HAZARDS IDENTIFICATION METHODS Flashcards
This is a list of items and possible problems in the process that
must be checked
Process hazards checklists
This can be as simple as an inventory of hazardous materials, or it can be as
detailed as the Dow indexes
Hazards surveys
are a formal rating system, much like an
income tax form, that provide penalties for hazards and credits for safety equipment and
procedures.
Dow Indexes
approach allows the mind to go free in a
controlled environment. Various events are suggested for a specific piece of equipment with
the participants determining whether and how the event could occur and whether the event
creates any form of risk
Hazards and Operability Studies
An effective but less formal type of HAZOP study
Safety review
The results are highly
dependent on the experience and synergism of the group reviewing the process
Safety review
A formal procedure to identify hazards in a chemical process facility
HAZOP Study
It is a brainstorming, multidisciplinary approach
HAZOP Study
It is structured using guide words
HAZOP Study
It is problem-identifying and cost-effective
HAZOP Study
Use HAZOP when design is nearly firm and documented
New Plants
Use HAZOP when reviewing current process or a major redesign is planned
Existing plant
Requirements of HAZOP Study
Technical Data and
Technical Experts (HAZOP Team)
Detailed information on the process must be available. including up-to-date PFDs and P&IDs, detailed equipment specs, materials of construction and mass and energy balances before the HAZOP Study is started
Technical data
T/F: Detailed information on the process must be available. including up-to-date PFDs and P&IDs, detailed equipment specs, materials of construction and mass and energy balances after the HAZOP Study is started
F
Requires considerable knowledge of the process, instrumentation, and operation,
Technical experts (HAZOP Team)
Principles of HAZOP
Concept
Reference/Basis
Method
Systems work well when operating under design conditions; problems arise when deviations from design conditions occur
Concept
This is a word model, a PFD, or a P&ID
Reference/Basis
Use guide words to question every part of process to discover what deviations from the intention of design can occu and what are the causes and consequences
METHOD
The locations (on P&ID) at which process parameters are investigated for deviations
Study nodes
These are the points where the process parameters (P,T,F) have an identified design intent
Study nodes
Defines how the plant is expected to operate in the absence of deviations at the study nodes
Intention
These are the departures from the intention which can be discovered by systematically applying guide words
DEVIATIONS
Design intent may cover?
Process conditions
Activites
Substances
Time
Place
HAZOP Model
Deviation is applied Guide words in order to assess the Causes and Consequences
Consequences are ?
Trivial
Important
Catastrophic
Negation of Intention
No, None
Quantitative increase
More of
Quantitative decrease
Less of
Qualitative increase
As well as (More than)
Qualitative decrease
Part of
Logical opposite of intention
Reverse
Complete substitution
Other than
No flow possible causes, consequences, and actions required?
Pump Fail, Line Blockage, Operator stops the pump
System Overheated
Shutdown System
More Flow possible causes, consequences, and actions required?
Excessive pump speed (Control system)
Over-cooled product (incomplete Rxn)
Product Unacceptable: Dump
Two risk assessment types
QRA & LOPA
Risk is defined mathematically as?
Consequences x Likelihood
Severity x Frequency
Flow of Risk Assessment
Hazard Idenification
Consequences and Frequency Analysis
Risk Evaluation
Risk Assessment
Systematic development of the numerical estimate of the expected frequency and consequence of the potential accidents associated with a facility or operation based on engineering evaluation and mathematical techniques
Quantitative Risk Assessment
Complexity of QRA depends on?
Objectives of the study
Available info
These will result when QRAs are used at the beginning of the project (conceptual and design phase) and are maintained throughout the facility’s life cycle
Maximum benefits
Used to evaluate potential risks when qualitative methods cannot provide an adequate understanding of the risk
QRA
Major Steps of a QRA Study
- Define the potential event sequences and potential incidents
- Evaluate the incident consequences
- Estimate potential incident frequencies using event trees and Fault trees
- Estimate the incident impacts on P, E and P
- Estimate the risk by combining the impact and frequencies
A semi-quantitative tool for analyzing and assessing risk
LOPA
Protection layers may include inherently safer concepts like?
Basic PCS
SIF
Passive devices (Dikes and Blast walls)
Active Devices (Relief valves)
Human Intervention
Here, the consequences and effects are approximated by the categories, the frequencies are estimated, and the effectiveness of the protection layers are approximated
LOPA
In LOPA these are selected to provide conservative results
Approximate values and
Categories
Primary purpose of LOPA is to?
Determine whether there are sufficient layers of protection against a specific accident scenario
Protection layers are often depicted as?
Onion skin
T/F: Each protection layer in LOPA is dependent in terms of operation
F
T/F: The failure of one layer does not affect the next in LOPA?
T
Major steps in LOPA Study
- Identify a single consequence
- Identify accident scenarion and cause associated with the consequence
- Identify the initiating event for the scenario and estimate the initiating event frequency
- Identify the layers of protection for this specific consequence and estimate probability of failure on demend for each protection layer
- Combine initiating event frequency with the probabilities of failure to estimate mitigated consequence frequency for this initiating event
- Plot the consequence vs consequence frequency to estimate risk
- Evaluate risk (and add layers if required)
