How to do PHA - Preliminary Hazard Analysis?
Where the PHA technique should be used?
- It should be used at some point of the Conceptual or planning,
- the early improvement of plant selection,
- the early layout section of a plant.
The technique should be meant to be used simplest within side the initial section of plant improvement for instances wherein revel in presents very little perception into capability protection problems,
Example of wherein to apply PHA?
A new plant with a new technique. Early identification of a maximum of the dangers can be viable ensuing in a powerful saving in value that would in any other case result from foremost plant redesigns if dangers are observed at a later stage. It may be very beneficial for ‘web website online selection’. It does now no longer forestall the want for also danger assessment; instead, it should be a precursor to the next hazard analysis. Items for attention include meticulous preparation of a listing of hazards:
- Raw materials, intermediates, by-products, very last products;
- Plant equipment (high-pressure systems);
- Interface amongst system additives (material, fire etc);
- Environment (earthquake, tsunami, severe temperature, flood); and
- Operations (take a look at maintenance and emergency preparedness) Safety system.
The Scope of PHA:
- Hazardous components or materials or substances.
- Safety or OHSE interfaces between system elements
- Environmental Impact including operating environments
- Operation, test, maintenance, built, diagnostics, and emergency preparedness
- Facilities, property of installed equipment, support equipment, administrative control and training
- Safety-related equipment, safeguards, engineering control and possible alternate approaches
- Malfunctions, maloperation and damage to the system, subsystems, or software
Example of PHA:
Toxic gas ‘Ammonia’ is one of the additives used inside the procedure; so we need to list out below mentioned points to identify the probability of accidents and severity of risk.
Reasons for the dangers:
- The dangers because of storing the gas;
- Hazards from the extra gas after the use;
- Lines distributing the gas ‘Ammonia’; and
- Leakage at some point of the receipt of the gas etc.
The results of those reasons may be:
- Injury/Fatality to individuals in the plant or close by areas, and
- Damage of belongings because of an explosion.
Safety measures/corrective moves supplied to limit impact:
- Whether much less poisonous fabric may be used;
- Minimizing the stock for the garage of the fabric;
- Procedure for secure storage of the gas with an enclosure device;
- Provision of plant caution system;
- Training for operators on properties, the impact of fabric; and
- Informing neighboring localities approximately the poisonous impact.
The effects of the identification technique may be recorded as Hazard Causes Effects Preventive Measures.
How to do PHA in the site?
Let's See Practical example step by step.
Step 1. Establish a PHA team
- A team leader with competence and experience in the method to be used
- A secretary who will report the results
Team members (2-6 persons) who can provide the necessary knowledge and experience on the system being analyzed
The team members who should participate will depend on the system and objectives of the analysis. Some team members may participate only in related parts of the analysis.
Step 2.Define and describe the system to be analyzed
- System boundaries (which parts should be included and which should not)
- System description with detailed layout drawings, process flow diagrams, block details and so on
- Use and storage of energy and hazardous materials in the system
- Operational and environmental conditions to be considered
- Systems for Identification, prioritization and control of hazards and accident, emergency systems, and corrective & preventive actions.
Step 3.Collect risk information in the prescribed format
The results of the PHA are generally reported by a PHA worksheet (or, a computer software also used). A typical PHA format is shown below. Some analyses may require other columns, but these are the most common.
The format should be like Job Safety Analysis and HIRA or we may say its hybrid version of both. The main difference should be that JSA or HIRA should be done based on the actual scenario and here we will do it based on our primary design and projection.
Site Name | Date | ||
Task Identified | |||
Team Member | |||
Sr. | Hazard | Probable accident event (What, Where, When etc) | Probable cause | Preventive action | Probability (P) | Severity (S) | Risk (P x S) | Remark |
Step 4. Identify the hazards for the system of step 2
All hazards and possible accidental events must be identified. It should be important to consider all parts of the system, operational modes, maintenance operations, safety systems, and so on. All findings shall be recorded. No hazards are too insignificant to be recorded. Murthy’s law must be borne in mind: “If something can go wrong, sooner or later it will”.
To get a complete survey of all possible hazards it may be beneficial to use a hazard checklist. Several checklists are available in the literature.
Step 5. Severity calculation of Hazard identified in step 4
An accidental event may lead to a wide range of consequences, ranging from negligible to catastrophic. for example a fire should be extinguished fast and give minor consequences, or lead to a catastrophe. In most applications, the severity of an consequence of an accident to be assessed. In other applications, we have to consider several possible consequences, including the worst foreseeable consequence derived by ETA or FTA of the accidental event.
The severity of an event may be classified into rather broad classes. An example of such a classification is:
- Minor Failure results in minor system damage but does not cause injury to personnel, allow any kind of exposure to operational or service personnel or allow any release of chemicals into the environment.
- Major Failure results in a low level of exposure to personnel or activates facility alarm system.
- Critical Failure results in minor injury to personnel, personnel exposure to harmful chemicals or radiation, or fire or a release of chemical to the environment.
- Catastrophic Failure results in major injury or death of personnel.
- Disaster Failure results in the major outbreak which might impact out of the boundary specified and may impact people, employee, the environment at a larger scale
Step 6.Probability/ Frequency calculation of Hazard identified in step 4
The risk related to an accidental event should be a function of the frequency of the event and the severity of its potential consequences. To determine the risk, we have to estimate the frequency and severity of each accidental event.
The Probability/ Frequency of events may be classified into rather broad classes. An example of such a classification is:
- Very unlikely Once per 1000 years or more seldom
- Remote Once per 100 years
- Occasional Once per 10 years
- Probable Once per year
- Frequent Once per month or more often
Step 7.Calculate and prioritize the Risk for CAPA:
The risk to be established as a combination of a given event/consequence and the severity of the same event/consequence. This will enable g of the events/consequences in a risk matrix.
Sort the task by risk score to prioritize them and decide Corrective Action and Prevention Action (CAPA). Make necessary changes in design, material, process and implement safety measures in the designing stage.
Practical .xls File is attached below via link and you may download it for better understanding.
PHA pros and cons:
Pros:
- Helps ensure that the system should be safe
- Modifications are less expensive and easier to implement in the earlier stages of design
- Decreases design time by reducing the number of surprises
Cons:
- Hazards must be foreseen by the analysts
- The effects of interactions between hazards are not easily recognized
