How to Mitigate the Risks Due to the Implementation of New Technologies

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Risk Assessment in ULSD

Considering, a refiner is deciding to implement Ultra Low Sulphur Diesel (ULSD) technology in his refinery, a simple technical risk assessment has been done in Table 3. The refiner or plant operator in the general case has to systematically ask himself what the risks are and whether he can accept these risks. The main risks are whether the refiner will be able to produce ULSD that meets ATSM specifications using the technologies available in the market.

Risk Management in Plant Safety

In the design of operating units, the well known ‘Hazard and Operability’ (HAZOP) and ‘What-If’ studies are performed to assess the safety of unit designs or changes to units. These studies examine 100 per cent of the potential event outcomes, but are however purely qualitative. For example, a HAZOP study may indicate that a relief valve must be installed to prevent tank overpressure and tank rupture.

Simplified-quantitative methods use relative rankings of hazards to evaluate the hazard potential of installations or changes to installations. These include the Chemical Exposure Index (CEI) and the Fire & Explosion Index (F&EI). The CEI would provide a relative hazard ranking – in case the tank ruptured and released its content into the atmosphere compared to releases of other chemicals. Moreover, Layer of Protection Analysis (LOPA) would identify independent layers of protection that would reduce the risk over tank overpressure.

An Independent Protection Layer (IPL) is defined as ‘a device, system, or action that is capable of preventing a scenario from proceeding to its undesired consequence independent of the initiating event or the action of any other layer of protection associated with the scenario.’

Examples of IPLs include relief valves (RVs), which prevent the system exceeding specified overpressure. The PFD for an RV is for example 1 out of 100. Thus by fixing an RV, the risk of overpressure is reduced by a factor of 10-2. LOPA is also semi-quantitative and assigns orders of magnitude to Probabilities of Failure on Demand (PFD) of independent layers of protection. LOPA can be used in any stage in process development, but is most frequently used in the design stage when PIDs are complete. This is used to examine scenarios generated by qualitative process hazard tools – when the consequences are not clear, the frequency of the final consequences is unknown or when processes are too complex to address qualitatively. LOPA, CEI and F&EI are applied to 10-20 per cent of the scenarios taken in HAZOP analysis. Full quantitative risk analysis (CPQRA) is applied to a small percentage of the potential situations. This analysis is used to help evaluate potential risks when qualitative methods cannot provide adequate understanding of the risks and more information is needed. Quantitative risk analysis includes statistical and probabilistic modelling of frequency and consequence of a single scenario. Thus, in case of tank rupture and release of its content, CPQRA would determine the number of fatalities at a distance (of say 1000 m) away from the unit, and the frequency of this occurrence.

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