Process Safety Management in the Chemical Engineering
Process Safety management is a subject that we feel is a vital part of the education of chemical engineers.This article will discuss Process Safety Management, why we feel it is essential, the various aspects of hazard identification and prevention and the responsibilities of our profession in this respect. There is a broader pedagogical issue here that we will deal with as well. The field of engineering practice is changing rapidly driven by many factors such as globalization, the breakdown of old hierarchical structures of management as a result of enormous increases in collaboration, and the rapid change is the skills and knowledge required of our graduating engineers. There is an impending crisis in North America where many of the senior managers, scientists and engineers are soon to retire. This will mean the loss of irreplaceable knowledge unless there is some way to effectively pass it on to the next generation of individuals responsible for keeping economy viable.
The modern civilization is totally dependent on the process industries whether they are Oil and Gas,Chemical (which of course includes the bio option),Pharmaceuticals and so on. By the very nature of these industries one often must deal will significant potential hazard such as fire and explosion, toxic release and many other similar situations? The process industries have by and large made a significant effort to mitigate these risks, however they still will exist because of the various materials and processes involved. There are many instances where disasters occurred because of poor design, unsafe operating conditions and errors in judgement
The Flixborough works of Nypro produced caprolactam a monomer for nylon. One of the critical steps was the oxidation of cyclohexane to cyclohexanol in a series of six catalytic reactors in the presence of air. It was discovered that one of the reactors had a small crack resulting in an unplanned shutdown. This reactor was removed from service and a temporary pipe section was fabricated in the machine shop to replace the cracked reactor. Anecdotal evidence states that the pipe was designed with a piece of chalk on the floor of the maintenance shop. This temporary section was not adequately supported and upon pressurization it failed and released a large cloud of cyclohexane vapour. An unknown source of ignition caused this cloud to explode resulting in the death of 28 people and the injury of some 36 others. There was significant damage in the adjacent village.
An insecticide plant in India suffered an accidental release of methyl isocyanate. This plant jointly owned by Union Carbide and local investors was essentially shut down at the time because of a labour dispute. Because the plant had been designed to receive shipments of MIC from another unit where it was produced there was a fairly large storage tank for the material. MIC will react slowly and exothermically with water and the MIC will boil if not adequately cooled. Somehow water was injected into this tank, some believe it was sabotage by a disgruntled operator; however the result was that the tank boiled over. The vapours popped the pressure relief valve and under normal conditions would have been diverted safely into a scrubber and flare system. Unfortunately this equipment was out of service and an estimate of some 25 tons of extremely toxic vapour escaped, killing some 2,000 people living in the shanty village surrounding the plant and injuring some 20,000 others.
Piper Alpha was an oil rig in the North Sea that was producing crude oil. It had been modified to handle natural gas as well. There were two large pumps both with relief valves on their discharge. One of these pumps had been taken off line because of a problem with the relief valve. The valve had been removed and a blind flange (a round sheet of steel) had been used to block off the line from this pump. Normal obligatory maintenance procedure requires that a ticket must be filed with the operating personnel. Unfortunately there was some mix-up and the ticket was never properly processed. Upon start up of the pump with the working relief valve it developed problems and the operating crew being unaware that the relief valve on the other pump had been replaced with a steel blind flange (the ticket had been misplaced or lost), shut down the pump and attempted to start up the other. The net effect of this was that the blind flange was unable to withstand the pressure and blew off the line discharging a cloud of natural gas, which ignited. This could have been dealt with as there was a water spray system that pumped seawater to several spray heads. Unfortunately there had been some maintenance work carried out near the intake to the water pumps and they were not available. Not to belabour the issue there were other unfortunate occurrences related to the fact that Piper Alpha was on a crude oil grid. The fire was soon out of control and so fierce that rescue craft were unable to approach the rig. A few of the men on the rig saved themselves by leaping several stories into the sea which at this point was covered with burning oil. The rest of the men perished in a structure that was supposed to be a safe haven but in fact became an oven. The rig was totally destroyed. One could bring up many other tragic events but the past three should serve to point out several fundamental aspects of Process Safety Management. Safety begins at the design stage, and is an integral part of operations and maintenance procedures. While most of these principles have been recognized far many years in the industry, it is now called Green Engineering.
Process Design The primary objective of any process design is to design a unit that is inherently safe. In any chemical process it is vital that one is aware of the properties of all the materials and mixtures thereof that are involved in the system. Although there are many situations where the presence of a toxic material is unavoidable, every effort should be made to find alternate chemistry or alternate processes to minimize any hazard. In both the Flixborough situation as well as Bhopal, should there have been a much smaller inventory of for example the cyclohexane in the Flixborough case and definitely the amount of MIC on hand at Bhopal the extent of damage would have been much less. In the later situation redesign of similar insecticide units basically practice “Just in Time” where the intermediate of a very dangerous material such as MIC is kept as small as practically possible. The process selection is very important as well. High operating temperatures and pressures and corrosive environments increase the risk associated with the unit. The introduction of advanced catalysts often permits operating at reduced pressure and temperature without sacrificing yield and selectivity. Selection of the appropriate materials of construction can be very important as corrosion can lead to catastrophic equipment failure.
Before any process design is approved for construction it should be subjected to a rigorous Process Hazards Analysis (PHA) such as a fault tree analysis or a Hazards and Operability Studies (HAZOP) These are a rigorous review of the process design in order to anticipate wherever possible potential risks and to do whatever is possible to minimize these.
Process Control systems are very important as well since in most units these systems are the main tool for operating the plant in a safe manner. It is not possible to go into much detail at this point but appropriate control strategies are essential to safe operation. The primary philosophy of instrumentation should be that all systems are essentially “fail safe”. One of the most important and often overlooked aspects of Process Design is to have the process operators who will have responsible for operation involved thoroughly and often as the design and PHAs progresses. Safety training for all operating personnel, operators and technical staff is imperative. Most large organizations such as the major Oil and Gas companies as well as the major Chemical companies are quite diligent in this respect. This is not only concern for their personnel but the surrounding community as well and there is always the aspect of potential large financial losses resulting from major incidents. Union Carbide never recovered from the Bhopal incident. A recent disaster at Texas City where a distillation column was somehow allowed to fill with liquid which overflowed , resulting in an explosion and fire with significant loss of life. There were criminal charges brought against those who were believed responsible this and presumably jail time was the result. Maintenance procedures are critical as well; the Flixborough and Piper Alpha incidents are examples of complete breakdown in both cases. It is really quite remarkable that a critical piece of equipment was “designed” by a chalk drawing on the floor of a maintenance shop, and the fact that the maintenance “Ticket” got misplaced on the Piper Alpha resulted in the death of many individuals.
Having briefly reviewed some of the aspects of Process Safety Management, we come to the issue of where this can be dealt with in the Curriculum and for that matter should it even be part of a Chemical Engineering education.
The core body of knowledge expected of today’s engineering graduate seems to continue to expand. In addition to the fundamentals of math, chemistry and physics today’s graduate has to be aware of process simulation and computer mathematical tools. Depending on whatever industry one is familiar with this list can be changed and expanded. In most Universities there is a four year programme. It is an enormous challenge to fit all this material into those four years. There is no question that a five year undergraduate degree would be a desirable option. This is certainly not a new idea however who is to pay for it. Parents and students would not be interested in this with the possible exception of the small numbers who choose to go on into grad school. It is an open question whether potential employers would be interested. We suspect that most really wouldn’t be all that interested. Our TEAM program each year deals with some 20 Industrial Organizations. Almost without exception they tell us that provided a potential employee has a degree from an accredited University they assume that there fundamentals are sound. This does not mean that the student’s marks aren’t important, they certainly are. What seems to be the general response from potential employers is that the fundamentals are only one aspect of what they are looking for. The other aspects are usually categorized by that dreadful term “Soft Skills”, which include teamwork, ability to communicate both by written word and orally, but most important, to be a quick learner who can contribute fully to the enterprise. The other aspect of the Engineering Profession today, that we as educators must recognize, is that change is rapid and all embracing.
Process Safety Management is a vitally important aspect of Chemical Engineering whether involved in design, operation or maintenance. Students have to make them fully aware of the importance of this issue. The practice of engineering is changing very rapidly and we as educators are being challenged to adapt to this. The problems we face in order to effectively deliver a programme of Process Safety Management is the less awareness of the subjects among the students.
Article by: Barrie Jackson Associate Professor of Chemical Engineering Queen’s University, Kingston Ontario Canada