BACKGROUND

Process Safety Management occupies a key role in the entire management of safety in large scale chemical plants. By itself, however, process safety management may not be able to achieve zero or target hazard rates – it is only through a combination of process safety management, strong operating and maintenance practices, thorough training and development of personnel and other aspects that requisite standards could be achieved.

Process Safety is related to mainly safety aspects covered during design that are related to the process in question – these include fundamental concepts such as ensuring handling and use of “safe” chemicals, “moderate” operating conditions, minimum inventory etc. As well as design mitigation measures such as HIPS (High Integrated Protective Systems), Shut Down Loops, DCS and PLC based operations and other features provided for process safety.

Process safety does not end with the design itself but continues through the form of process safety reviews during the course of the project. The process safety management is a powerful management tool and covers a wide host of areas. The elements covered under safety management have been broadened over the years and presently includes areas such as:

  • Organization Structure
  • Management Personnel and Systems
  • Training for operations and emergencies
  • Safety Assessment
  • Design Procedures
  • Procedures for operations, maintenance, modifications and emergencies
  • Contractor Safety Management
  • Involvement o operators and contractors in safety
  • Accident and Incident Reporting, Investigation and Follow up
  • Monitoring and auditing of the operation of the system
  • Systematic reappraisal of the system in light of experience.

It is well recognized that process safety management of highly hazardous installations requires a tremendous focus on process safety the main elements of which include as following:

1. Hazard Identification
2. Process
3. Hazard Analysis
4. Risk Assessment
5. Emergency planning for identified risks
6. Risk transfer (e.g. through insurance) for specified perils.

This paper focuses on Process Safety Management and Process safety in particular.

There are several process safety guidelines, the most widely used of which, are

* OSHA PSM Rules (USA) Process safety management of highly hazardous chemicals (Federal Register 29 CFR 1910.119)
* EPA Risk Management Programme (USA)
* API RP 750 “Management of Process Hazards”
* CMA System developed by Chemicals Manufacturers Association
* CCPS (Centre for Chemical Process Safety) system under the AIChemE (American Institute of Chemical Engineers).

Modern concepts in process safety MANAGEMENT

Some of the important aspects along with latest current practices are deliberated below:

General and Engineering

  • Layout of Plan - Use of consequence analysis in deciding and finalizing the layout such as segregation between blocks, between tanks, between 2 vessels, between pumps etc. as well as buffer zones. Current practices include exceeding where required minimum legally stipulated values or inter equipment separations. Layouts should also incorporate ease of operations and maintenance as well as minimise piping runs in order to reduce risks. Results of VCE calculations should ensure that process units or trains are located outside the 0.2 bar radius resulting from VCE in adjacent unit or train. Other practices include cooling towers 120 m away from process units or outside the 0.07 bar radius, gas compressors 30 m downwind of fired heaters, deluge valves 15 – 30 m from the plant, pumps atleast 2 m out from under the pipe rack, fire pump atleast 1 m away from the process unit and others.
  • Use of Latest versions of stringent codes and standards during the design as modified with experience. Codes and standards are believed to incorporate large margins of safety inherently. Special design codes include DIERS codes for emergency relief systems in runaway reactors, DPC codes (Deflagration Pressure Controls – Design of vessels for containing a deflagration), DFH Code (Design for Hygiene) where fugitive emissions are critical and many others.
  • Segregation philosophies for different chemicals as inherent safety tool – this includes segregation of offsite and in process storage, but also identify possibilities of incompatible chemicals mixing in drains, vents etc. through techniques such as SPA (Sneak Path Analysis), HAZOP etc. It should also cover management of chemicals in store etc. The effort should show documented evidence that the safest chemicals have been selected (even at the cost of yields) and inventories minimized to the bare minimum. Techniques such as the ICI Hazard Study Model are amongst the best techniques for this purpose.

Process

  • Reaction Hazard Analysis and Reaction Characterization – Latest techniques include
  • DSC, DTA, and other calorimetric tests that could determine presence of exotherms, absence of exotherms under adiabatic conditions, operating to runaway temperature margin, runaway kinetics, impurity profiles, decomposition potentials and thermal stability issues etc.
  • HAZOP study for process – line by line – Latest techniques for HAZOP include the computer HAZOP where the control instrumentation is very elaborate and considers aspects such as tasks, task considerations, task attributes etc. The system studies the control, input/output cards, communication links, operator consoles, power supplies etc. Guidewords in the computer HAZOP include LOW, HIGH, INVARIANT, DRIFTING, etc.
  • Control philosophy, interlocks etc. – latest techniques include HIPS (High Integrity Protective System), 2/3 voting systems, Diversity in measurement / control philosophy, mimic and dummy signals and panels etc. For gas pipelines, techniques for leak detection (LDS), expert systems etc. have become common place. Data on Cathodic systems, anode grounding cells for stray current management, process data etc. are analyzed through expert systems, which can also supervise the entire pipeline shutdown and emergency management system.
  • Backup and redundancy of data – Complex control systems have evolved in the quest for higher efficiency and have largely replaced simple control loops. Data information backup are essential in the use of expert systems which are used to study trends as tools in decision making. Expert systems are now well integrated with conventional control systems. The advent of multi parameter sensing elements and smart instruments has contributed greatly to this effort.

Emergency Containment

  • Identification of emergency scenarios and mitigation measures – Dove tailing of risk analysis and ERP must be ensured so that emergency actions are really specific and focussed and not simple theoretical interludes.
  • Emergency hardware with backup - Important measures include fire protection systems (water, foam, CO2 etc.) and toxic gas containment mechanisms. Conventional systems have rapidly given way to independent PLC Controlled systems and key elements such as detection, warning and activation have improved largely. Passive fire protection techniques such as fire proofing (to limit the temperature of underlying metal to 500 deg. C when it is exposed to hydrocarbon fire for 3 hours), fire proofing of electrical and instrument wiring particularly cables for MOVs (20 minutes for instrument links to ESD) etc. must be available. Other important emergency mechanisms include relief and emergency depressurization, isolation of inventory etc.
  • Response and communication system - Modern systems have replaced traditional telephones and wireless systems, simultaneous data and voice transfer through SCADA, etc. are nowadays prevalent.
  • Fire and emergency medical management
  • Emergency containment system, clothing etc. – requirements for emergency clothing and containment should be dovetailed with Risk Analysis which in turn should dovetail to HAZOP or Hazard Identification for there to be an appropriate action plan.

Operations and Maintenance

  • Preparation of SOPs (Standard Operating Procedures) through JSA (job Safety Analysis) Route – Each task should be studied through JSA and these in turn converted to SOPs with highlights of critical job aspects. These must be available and understood and actually developed by shop floor staff.
  • System for plant modifications and control – These should be well documented and include detailed studies through techniques such as HAZOP for assessing possible changes to the relief / blowdown system, material incompatibility, emergency management issues etc. through a well structured plant modification system.
  • Advanced Preventive and predictive maintenance techniques – Modern techniques for computer based preventive and predictive mechanisms have evolved and have been linked t on or offline vibration measurements, NDT methods (include gamma ray testing, DP, replica tests etc.).
  • Inerting and earthing methods and control mechanisms – These need to be very location and case specific and detailed operating and maintenance manuals should address them.

Management Capability

  • Professionals of standing in key factory positions
  • Empowerment of budget for safety and environment function
  • Working safety organization
  • Near miss recording and reporting system – this is considered perhaps one of the most significant pointers for a strong safety culture.
  • Training and development, stewardship etc. – this sub-element possibly holds the key for strong safety culture
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 Bio-Data
Shri Ganesh Venkatraman, MS (Chemical) has more than 16 years of work experience. He has 50 jobs in QRA and several other jobs in the field of Industrial Safety. He has 12 years old Consultancy firm with experience in World Bank, MoEF and Insurance agencies. He has undertaken projects in India and abroad.