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Process Dynamics and Control > Chapter 10 > Flashcards

Chapter 10 Flashcards

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1
Q

seven common layers of protection

A
  1. process design
  2. basic process control system
  3. alarms and operator intervention
  4. safety instrumented systems
  5. pressure relief devices
  6. containment
  7. emergency response
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2
Q

control systems help

A

detect disturbances
maintain process stability
trigger alarms or shutdowns

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3
Q

mandates that engineers must: “Hold paramount the safety, health, and welfare of the public.” This duty has led to the establishment of professional bodies and standards focused specifically on process safety

A

AIChE Code of Ethics

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4
Q

CCPS was founded in __ after

A

1985 after the Bhopal disaster

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5
Q

how many elements of process safety

A

20

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6
Q
  • Publishes standards for alarm management (ISA-18.2) and safety instrumented systems (ISA-84/IEC 61511).
  • Focuses on reliable control systems and SIS architecture
A

ISA (International Society of Automation)

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7
Q
  • Enforces Process Safety Management (PSM) regulations (29 CFR 1910.119) in the U.S.
  • Mandates hazard assessments, operating procedures, and training.
A

OSHA (Occupational Safety and Health Administration)

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8
Q
  • Oversees Risk Management Plans (RMPs) under the Clean Air Act.
  • Focuses on offsite consequence analysis and prevention of accidental releases.
A

EPA (Environmental Protection Agency)

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9
Q

is the first active layer of protection in industrial processes.

A

Basic Process Control System (BPCS)

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10
Q

It is designed to maintain process variables (like temperature, pressure, level, and flow) within normal operating limits under typical and mildly abnormal conditions

A

Basic Process Control System (BPCS)

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11
Q

a complete BPCS typically includes

A

sensors
transmitters
controllers
actuators
human-machine interface (HMI)

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12
Q

common controller types:

A

distributed control systems (DCS), programmable logic controllers (PLC)

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13
Q

BPCS executes automated control loops

A

maintain setpoints
adjust manipulated variables
respond to measured disturbances

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14
Q

important limitations of BPCS

A

assumes functional components
not designed for emergencies
no fault-tolerance
operator dependency

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15
Q

is a notification to the operator that the process has deviated from its normal operating conditions and requires attention or action

A

alarm

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16
Q

is generated automatically when a measured variable exceeds a specified high or low limit.

A

alarm

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17
Q

are used to denote minor excursions from nominal values, whereas alarm limits indicate larger, more serious excursions.

A

warning limits

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18
Q

overall layers of defense model for process safety

A
  1. BPCS (normal control)
  2. Operator (via alarms)
  3. SIS or ESD (safety shutdown)
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19
Q

are used for critical measurements, with SIS actions based on the median of the three measurements.

A

triply redundant sensors

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20
Q

is an independent, automatic control system designed to take the process to a safe state when predefined hazardous conditions occur.

A

Safety Instrumented System (SIS)

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21
Q

Safety Instrumented System (SIS) serves as a critical layer of protection in the event that:

A

the BPCS fails or
the process moves beyond normal or manageable upset conditions

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22
Q

a typical SIS consists of

A

sensors
logic solver
final elements

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23
Q

component of an SIS that detect unsafe conditions

A

sensor

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24
Q

components of an SIS that processes input and determines if a shutdown is needed

A

logic solver

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25
components of an SIS that execute the action
final elements
26
is a control logic mechanism that enforces a specific action when a predefined process condition is met
interlock
27
Its purpose is to prevent unsafe process operations before dangerous situations arise
interlock
28
common interlock scenarios
low-level interlock high-temperature interlock sequential interlock
29
interlocks help enforce
safe setup, shutdown, bypass conditions
30
is a dedicated safety layer designed to bring the plant to a safe state in the event of major equipment failures, fire, toxic release, or any uncontrollable hazardous event
emergency shutdown system (ESD)
31
ESD activation triggers:
* high-pressure or high-temperature excursions * fire detection in equipment or cable trays * critical valve or pump failure * operator-initiated emergency stop (manual trip)
32
interlocks are implemented in
programmable logic controllers (PLC) or DCS logic blocks
33
common alarm system failures
alarm floods chattering alarms nuisance alarms duplicate and conflicting alarms
34
common alarm system failure where * Dozens or hundreds of alarms activate in seconds. * Overwhelms operator → missed or delayed response.
alarm floods
35
common alarm system failures where: * Rapid toggling (on/off) due to tight limits or signal noise
chattering alarms
36
common alarm system failure where: * Trigger frequently with no real action needed. * Lead to alarm desensitization.
nuisance alarms
37
common alarm system failure where: * Multiple alarms for the same event. * Alarms triggering out of sequence or contradicting each other.
duplicate and conflicting alarms
38
early alarm systems
simple light panels and horns required manual acknowledgement by the operator limited number of variables typically <100
39
modern alarm systems
use of distributed control systems (DCS) thousands of variables can trigger alarms lack or prioritization or filtering leads to alarm floods and operator confusion
40
standard provides a comprehensive lifecycle model for alarm system management
ISA-18.2
41
number of best-practice guidelines for alarm systems
11
42
alarm systems must be:
rationalized prioritized auditable
43
is the process of evaluating every alarm in the system
alarm rationalization
44
alarm rationalization ensure that it is
justified, actionable, appropriate
45
is not about removing alarms randomly—it's about keeping the right ones with the right configuration.
rationalization
46
unrationalized alarm systems often suffer from
* Alarm floods * Redundancies * Missing critical alerts * Operator desensitization (alarm fatigue)
47
a simple calculation can identify a common type of sensor malfunction or fault
dead (or frozen) sensor
48
is any unplanned deviation from the normal operating state of a process
abnormal event
49
the early detection of abnormal conditions, an activity referred to as
abnormal event detection
50
abnormal events can lead to
* Reduced product quality * Equipment damage * Safety risks or environmental releases
51
involves analyzing real-time signals from individual sensors
sensor-based fault detection
52
sensor-based fault detection detect signs of
sensor failure incorrect measurements abnormal process behavior
53
It is a first line of defense in identifying localized issues before they propagate into broader system failures
sensor-based fault detection
54
common sensor fault types
spike drift bias/offset stuck sensor noise
55
techniques used in detection
1. threshold monitoring 2. rate-of-change monitoring 3. redundant sensor comparison 4. signal consistency checks
56
simple limit checking; effective for clear out-of-range faults
threshold monitoring
57
detects abrupt changes or spikes by checking how fast a variable changes
rate-of-change monitoring
58
install two or more sensors for the same variable; fault is flagged if signals deviate significantly
redundant sensor comparison
59
use engineering knowledge to verify if a value makes sense in the current operating context
signal consistency checks
60
compare measured process values to predictions generated by a mathematical model of the process.
model-based methods
61
is the difference between what is measured and what the model predicts
residual
62
use rules, heuristics, or data-driven patterns rather than relying on physical models (as in model-based methods)
knowledge-based methods
63
Knowledge-based methods use rules, heuristics, or data-driven patterns derived from:
* Human expertise * Historical process data * Event analysis * Diagnostic logic
64
they infer abnormal behavior by evaluating whether the current process state matches known fault patterns or rules
knowledge-based methods
65
types of knowledge-based approaches
1. rule-based systems 2. fault trees and diagnostic graphs 3. data-driven pattern recognition 4. machine learning and AI-based methods
66
the probability that the component does not fail during the interval
reliability
67
These use logic relationships to map symptoms to root causes
fault trees and diagnostic graphs
68
two types of analyses based on logic diagrams:
fault tree analysis event tree analysis
69
display all the component failures that can lead to a very serious situation, such as an accident or an explosion, and the subsequent chain of events.
fault trees
70
similar to fault trees but focus on a single initiating event, such as a component failure, and then evaluate the consequences, classified according to how serious they are.
event trees
71
bottom-up approach; its starting point is a single cause, rather than a single outcome
ETA
72
top-down approach that generates a tree of causal relations, starting with the specified top event and working backward
FTA
73
These systems apply IF–THEN logic rules developed by domain experts
rule-based systems
74
These techniques rely on historical process data to establish patterns of normal and abnormal operation.
data-driven pattern recognition
75
popular methods of data-driven pattern recognition
principal component analysis statistical process control clustering algorithms
76
popular method of data-driven pattern recognition that projects multivariate process data into a low-dimensional space to identify deviations
principal component analysisc
77
popular method of data-driven pattern recognition that control charts for variance, residuals, etc.
statistical process control
78
popular method of data-driven pattern recognition that classify process states into known categories (normal, alarm, shutdown)
clustering algorithms
79
modern implementations of machine learning and AI-based methods
supervised learning unsupervised learning fuzzy logic
80
is a quantitative or semiquantitative measure of the likelihood that a hazardous event will occur and the severity of its impact
risk
81
types of risk assessment
qualitative semiquantitative quantitative
82
type of risk assessment that is * Based on expert judgment and experience. * Uses categories like “low,” “medium,” “high” for risk.
qualitative
83
type of risk assessment that * Uses numerical scoring for probability and consequence. * Often plotted on risk matrices
semiquantitative
84
type of risk assessment that * Uses exact failure rates and event trees/fault trees. * Provides precise risk values (e.g., fatalities/year).
quantitative
85
is the probability that a component or system performs its intended function without failure over a specified time period
reliability
86
the failure rate over a component's life typically follows three stages:
1. infant mortality 2. useful life 3. wear-out
87
early failures due to defects or poor manufacturing
infant mortality
88
constant failure rate
useful life
89
aging and degradation increase failure rate
wear-out
90
is a top-down logical diagram that identifies how a specific undesirable event (called the top event) can occur by tracing combinations of lower-level failures.
fault tree analysis (FTA)
91

Process Dynamics and Control (9 decks)

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