Chemical Process Safety

PROMIS contains the elements for Process Safety Management and Risk Assessment which are valuable in meeting operator and regulator needs for hazardous facilities. The hazards considered are:  Fire, Explosion and Release of Toxic Substances to the air. The aim is to have a progressive system which ensures that the larger risks (based on potential consequences) receive the most study and as a result control.  

 

 




The aim is to provide simple systems which allow the depth of study to be determined at plant level, thus involving the plant operation staff in understanding the risks and their role in managing them. As the complexity of the risk assessment needs becomes greater, other expert knowledge is needed. This may not be available at plant operations level. There is also a section related to Layer of Protection Analysis (LOPA) and the concept of Inherently Safer Process Design.

The subject of Inherently Safer Process Design is covered in relevant sections of the Chemical Process Safety Pyramid

Within the topic of Chemical Process Safety: The Process Safety management approach uses well respected tools at the assessment stage. These include Hazard and Operability Analysis (HAZOP) to identify hazards, calculation tools to assess severity of potential hazard consequences, Layer of Protection Analysis to assess the degree of protection needed to achieve company or regulator 'tolerable' risk.

The subject of Fire is addressed by the use of the 'Dow Fire and Explosion Index' which is a commonly used method of ranking the fire hazard of a process unit such as a distillation column or reactor. It is useful to provide a screening tool for determining the scale of the problem and deciding if further work is needed to reduce it.  The nature of the index readily provides ways of risk reduction which can be applied through simple process modifications or mitigation of effects.

The subject of Explosion uses a simplified calculation based on the TNO 'Multi Energy' approach to estimating the overpressure caused by vapour cloud explosions in partially confined structures such as process buildings. This allows the user to assess the capability of control rooms and other occupied buildings to survive an explosion event.

For credible Toxic release is addressed by the use of the Dow 'Chemical Exposure Index' which is a simple calculation for the distance travelled by typical releases of toxic vapours. These typical releases are from credible scenarios based on piping leaks, overflows, pressure relief valves etc. The toxic effects are based on Emergency Response Planning Guidelines (ERPGs) listed for many substances by the American Industrial Hygiene Association. Other data such as Immediately Dangerous for Life and Health (IDLH) may also be used in the calculation.  For effects from worst case scenarios, i.e. catastrophic and fast total loss of containment, the United States Environmental Protection Agency (USEPA) Risk Management Program (RMP) calculation method is used. This is also based on ERPGs.

Inherently Safer Process design is an approach where some key concepts such as 'reduce', 'moderate', 'substitute' are applied to reduce the hazard from a process. The suggested tools include the Fire and Explosion and Chemical Exposure Indexes and a guideword application similar to Hazard and Operabilty Analysis. This subject is addressed in the Safer Processes area of the PROMIS Pyramid.

The PROMIS Pyramid for Chemical Process Safety has been created by Richard Gowland. He is a Process Safety Specialist with experience in Engineering, Project Management, Production Management, New Technology introduction, Process Safety and Occupational Safety and Environmental Management in Europe, North America and Asia. His current work includes specialist support for clients in the field of Process Safety and Layer of Protection Analysis.