The long awaited update to AIChe’s 2001 foundation text ‘Layer of Protection Analysis – Simplified Process Risk Assessment’ has finally been issued. Entitled ‘Enabling Conditions and Conditional Modifiers in Layer of Protection Analysis’ it clarifies (and, in places, contradicts) the earlier volume.

It takes a different view of ‘time at risk’ factors from the earlier volume, recognising that a fault may occur when a system is not being utilised, but not manifest itself until the system is actually used. This updated approach is in keeping with UK HSE advice following the Buncefield incident.

Useful advice is provided on relating toxic release consequences with fatality potential through the use of the concept of lethal thresholds.

It’s much less helpful on the fraught issue of ignition and explosion probabilities. In our view, the complexity with which this (admittedly genuinely complicated) issue is treated takes it outside the normal understanding of LOPA as a ‘Simplified Process Risk Assessment’.

Nonetheless the volume provides valuable guidance on many issues troubling LOPA practitioners since 2001.