Double Jeopardy & Process Hazard Analysis

Hey guys, hope you are doing well. Today we are discussing "Double Jeopardy" which creates regular dilemma and stirs up arguments during PHA sessions. If you have participated as a team member or facilitated or scribed in a PHA session, you would be aware of the term "Double Jeopardy". When someone declares, “That’s double jeopardy,” during a PHA, they are definitely not fighting a legal case in court where double jeopardy prevents a person from being tried in court twice for the same offense. Instead, they are arguing that because two things have to go wrong to cause a scenario, the likelihood is so low that it is not credible and there is no need to consider the scenario.

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:

Recent incidents in Indian Industry creating turmoil

Yesterday's fire and explosion incident in Yashashvi Rasayan has made me ponder upon the prevention and protection measures taken by the manufacturing plants.

The incident has been said to be in the tank farm area. As per the initial reports, the fire in the tank farm has lead to an explosion of solvent storage tank/ tanks. In multiple images, damaged tanks, hydrogen trolley and multiple other plant units could be seen in the near vicinity of the tank. The other images of the incident are quite disturbing with charred bodies lying on the ground. There is a disturbing video of a charred man asking for help outside the plant that is being circulated in social media. The root cause of the incident still needs to be confirmed by the authorities. 

This incident combined with Vizag Styrene release and Tarapur surfactant factory explosion has put multiple questions in my mind. 

• Do you think that the understanding of Indian industry to process safety has improved? Do you think enough measures are taken in a plant to prevent unsafe acts and unsafe conditions? 

• Do you think that management of your plant or the neighbouring plant is seriously implementing measures and filling gaps identified in audits and PHA studies? 

• Do you think that government authorities are seriously making proactive reviews of the sites? 

• Do you think our laws and regulations related to industries are stringent enough to make the industries realise that they have more to lose in an accident than to gain in the normal operation of the plant? 

In my opinion, some industries have a better understanding of the importance of process safety in their plant and they implement preventive and protective measures as well. But several of them lack resources and knowledge related to process safety and how to prevent unsafe conditions and acts in their plants. They are still limited to hard hat and steel toe shoes safety which is important, but there is so much more to safety.

Many do not understand the importance of a good PHA study and how it can help in preventing and safeguarding against incidents. For example, I have worked with companies representatives who have asked me "why are you taking a scenario of external fire in a tank farm as I have enough fire monitors and hydrant points available in plant to fight such a scenario?" or "Why are you recommending a dump tank for a PSV release as I have high-pressure alarm and interlocks for my vessel?"

Although we have many existing guidelines, laws and regulations. Also, frequent inspections keep on going on in our plants. But it is high time to bend our perspective towards Process Safety along with general safety. It is high time that we understand and focus on topics like chemical reaction and thermal runaway hazards, facility siting, the importance of Management of Change and quality PHAs, risk of Dust Explosion, risk of fire/ explosion due to electrostatic discharges, the importance of QRA (Quantitative Risk Assessment) and LOPA (Layer of Protection Analysis) studies for the major accident hazard scenarios, the importance of Process Safety Management (PSM), etc.

These incidents leave us and our families devastated and in turmoil. We need to learn from these incidents and improve our facilities. At the end of the day, we all should return to our families safe and sound.

Remote HAZOP & LOPA Workshops

Hope you and your families are keeping safe and following the safety guidelines. During these tough times of COVID-19, face-to-face meetings have become a major challenge. To avoid any project delays and missed deadlines, many of my clients have asked me to host HAZOP and LOPA workshops via video conferencing while working from home.

I thought it would be helpful to share some tips for remote facilitation based on my experiences:

Importance of Facility Siting

Is the control room in your facility located close to the tank farm? Is any occupied or functionally significant buildings close to a Maximum Credible Loss Scenario? Is your cylinder storage shed close to the drum filling area?

If you have wondered about this ever, then you should read this article to understand Facility Siting. Some incidents from the past have cleared the importance of facility siting in a plant.

The Flixborough explosion in 1974, where cyclohexane explosion shattered control room windows, collapsed its roof and demolished the brick-constructed main office block. Twenty­ eight people died, and thirty-six were injured in this accident out of which Eighteen of the fatalities were in the control room. Fortunately, over 200 fatalities were averted as the incident took place on Saturday when the main office block was unoccupied.

The Phillips disaster of 1989, where 40000 kg (85000 lbs) of a mixture of ethylene, isobutane, hexene and hydrogen was released and exploded. The second explosion involved BLEVEs of two isobutene storage tanks and the third explosion was the catastrophic failure of the ethylene plant reactor. The explosions killed 23 employees and injured 314.

Should set point for Pressure Relieving Device be equivalent to Design Pressure?

Hope all of you are doing well. Today's topic is focusing on the general practice sometimes followed in industry related to the set point of Pressure Relief Devices of process equipment. Many times during PHA, I have come across a general philosophy of keeping the set point of the reactor's pressure relieving devices equivalent to its design pressure. This might be adequate for a non-reactive system. But the question is, is it adequate for a reactive system?

Here, the reactive system is one where there are hazards due to a chemical reaction, including the possibility of decomposition or polymerization or some side reaction, etc. We know based on normal kinetics that the rate of reaction is directly proportional to the temperature which in turn is proportional to pressure. In simple terms, it is said that the rate of a chemical reaction doubles with every 10 deg C rise in the reaction temperature. Hence it can be said that:

Higher set pressure leads to a correspondingly higher "set" temperature (i.e. the relieving temperature).  This, in turn, leads to a higher rate of reaction which results in higher self-heating or higher temperature rise rate (dT/dt i.e. deg C/min) and a higher pressure generation rate (dP/dt i.e. bar/min). This is very important because for a chemically reactive system the required pressure relief area depends directly on the self-heating and pressure rise rates at the relief conditions.

Risk Ranking:Essence of any Hazard Analysis

Recently, I was giving training on HAZOP and I got a question "Why do you say that our HAZOP is incomplete without risk ranking? We are doing the study since so long and no auditor or authorities have ever questioned us for the same." 

So this question has made me think about the situation Process Safety is facing. We know that oil & gas has developed more than other sectors including FMCG, Pharmaceutical, Chemical (Bulk & Speciality), etc. with far better standards for performing safety studies including PHAs. So, here I am writing this post to share the importance of risk ranking in any hazard analysis technique.