Process safety

Process driven

An essential element of managing high-hazard installations is process safety, but can it be applied usefully to smaller systems?


Process safety management mixes engineering and systems skills to prevent catastrophic accidents, such as explosions, fires and toxic releases from installations including chemical plants and oil and gas facilities. Its importance is best illustrated by the frequency process safety failures are cited in inquiry reports into major incidents such as the explosions in 2005 at the Buncefield oil terminal in the UK and BP’s Texas City refinery in the US.

The UK-based Energy Institute has defined four pillars of process safety: leadership; risk identification and assessment; risk management; and review and improvement. Safety and health practitioners will note that the pillars correlate to the more common systems models: plan, do, check, act, or POPIMAR (policy, organisation, planning, implementation, monitor and review).

Process safety metrics and techniques have a utility that stretches beyond the specialised applications they are usually associated with. The burden of effort and reward might not always be the best use of a practitioner’s time so they are not applicable to every system or hazard. But if you are dealing with systems such as local exhaust ventilation, manufacturing plant or any process that could create an explosive atmosphere, they may be useful tools to help you to identify and visualise the shortfalls and correct them.

Tower tour

Take the example of the maintenance, dosing, and sampling of evaporative cooling towers to prevent the growth of Legionella. The first stage of the process safety approach is to understand the hazards and consequences we want to avoid. The Health and Safety Executive’s (HSE) approved code of practice L8 (bit.ly/2y57gD1) describes the risks of the multiplication of naturally occurring Legionella pneumophila bacteria in evaporative cooling systems leading to the risk of people contracting legionnaires’ disease from breathing in aerosoled droplets of water expelled from cooling towers.

Having identified the hazard, the next stage is to describe the control measures – preferably engineering solutions – that have been or will be implemented to prevent the hazard occurring. In process safety terms they would refer to this equipment as “safety critical”. At this stage, process safety will go further into the engineering measures than traditional safety practitioners may consider necessary, looking at failure modes of the engineering and the required maintenance and inspection regime needed to maintain the control.

For cooling towers, these critical elements of engineering control are defined in the HSE’s technical guides HSG274 (bit.ly/2fQFwbv). In process safety terms, the items of a cooling tower structure – drift eliminators, distribution system, tower packing, pumps, automatic dosing system, and recirculated water system pipework – all become critical engineering features that must be maintained.

It is not just the condition and cleanliness of these critical features that need to be monitored, it is also the maintenance activities that ensure the facilities remain available and in the right condition. The same can be applied to the operational controls, such as sampling or pump rotation.

Upwards reporting needs to make the gaps in control visible, with increasing urgency the more gaps there are

Leading by example

When you have identified a control measure structure, you can reflect it in a set of leading and lagging indicators to monitor its effectiveness.

Leading indicators for an evaporative cooling system include:

  • completion of maintenance tasks such as cleaning, pump maintenance and dosing equipment calibration
  • operational tasks such as sampling, biocide changeover and pump rotation
  • information from borescope camera inspections of the tower packing
  • cooling water chemistry trends – levels of dissolved and suspended solids that can feed bacteria, acidity/alkalinity and calcium concentration
  • number and competency of responsible persons supporting the operation of the cooling tower system
  • the quality of the risk assessment and written scheme.

Lagging indicators are:

  • Legionella and bacterial level sampling results
  • level of biocide reserve in the system.

These parameters, referred to as process safety performance indicators (PSPIs), provide a view of the breadth of organisational arrangements that ensure control of Legionella in the system rather than just waiting for system sampling results, as is the case in many organisations.

The PSPIs can be reflected in a dashboard or operational chart that enables changes, omissions and deviations to be highlighted and addressed. If these deviations are tackled as they arise, say after identifying an instance of missed maintenance or cleaning, there is less chance of an incident occurring.

Widely applicable

The same approach could be applied to many other situations that rely on engineering to control exposure to hazardous substances in an office building or maintain its temperature. In the case of a large ventilation system, PSPIs could include:

Leading indicators

  • completion of scheduled maintenance (fan servicing, filter replacement)
  • inspections to ensure material does not build up in ducts
  • measurements after maintenance to ensure fan velocities and air temperatures are maintained within desired parameters
  • completion of workplace environmental monitoring such as temperatures and bacterial levels.

Lagging indicators

  • workplace or personal exposure monitoring results
  • complaints about workplace environment relevant to ventilation system.

Once the controls are mapped, along with the activities to ensure they are maintained, the next challenge is to ensure it is a priority for leaders, so that they influence the organisation and make sure any shortfalls are corrected. This mechanism is lacking in many organisations.

Process safety tools cannot ensure leadership commitment, but by tabulating the controls and the performance of them the reduction in barriers can be documented.

In our cooling towers example, the HSE defines the performance requirements and standards can be assessed against parameters defined as “good”, “probably acceptable”, “caution”, or “high risk”, with which makes mapping easy. In other systems a measure such as overdue maintenance is more difficult to classify. It would seem sensible to set a rising level of severity the longer the operation is due.

Upward reporting needs to make the gaps in control visible, with increasing urgency the more gaps there are. For the cooling tower, reporting is grouped into three areas: treatment programme, asset condition and inspection, and Legionella management. These should be broken down further into the elements that contribute to these three primary areas of control. This report provides a reference to operational performance on a given area or hazard and serves as an operational control tool that is more detailed and better focused than accident records or audit metrics.


Joshua Rice is chair of IOSH’s Hazardous Industries Group


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