Strategy to define risk reduction measures in PHA

Hope you and your families are keeping safe from COVID. I have been away from writing for some time now as I took up a new professional role in July and had a lot going on. But one of my new year resolutions was to again start writing the blog and share valuable information with you all. Today I am writing about a strategy one can opt for while providing recommendations in a PHA in order to ensure the provision of effective safeguards.

Process Hazard Analysis (PHA) identifies and evaluates hazardous scenarios forming an initiating event - consequence of interest pair. Evaluating a hazardous scenario helps to determine the adequacy of safeguards for a scenario and to establish requirements for improvement of existing safeguards or installation of new safeguards. 

The need for risk reduction measures is defined based on risk assessment usually utilizing predefined risk matrices. Risk reduction measures fall in either of the two categories “Preventative” and “Mitigative”. Preventative is a category that focuses on preventing the hazard while Mitigative is a category that focuses on minimizing the consequences of an event. 

In order to define risk reduction measures, one of the useful strategies is to employ the hierarchy of controls:

As we move down the hierarchy, the reliability of the risk control measure generally decreases. The topmost in the hierarchy is Inherent Safety, which focuses on eliminating or reducing the process hazards in a way that is permanent and inseparable from the process. Inherent safety is of two orders where the first order Inherent safety is focused on avoiding and eliminating the hazard such as replacing a toxic solvent with water as a solvent. However second-order focuses on reducing the severity of a hazard or likelihood of a release such as redesigning high pressure & temperature process to operate at ambient pressure & temperature.

Segregation & Separation is the next level in hierarchy where segregation means providing a physical barrier between hazards and sensitive receptors/ areas to be protected. Separation involves locating hazards far away from sensitive receptors/ areas.

Next in the hierarchy are Engineering Safeguards which include Passive and Active engineering safeguards. Passive engineering safeguards are the ones that do not need physical activation to perform the intended function such as a dike wall around an above-ground storage tank. Active engineering safeguards require physical actuation whether in response to a change in a process parameter or operator signal or by a control system such as a deluge system. 

Procedural safeguards are based on procedures and involve administrative controls such as the work permit system. Since they are dependent on people, they tend to be less reliable as compared to engineered safeguards. 

Personal protective equipment (PPE) is the next one as they protect people after a hazard has been realized. PPEs are not considered too reliable, as correct usage is people dependent.

Last in the hierarchy is emergency response, where one depends on the first responders after all other safeguards have failed in response to an incident.

Since every risk reduction measure is different in where it stands in the hierarchy of controls, hence it is important to provide risk reduction measures based on the process risk. Higher consequence events should be provided with safeguards higher in the hierarchy.

As a process safety professional, I always advise having at least one effective preventative safeguard apart from mitigative safeguards. It goes without saying that any risk reduction measure being which is being suggested should be reviewed to ensure no introduction of any new hazard.

Hope this helps you all in understanding the strategy for providing recommendations in a PHA study.