SPADs and Safety Critical Communications

Clear spoken safety critical communications can help reduce SPAD risk. Communication issues were found to have caused, or contributed, to 17% of SPAD incidents. This article looks at some of these issues and examines how the idea of a ‘contract’ can help strengthen safety critical communications.

The following are some examples of how mis-communications can contribute to a SPAD (adapted from RSSB T1128 and RSSB’s “Review of causes behind an increase in signals passed at danger occurring in Period 3 2018”):

  • When speaking to the signaller, the driver misunderstood the type of bridge to check for following a reported bridge strike. The signaller used the term ‘span’ which led the driver to believe he was looking for an overbridge which was further away. As the driver proceeded towards what he thought was the correct bridge, he passed the signal at danger because he was focussed on identifying the correct ‘span’.
  • A driver took information from an unauthorised person to pass the signal at danger, assuming the details had come from the signaller, but this was not the case. The driver should have noted that it was unusual to receive a message from a member of platform staff, and that they were passing a signal without the correct authority. 
  • Following a conversation with a shunter, a driver thought that the signal he could move forward to was one he could only see the back of.  When the driver did move the unit forward, he passed a signal that he had not seen, which was at danger.  This triggered an alarm in the signal-box, leading the signaller to call the driver to stop the move.
  • A signaller informed a driver that he would be given permission to pass the signal at danger. The signaller used the words ‘authorised’ and ‘my permission’ in explaining the movements, but this was before the signaller formally gave permission. This contributed to the driver believing that he had permission and proceeding forward in advance of the formal permission being given.

Fortunately, much work has been done by the industry to enable good verbal safety critical communications. To support this work, there is a dedicated RSSB web page on safety critical communications, where you can find details a learning support pack and a manual on the topic. 

The manual moves the focus of good communication performance beyond the use of techniques such as using the phonetic alphabet and speaking numbers singly. It introduces the idea that safety critical communications are about forming a contract between two parties and agreeing a course of action. The process of stating messages clearly, checking understanding, repeating back, and coming to a clear understanding is all about agreeing a verbal contract. In practice this means conversations should:  

  • identify the parties involved
  • provide information about the situation
  • agree the actions to be taken
  • confirm the agreement 
  • check that a full understanding has been reached by both parties 

The manual provides guidance on how to support safety critical personnel develop the right skills. It includes cue cards, scripts, and good practice examples for high risk activities.

Haven’t found what you’re looking for?
Get in touch with our Principal Human Factors Specialist for further information.
Philippa Murphy
Tel: 020 3142 5641
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