HAZOP (Hazard and Operability) studies have been done for years for many plants and facilities; however, there are still many managers and engineers in many different industrial and manufacturing sectors who are not familiar with HAZOP and its safety benefits. Sometimes engineers even panic if a HAZOP study is asked or if invited to a HAZOP session. This article discusses HAZOP and its effectiveness and usefulness for plants and facilities.
A HAZOP is used to identify major hazards or operability issues related to the design, installation, and operation of industrial and manufacturing plants. Major hazards include the release of hazardous materials or energy. This is closely related to risk assessments and safety verifications of facilities. The focus of the study is to address incidents, which may impact public health and safety, worker safety, economic loss, the environment, and the plant’s reputation.
In a HAZOP study, an industrial or manufacturing facility is broken down into “nodes”. Each node will be examined under the direction of several guidewords such as high pressure, low pressure, low flow, high flow, no flow, reverse flow, etc. Some guidewords will become specific to each system or team. For example, operation team, commissioning team etc., each has its guidewords.
One of the primary purposes of HAZOP is the identification of scenarios that would lead to the release of hazardous materials into the atmosphere, thus exposing workers and people living surrounding a plant to danger. To make this determination, it is always necessary to identify, as exactly as possible, all consequences of any credible causes of a hazard.
Ensuring that the HAZOP meeting covers the required scope of the HAZOP study is an important task. Too often, HAZOP studies failed to cover whole the intended scope or sometimes they exceeded defined battery limits. A clear scope definition is important to HAZOP.
Another important element that is essential for a successful HAZOP study is that “all possible modes” of operation, start-up and shutdown for the equipment, machinery, package, etc., should be considered. Machinery, package or facility has different normal, part-load and emergency modes of operation; all modes should be considered, and proper guidewords should be applied for each mode of operation. Care should be taken to identify less obvious modes, particularly those associated with different shut-down situations, such as normal shutdown cases and different emergency shut-down situations in various circumstances, and the subsequent start-up and their combinations.
The scope of a HAZOP study should ensure that all possible deviations from design intent and normal operation are not only identified within the immediate scope of the HAZOP study but are also identified concerning upstream and downstream systems.
In large machinery, packages or facilities, the HAZOP study is usually conducted in stages. There is a potential for incomplete follow-through of problems, issues and consequences and for things to slip between the individual boundaries.
The follow-up of recommendations arising from a HAZOP study is a key part of the HAZOP. The validity and effectiveness of the HAZOP study are seriously compromised if recommendations are not followed through.
Relative priorities of all actions should be determined. After each recommendation has been reviewed, the resolution of each recommendation should be recorded in a tracking document and kept on file. Recommendations can include design, operating, or maintenance changes that reduce or eliminate deviations.
In batch operation, production or manufacturing occurs in time-sequential steps in discrete batches. For example, a batch of feedstock or raw materials is fed or charged into a unit, then the industrial or manufacturing process takes place and the products, and any other outputs are removed. Such a batch production may be repeated again and again with new batches. Batch operation is commonly used in smaller-scale plants and facilities. Machinery and facilities involved in batch-operated units require special attention. There have been many risks and dangers involved in any batch process. All safety and risks on each step in a batch process and how each step can affect whole the process should carefully be studied and verified.
SAFETY VS. OPERABILITY
“Hazard” is any item or operation that could cause a catastrophic release of toxic or dangerous materials, release of uncontrolled energy or any action that could result in injury to personnel and people. The identification of hazards is the main focus of a HAZOP. However, a HAZOP is also expected to identify “operability problems” which are any operation inside the HAZOP scope that would cause a shutdown, particularly those that could lead to a violation of environmental, health or safety regulations or negatively impact profitability.