evaluating likelihood (e.g., taking credit for operator intervention,
when in reality the event would develop too rapidly for the operator
to respond), or failing to specif ically identify engineering or
administrative controls (e.g., listing “high level switch” rather than
an instrument tag number or “operating procedures” rather than a
procedure number)
• Using a prior PHA that had been documented by exception (i.e.,
only those deviations or scenar ios for which severe consequences
were deemed likely or resulted in a consequence of interest were
documented, such that the reviewer cannot tell whether other
scenarios were overlooked, or if they were considered and
discounted)
• Updating a prior PHA where the previous intention was to not have
any recommendations or a prior PHA with an improbably small
number of recommendations indicating, perhaps, a too-cursory
analysis
• Using a prior PHA with no or limit ed documentation (e.g., there is
no explanation of the methodology used by the prior PHA team)
• Failing to consider future PHA revalidation needs when
documenting and implementing MOCs between revalidation
cycles, resulting in increased effort for the revalidation team and
potential for unexpected results |
Piping and Instrumentation Diagram Development
386
In the process plant world, winterization basically
means implementing specific features in a plant design
and P&ID development to prevent the impact of cold weather on plants in shutdown conditions.
Winterization also can refer to activities to make a
piece of equipment functional even in the harsh condi-tions of winter.
Therefore in a broader sense, winterization is activities
to prevent freezing, frosting, or setting of matter in a process plant in its all operation phases.
The other name of winterization is “Frost prevention”
or “freeze protection. ”
When a plant is shut down, either partially or com-
pletely, after de‐energizing the plant elements, the next step is to drain all the pipes, equipment and containers to make sure there is no trapped liquid in enclosed spaces, and that all of the enclosures are empty. This is to protect the plant during post‐shutdown time to keep the plant safe against anomalies caused by trapped liquids. Trapped water in a plant may freeze and expand, and this expan-sion of frozen water can rupture pipes, equipment or con-tainers. Trapping very heavy oil in plant enclosures will cause it to set and become hard to move. After a long shutdown, this makes the plant’s start‐up very difficult.
For all of these reasons, all the trapped liquid should be
emptied by the plant operator. However, the problem is that each plant may have a few hundred or more drain valves and only a small number of operators. Therefore, draining all the trapped liquid through a few hundred drain valves may take weeks to complete and during this time if the ambient temperature reaches a low level (and the word “winterization” comes from here), it may endanger the plant’s equipment.
There are passive winterization protection and active
winterization protection methods.
The passive winterization protection methods are
generally more inexpensive than active methods. The passive methods could be implemented instead of or in addition to active methods.
The winterization methods are listed in Table 18.7.One passive method of dealing with winterization is
minimizing the exposed area of process items. Such min-imized exposure can be obtained by putting process items indoors, inside buildings or inside sheds/cabinets or by burying underground pipes or containers below the “frost line. ” The frost line is an imaginary surface below the ground surface under which the soil is less affected by the atmospheric temperature. It is assumed that the (wet) soil below the frost line does not freeze in the winter.
For fluid‐in instruments like Bourdon tube pressure
gauges, winterization can be attained by essentially not sending service fluid inside of the instruments. When freezing is an issue in a specific environment and a spe-cific service fluid, specific pressure gauges with filled liquid can be used. In such Bourdon tube pressure gauges the Burdon tube is filled with a non‐freezing
liquid (like g
lycol) and capped with an elastic mem-
brane. The membrane (diaphragm) allows pressure to transmit to the Bourdon tube without allowing the problematic service fluid getting in to the Bourdon tube.
The other good practice regarding dealing with win-
terization is providing sloped piping toward “tolerable” equipment. This technique is known as providing “inter -
nal natural free draining. ” An example of more tolerable items against freezing are tanks.
Elimination of dead legs is important if implementing
the concept of “natural internal drainage. ” Dead legs are Table 18.5 P&ID presen tation of heat conservation insulation for different items.
Pipe Equipment Instrument
H 50
And/or in pipe tag
114–ASL–COS –100–3 8H
EHS–07171–2–B 9W–50H
And/or in equipment call‐outNot common
Table 18.6 Pipes tha
t most likely do not need HC insulation.
●Pipes go to ponds
●Pipes go to coolers (cooling stream of heat exchangers)
●Pipes of “used” cold streams (e.g. CWR)
●Short and large diameter pipes |
178 Human Factors Handbook
15.4 Key learning points from this Chapter
Key learning points include:
• Fatigue can greatly increase the potential for error.
• Causes of fatigue are many, and th ey vary by task and by person.
• Established good practices help managing fatigue.
• Fatigue can be monitored and managed in an operational setting.
|
180 GUIDELINES FOR MANAGING ABNORMAL SITUATIONS
altitude. A combination of lack of feedback from the sidestick and this loss
of protection made it more likely that excessive changes to the flight control
surfaces would occur.
The design of the HMI did not make it easy for the crew to assimilate
the information and form an accurate mental model of what was
happening to the aircraft. Improvements to the HMI design including a
display of angle of attack were recommended in the report.
7.1.7.2 Abnormal Situation Recognition:
Clearly, as soon as the automatic systems disengaged, the aircrew were
aware of an abnormal situation. Howe ver, they were unable to diagnose
what was happening to the aircraft within the available time, which was
a matter of some two minutes. The instruments presented them with
conflicting information: the altitude suddenly appeared to decrease, but
so did the speed, although the me asurements were inconsistent.
Although the display includ ed an artificial horizon, it did not include the
angle of attack. The action to gain height is understandable although in
hindsight, this was the wrong action to take and led to the stall. The stall
indicators sounded repeatedly, but th e PF did not put the nose of the
aircraft down, except very briefly.
Similar situations can occur in the process industries when there are
sudden changes in the weather condit ions. For example, if instrument
air systems are not kept very dry (typically to a dew point of -40 °C
(-40 °F), moisture can freeze in lines or in mechanisms leading to
erroneous readings and stuck valves.
7.1.7.3 Human Factors and Crew Resource Management:
It is typical with incidents of this nature for Human Factors to contribute
to most of the causes. The startle effe ct was a key factor that led to the
large input to the sidestick and the ai rcraft rapidly coming out of a safe
flight envelope. The sudden increase in workload led to a degradation of
the communication between the pilots. The report refers to the surprise
generated by the autopilot disco nnection and the loss of cognitive
control of the situation. The report highlighted that the initial and
refresher training provided did not adequately address this type of
sudden scenario and recommended improvements in this area
including reinforcement of Crew Re source Management (CRM) training
and improved training simulators. |
Ancillary Systems and Additional Considerations
399
is meaningless. The “design pressure” should be men-
tioned “at” a “design temperature” as a pair; e.g. the design pressure of this vessel is 900
KP
ag at design tem-
perature of 80 °C or “900 KP
ag @ 80 °C. ”
For all process items a wise pair of “design pressure @
design temperature” should be selected and requested from the item vendor.
Moreover, this pair should be coincident. This means
that during the operation of a process item a pressure as high as the selected design pressure could happen during the time the temperature is as high as the design temperature.
18.8.1
Decision on “Desig
n Pressure
@ Design Temperature” Pair
See Figure 18.26, which shows pressure and temperature
changes in a piece of equipment during its life time. Pressure and temperature go up and down.
“Bubble 1” shows the absolute highest temperature.
“Bubble 2” shows absolute highest pressure.
From a pure theoretical view point the pair of “design
pressure @ design temperature” should be selected as the pair inside of “bubble 3. ” This is because it represents the highest pressure at the highest temperature. However, we generally and negligently report “bubble 4” as the pair of “design pressure @ design temperature” . “Bubble 4” is obviously not a coincident pair.In the next two sections we discuss decision process
for selecting design pressure and design temperature.
18.8.1.1 Deciding on “Desig n Pressure”
If you remember, in the level system of pressure mentioned in Chapter 5 the design pressure is a level of pressure higher than the HHP (high‐high pressure) and the HP (high pressure) and NP (normal pressure). For the selection of design pressure we can go high, very much higher than the HHP as much as we want, but this increases the cost of process elements. Therefore we need to bring down the design pressure to a level that is inexpensive while safe.
The way we define the “process design” is firstly define
it through a minimalistic approach and the increase is to go higher than (or equal to) the HHP .
What is the minimum safe level of pressure that could
be selected as design pressure?
As it is attempted to keep the pressure on and con-
trolled at the normal pressure (NP) one may say the design pressure could be placed at the normal pressure! However the controllers that try to bring the pressure to the normal pressure are not perfect. Control loops have an “overshoot. ”
In nutshell, “overshoot” is a magnitude of deviation
from the pre‐determined set point of a controller when it tries to keep the parameter at the set point.
As the control technologists generally adjust an over -
shoot of 10% in process plants, the design pressure could be selected as 10% higher than normal pressure as minimum.
After preliminary selection of design pressure as
“NP
+ 10%” we should c
heck to make sure the design
pressure is higher than the HHP and, if it is needed, increase the design pressure to make sure the rest of the pressure levels, HHP and HP , are laid down somewhere in a band between NP and design pressure.
18.8.1.2 Deciding on “Design Temperature”
As was mentioned, the design temperature in the pair of “design pressure @ design temperature” should be a coincident value. However this temperature is generally decided independently of the design pressure. This is the meaning of selecting “bubble 4” in Figure 18.26. What we did basically is selecting the highest absolute pressure and selecting the highest absolute tempera-ture and tied them “nominally” into a “pair. ” We chose this selection and not the more accurate pair of “bubble 3” just because it is easier to do that. It is very difficult to estimate the maximum upset temperature at the upset pressure.
The selected pair may call for stronger, more expensive
equipment but if the additional cost is acceptable, this easier methodology can be used.
Bubble 1Bubble 4Bubble 3Bubble 2
Pressure
Temperature
Life time
Figure 18.26 Pr essure–temperature pair fluctuations in a piece of
equipment. |
PROCESS SAFETY REGULATIONS, CODES, AND STANDARDS 49
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Merriam-Webster, https://www.merriam-webster.com/dictionary . |