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The problem with alarms Alarm management was a key topic in my previous role inspecting high-hazard facilities, and the UK HSE team provided input into a detailed publication by EEMUA (Engineering Equipment & Materials Users Association), published in 1999. This document, known as EEMUA Publication 191, became the authoritative reference, and I used this document in my inspections of alarm systems. HSE provided a summary information sheet in 2000 (“Better Alarm Handling”, CHIS6). When interfaces are designed, there may be an assumption that control room operators will always detect an alarm, know what action to take, and respond in a timely manner. However, we know from several incidents around the world that this is not always the case. For those industries that have a safety case or a safety report, it’s important not to make significant claims for operator response to alarms, unless you can demonstrate a high level of human reliability. Despite the fact that clear, detailed guidance has been available for over 25 years, this still remains a key factor in major events. I’ve just been reviewing the latest CSB investigation report into the naphtha release and fire at the Husky Toledo refinery in Ohio. On 20 September 2022, flammable liquid naphtha was released from a pressure vessel, and the vapour cloud ignited causing a flash fire. This incident fatally injured two employees, who were brothers. The incident also caused $597 million in property damage. One of the key findings of the CSB report relates to the management of alarms. It is commonly accepted that more than 10 alarms in 10 minutes is considered an “alarm flood”, when more alarms are presented than can be addressed by a single person. This target was documented in the company’s own guidance on alarms. The impact of an alarm flood is that operators are more likely to miss critical alarms or misdiagnose the situation. At the Husky Toledo incident, control room operators were almost certainly overwhelmed by alarms. On the day of the incident, between 0650am and 1849pm, a total of 3,712 alarms were recorded. In other words, the operators experienced alarm flood for a continuous 12 hours. At a critical time during the event, the six most frequent alarms accounted for nearly half of the alarm annunciations. “The high extent and duration of alarm flood contributed to the incident by overloading the board operators, contributing to miscommunication, errors, and missed alarms, ultimately leading to the fatal incident” (CSB, June 2024, p.102). If you have an alarm system, the EEMUA and HSE guidance provide an approach to help understand if you have a problem - and how to address it. Martin Anderson is a Principal Consultant, working at the intersection of human factors and process safety. #humanfactors #safety #safetyleadership #processsafety  https://lnkd.in/gCDnHHmq

EEMUA Publication 191 Digital

EEMUA Publication 191 Digital

eemua.org

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