Lecture 8 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
This 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 (HAZOP) studies
An effective but less formal type of HAZOP study. The results are highly
dependent on the experience and synergism of the group reviewing the process.
Safety review
is a formal procedure to identify hazards in a chemical process facility
HAZOP Study
when to use HAZOP in new plants
when design is nearly firm and documented
when to use HAZOP in existing plant
review current process or a major redesign is planned
requirements for HAZOP
Technical data
Technical experts
Principles of HAZOP
Concept
Reference/Basis
Method
locations (on P&ID or procedures) at which the process parameters are investigated for deviations. these nodes are points where the process parameters 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 departures from the intention which can be discovered by systematically applying the guide words.
deviations
HAZOP MODEL
guide words
|
causes - deviation - consequences
guide word: no forward when there should be
NONE
guide word: more of any relevant physical property than there should be
MORE OF
guide word: less of any relevant physical property than there should be
LESS OF
guide word: composition of system different from what it should be
PART OF
guide word: more components present in the system that there should be
MORE THAN
guide word: what else can happen apart from normal operation
OTHER THAN
guide word: flow reverses against intended direction
REVERSE
risk is defined mathematically as:
consequences x likelihood
or
severity x frequency
the systematic development of numerical estimates of the expected frequency and consequence of potential accidents associated with a facility or operation based on engineering evaluation and mathematical techniques
QRA
complexity of QRA depends on
objectives of the study
available information
major steps of QRA
- defining potential event sequences and potential incidents
- evaluating the incident consequences
- estimating the potential incident frequencies using event trees and fault trees
- estimating the incident impacts on people, environment, and property
- estimating the risk by combining the impacts and frequencies, and recording the risk.
a semi-quantitative tool for analyzing and assessing risk
LOPA
the protection layers may include
inherently safer concepts
basic process control system
safety instrumented functions
passive devices (dikes/blast walls)
active devices (relief valves)
human intervention
primary purpose of LOPA
determine whether there are sufficient layers of protection against a specific accident scenario
protection layers of LOPA are often depicted as an
onion skin
the major steps of a LOPA study include
- identifying a single consequence
- identifying an accident scenario and cause associated with the consequence
- identifying the initiating event for the scenario and estimating the initiating event frequency
- identifying the protection layers available for this particular consequence and estimating the probability of failure on demand for each protection layer
- combining the initiating event frequency with the probabilities of failure on demand for the independent protection layers to estimate a mitigated consequences frequency for this initiating event
- plotting the consequence versus the consequence frequency to estimate the risk
- evaluating the risk for acceptability (if unacceptable, additional layers of protection are required)
