1. Hazard identification

2. Introduction
A Hazard and Operability (HAZOP) study is a structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems that may represent risks to personnel or equipment, or prevent efficient operation.
The HAZOP technique was initially developed to analyse chemical process systems, but has later been extended to other types of systems and also to complex operations and to software systems. With respect to maintenance, the HAZOP method could be applied with the following objective:

3. HAZOP objective
Analysis of the technical system in order to find weak points where a maintenance task could reduce the probability of failure, and/or the consequence of a failure
Analysis of the maintenance action (procedure HAZOP) where the objective is to identify critical tasks when executing the maintenance.

4. HAZOP procedure
Divide the system into sections (i.e., reactor, storage)
Choose a study node
Describe the design intent
Select a process parameter
Apply a guide-word
Determine cause(s)
Evaluate consequences/problems
Recommend action: What? When? Who?
Record information
Repeat procedure (from step 2)

5. HAZOP process parameters
Flow Composition pH
Pressure Addition Sequence
Temperature Separation Signal
Mixing Time Start/stop
Stirring Phase Operate
Transfer Speed Maintain
Level Particle size Services
Viscosity Measure Communication
Reaction Control

6. Study node
A study node could be a line, a vessel, a pump, or an operating instruction

7. Guide words Guide word Meaning Example No (not, none)
None of the design intent is achieved
No flow when production is expected
More (more of, higher)
Quantitative increase in a parameter
Higher temperature than designed
Less (less of, lower)
Quantitative decrease in a parameter
Lower pressure than normal
As well as (more than)
An additional activity occurs
Other valves closed at the same time
Part of
Only some of the design intention is achieved
Only part of the system is shut down
Reverse
Logical opposite of the design intention
Back-flow when the system shuts down
Other than (other)
Complete substitution – another activity takes place
Liquids in the gas piping
Early / late
The timing is different from the intention
The valve is opened to late
Before / after
The step (or part of it) is effected out of sequence
The work starts before the high voltage is disconnected
Faster / slower
The step is done/not done with the right timing
Oil is removed faster than the sink can swallow
Where else
Applicable for flows, transfer, sources and destinations
The fluid is emptied in the wrong bottle

9. Example of HAZOP worksheet for the process parameter flowGW
Deviation
Consequences
Causes
Recommend action No
No flow
Too much ammonia in the reactor. Discharge to working area
Valve A fails in closed position
Phosphoric acid depot is empty
Pipe blockage, or pipe fractured
Automatic closure of valve B when no flow from phosphoric depot
Less
Les flow
Too much ammonia in the reactor. Discharge to working area. Investigate the situation!
Valve A partly closed
Pipe partly blocked, or fractured
Automatic closure of valve B when flow is missing or is reduced from phosphoric depot Set-point determined by toxicity and flow limitations
More
More flow
Too much phosphoric acid. No danger in working area