ATSB – RO-2018-004
the driver said he had a voluntary annual medical check with his local general practitioner. At the initial ATSB interview in February 2018, the driver stated that he was a person in good health, using no medication, with no previous history of blackouts or sleep disorders.
The health assessment standard covers a wide range of medical conditions that may impact on safe working performance. It seeks to provide guidance to support consistent assessment and decision-making. It is reviewed approximately every 5 years to ensure the medical criteria are up to date with the latest knowledge and research. The areas of interest to this investigation are contained in part 18 of the standard – 'Conditions causing sudden incapacity or loss or situational awareness'. The following are the sub-headings for this part:
- Blackouts
- Cardiovascular conditions
- Diabetes
- Neurological conditions
- Psychiatric conditions
- Sleep disorders
- Substance misuse and dependence. [1]
The investigation considered the following were the most likely reason for the driver's lack of input to the braking controls as he approached the buffer stop:
- the driver experienced a blackout
- the driver had a microsleep due to fatigue impairment
- the driver was inattentive or distracted.
Due to the lack of any CCTV inside the cab, the investigation could not conclusively determine what happened to the driver. The following is an analysis of the likely reason for the lack of braking input by the driver as the train approached the buffer stop.
A blackout is described as an unpredictable, spontaneous loss of consciousness. The National Standard for Health Assessment of Rail Safety Workers states that 'blackouts or pre-syncope may indicate an underlying medical condition (e.g. seizures, diabetes, cardiovascular condition, a sleep disorder)'. [2] It is possible that the blackout was related to the obstructive sleep apnea that the driver was diagnosed with after the incident. As described previously, the medical testing conducted on the driver after the event found no abnormalities with the driver's cardiological or neurological condition.
One type of blackout is termed 'syncope'. This temporary loss of consciousness is usually related to insufficient blood flow to the brain. It is commonly referred to as fainting or passing out. It often occurs when blood pressure is too low and the heart does not pump enough oxygen to the brain. 'Fainting is a common problem, accounting for 3% of emergency room visits and 6% of hospital admissions. It can happen in otherwise healthy people. A person may feel faint and lightheaded (pre-syncope) or lose consciousness (syncope).' [3]
The driver's original description of the event leading up to the collision was similar to that which can occur with low blood pressure. In the crucial time approaching the station the driver stated that he 'felt dark, dizzy and powerless, and that my body had no control over me. I felt complete black, dark. I don't know what happened to me after that.' He also said that when he regained his senses he saw the buffer stop about one car-length away, and applied the brakes to maximum.
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- ↑ National Transport Commission (2017). National Standard for Health Assessment of Rail Safety Workers. p.72.
- ↑ National Transport Commission (2017). National Standard for Health Assessment of Rail Safety Workers. p.72.
- ↑ https://www.webmd.com/brain/understanding-fainting-basics#1
