How to do PHA - Preliminary Hazard Analysis?

The first part should cover theory and is essential for understanding the concept. Continue to the end of the post to see the practical process and usable formats.

Where should the PHA technique be used?

  • It should be used at some point during the conceptual or planning
  • the early improvement of plantselection,
  • 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 where to apply PHA?

A new plant with a new technique. Early identification of the maximum of the dangers can be viable, resulting in powerful cost savings that would otherwise result from major plant redesigns if dangers are observed at a later stage. It can be very beneficial for site selection.

This does not replace the need for hazard assessment; instead, it should be a precursor to further hazard analysis. Items for attention include meticulous preparation of a list of hazards:

  1. Raw materials, intermediates, by-products, finished products;
  2. Plant equipment (high-pressure systems);
  3. Interface between system components (materials, fire systems, etc.);
  4. Environment (earthquake, tsunami, severe temperature, flood); and
  5. Operations (see maintenance and emergency preparedness) Safety system.

The Scope of PHA

  • Hazardous components, 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 controls, and possible alternate approaches
  • Malfunctions, failures, 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 residual gas after use;
  • Lines distributing the gas ‘Ammonia’; and
  • Leakage at some point during receipt of the gas, etc.

The results of those reasons may be:

  • Injury/Fatality to individuals in the plant or nearby areas, and
  • Damage of belongings because of an explosion.

Safety measures/corrective moves supplied to limit impact:

  • Whether less toxic materials may be used;
  • Minimizing storage inventory of combustible materials in the warehouse;
  • Procedure for secure storage of the gas with an enclosure device;
  • Provision of plant warning system;
  • Training for operators on properties and the impact of the material; and
  • Informing neighboring communities of potential hazardous impacts.

The effects of the identification technique may be recorded as Hazard, Causes, Effects, and Preventive Measures.

Ohhhhh that’s was theory …. Bla Bla Bla…

How to do PHA on site?

Let's see a practical example step by step.

Step 1. Establish a PHA team

A typical PHA team may consist of:

  • 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 accidents, 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 similar to Job Safety Analysis and HIRA, or a hybrid version of both. The main difference should be that JSA or HIRA should be done based on the actual scenario, whereas here it will be done based on design and projection assumptions.

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

The risk calculation format may vary in a 3-scale system (Low/Medium/High) or a 5-scale system, but the concept should remain the same to calculate and prioritize risk for preventive actions.

Step 4. Identify the hazards for the system of step 2.

All hazards and possible accidental events must be identified. It is 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:

  1. 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.
  2. Major Failure results in a low level of exposure to personnel or activates facility alarm system.
  3. 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.
  4. Catastrophic failure results in major injury or death of personnel.
  5. Disaster Failure results in a major outbreak which might impact areas beyond the specified boundary and may impact people, employees, and 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:

  1. Very unlikely Once per 1000 years or more seldom
  2. Remote Once per 100 years
  3. Occasional – Once per 10 years
  4. Probable Once per year
  5. Frequent: Once per month or more often

Step 7: Calculate and prioritize the Risk for CAPA

The risk should be established as a combination of a given event/consequence and its severity. This will enable ranking of 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 the post and you may download it for better understanding.

PHA pros and cons

Pros:

  • Helps ensure that the system is 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