All trains that had a guard will have a OBS rostered to it, roster error isn't an exceptional circumstance, also strike days are not an exceptional circumstance.
Exceptional circumstances
reduced to three exceptions,
:: Late notification of sickness, defined as less than two hours before booking on time;
:: On board supervisor (OBS) displaced by service disruption, late-running trains or being left behind on a platform;
:: OBS unable to continue duty having started work, for example through sickness, or having to leave the service to help a passenger or deal with an emergency.
Exceptional circumstances
reduced to three exceptions,
:: Late notification of sickness, defined as less than two hours before booking on time;
:: On board supervisor (OBS) displaced by service disruption, late-running trains or being left behind on a platform;
:: OBS unable to continue duty having started work, for example through sickness, or having to leave the service to help a passenger or deal with an emergency.