a paper presented to the international railway safety conference tokyo 2002 by dennis bevin rail...

A paper presented to the International Railway Safety A paper presented to the International Railway Safety Conference Tokyo 2002Conference Tokyo 2002

by Dennis Bevinby Dennis BevinRail Accident InvestigatorRail Accident Investigator

MICROSLEEPMICROSLEEPA small sleep... a BIG problem

1.1. INTRODUCTIONINTRODUCTION

WestmereWestmereTwo locomotives at the head end of a train rolled and five trailing wagons were derailed.

The incidents being used as case studies resulted in the following:

Kai IwiKai IwiTen loaded milk tankers rolled and slid down an embankment.

MiddletonMiddletonTwo locomotives and several wagons were damaged and derailed as a result of a head on collision.

2.2. BACKGROUND BACKGROUND

“A brief unintentional period of light sleep, lasting from seconds to minutes, during which the eyes may be open but the brain is disengaged and is not processing information. The causes of microsleeps are directly related to fatigue”.

What is Microsleep? What is Microsleep?

2.2. BACKGROUND BACKGROUND

• Extended wakefulness.

Method for assessing fatigue Method for assessing fatigue

Fatigue assessment was based on a method developed by the US National Transportation Safety Board and the NASA Countermeasures Program.

• Acute sleep loss and cumulative sleep debt.

• Presence of a sleep disorder.

• Critical times in the daily cycle of the circadian body clock.

This method seeks information on the following factors known to produce fatigue-related performance impairment:

An express freight train derailed near Kai Iwi while rounding a curve about 25 km/h faster than the authorised and posted curve speed of 50 km/h.

3.3. CASE STUDIESCASE STUDIESWestmere and Kai IwiWestmere and Kai Iwi

An express freight train derailed when travelling too fast for the first curve encountered descending a 1 in 35 grade near Westmere.

The reason for the excessive speed in both cases was the LE’s loss of awareness during a microsleep.

3.3. CASE STUDIESCASE STUDIES

• The control of LEs hours.

Westmere and Kai IwiWestmere and Kai Iwi

Safety issues identified included:

• Fatigue management.

• The ability of the locomotive’s vigilance system to overcome a short-term attention deficit in sufficient time to allow effective corrective action to be taken.

The passing of the signal resulted from the LE’s loss of attention and situational awareness consistent with his having fallen asleep.


• The control of LEs hours.

MiddletonMiddleton

A northbound express freight train passed Signal 212 at Middleton at “Danger” and collided head-on with a departing southbound express freight train.

Safety issues identified again included:

• Fatigue management.

• The ability of the locomotive’s vigilance system to overcome a short-term attention deficit in sufficient time to prevent this type of collision.

from Addington

to Addington

Middleton yard

down main line to Rolleston

up main line from RollestonSignal 202

Signal 212

MiddletonMiddleton Setting the sceneSetting the scene

3.3. CASECASE STUDIESSTUDIES

route set for Train 951

Signal 212

Overbridge

down main

up main line

112 seconds from impact, travelling at 56 km/h, the LE cancelled the visual vigilance device by moving the throttle

from notch 6 to notch 5.

90 seconds from impact, travelling at 57 km/h Train 828 passed Signal 1712 at

yellow.

56 seconds from impact and travelling at 59 km/h the LE cancelled visual vigilance by operating throttle (automatic

reflex?).

54 seconds from impact and while travelling at 59 km/h

the LE entered a microsleep

43 seconds from impact and travelling at 59 km/h the LE had a memory of Train 828

emerging from under overbridge.

POINT OF IMPACT

20 seconds from impact – while travelling at 58 km/h the LE

has become fully aware of the situation and applied the

emergency brakes.

MiddletonMiddleton Time sequence of eventsTime sequence of events

Relief shifts and standbys were built in to allow for annual leave, sickness and operational demands.

3.3. CASE STUDIESCASE STUDIESMiddleton Middleton

LEs base rosters were compiled using defined principles of fatigue management, with fortnightly rostered shifts at or about 80 hours.

Mini rosters were compiled for each LE and included changes to the base roster to accommodate staff availability and operational requirements. Actual hours worked could vary from those rostered due to late running and other operational factors on the day.

The Locomotive Engineer’s rosterThe Locomotive Engineer’s roster


Mini - rostered shifts Mini - rostered hours Actual hours worked

Day 1 Off by request Nil Nil

Day 2 1300 - 1700 4 hours 4 hours

Day 3 0820 - 1900 10 hours 40 mins 11 hours 20 mins










Total 86 hours 40 mins 91 hours 30 mins

Day 13 2040 - 0500 8 hours 20 mins

Day 14 2345 - 0855 9 hours 10 mins

MiddletonMiddleton

The mini-rostered hours and those actually worked by the LE prior to the incident are shown in the following table:

The Locomotive Engineer’s rosterThe Locomotive Engineer’s roster

German study suggests that an LE’s vigilance is at its worst in the early hours of the morning.

4.4. Factors that increase the Factors that increase the likelihood of falling asleep likelihood of falling asleep

uncontrollablyuncontrollably

Time of dayTime of day

Biological sleepiness waxes and wanes across the daily cycle of the circadian body clock. People are most prone to falling asleep inadvertently in the early hours of the morning and again in mid - afternoon.

The German study also found that how long an LE had been on shift affected how impaired his alertness became in the early hours

of the morning.



Time on shiftTime on shift

The accuracy of information on an LE’s sleep history can be limited by the following factors:

• Subjective reports of sleep duration and timing are not necessarily reliable.

Laboratory studies consistently show that biological sleepiness increases the longer a person stays awake (sleep history).

Duration of continuous wakefulnessDuration of continuous wakefulness

• The length of time from the first of the sleep episodes being recalled to the time of the interview.

• The length of time between the incident and the interview by the investigator.



Getting 2 hours less sleep than they need on one night is enough to impair most people’s performance and alertness the next day.

Insufficient prior sleep increases biological sleepiness at all times in the circadian body clock cycle.


uncontrollablyuncontrollablyPrior sleep lossPrior sleep loss

It typically takes 2 full nights for sleep and daytime functioning to return to normal after sleep loss.

Sleep that is restless and fragmented by frequent awakenings also leaves a person sleepy and at increased risk of impaired alertness and performance.



Presence of a sleep disorder/quality of sleepPresence of a sleep disorder/quality of sleep

The restorative value of sleep, in terms of reducing biological sleepiness and improving subsequent waking function, depends not only on the amount of sleep obtained but also on its quality.

5.5. ROSTERING ISSUESROSTERING ISSUES

The amount of sleep that a person can obtain during a break is highly dependent on the time of day at which the break occurs.

Forward rotation and short breaks Forward rotation and short breaks between shiftsbetween shifts

Forward rotations of shifts reduced the likelihood of very short breaks between shifts, which can restrict the time available for sleep.

Westmere Westmere The LE’s previous 4 shifts had resulted in each train running an average of 1 hour 36 minutes late.

5.5. ROSTERING ISSUESROSTERING ISSUESLate runningLate running

Late running, particularly after night shifts, reduces the time available for sleep and can contribute to the accumulation of sleep debt across consecutive shifts.

Kai Iwi Kai Iwi The LE’s previous 4 shifts had resulted in trains running an average of 55 minutes late.

Middleton Middleton Of the LE’s previous 5 shifts 4 had resulted in trains running an average of 38 minutes late.

There can be numerous reasons why LEs agree to work extra shifts over and above those for which they are originally rostered.


Working on rostered days offWorking on rostered days off

• concern about possible effects of refusal on relationships with other locomotive engineers, or with the company


• remuneration incentives

These include:

• loyalty to fellow locomotive engineers at the depot, who may be less well-rested or have important commitments away from work

• professional motivation to ensure that the system runs smoothly

• loyalty to the company.

Westmere Westmere The LE was called back on a rostered day off duty between two night shift cycles to work a day shift.

5.5. ROSTERING ISSUESROSTERING ISSUESWorking on rostered days offWorking on rostered days off

Additional shifts prior to a block of night shifts prevent an LE from being well rested going into the night shifts.

Middleton Middleton The LE had worked both of his rostered days off the preceding weekend and both of these extra shifts had involved night work.

Westmere Westmere The LE had been called back on a rostered day off between two night shift cycles to work a day shift which, although it did not directly restrict his nighttime sleep, would have restricted his opportunities for rest and recovery between the night shift cycles.

5.5. ROSTERING ISSUESROSTERING ISSUESOpportunities for recovery from sleep debtOpportunities for recovery from sleep debt

For daytime functioning to return to normal after sleep loss it typically takes 2 full nights of sleep.

Middleton Middleton In the month preceding the collision the LE had been rostered off duty for one 4-day block during that time but had worked day 2 and day 4 of that block. He had also been rostered off duty for one further 2-day block but had worked both of these days. In that time he had only 1 break of at least 48 hours free from work.

6.6. FINDINGSFINDINGS

• The accident occurred at a time when the LE’s biological sleepiness would be expected to be increasing rapidly towards its daily maximum (3)

The following factors were identified from the 3 investigations. The number in brackets indicate the number of investigations to which each finding was relevant:

• The LE lost attention and situational awareness as a result of falling asleep through fatigue (3)

• The LE was probably experiencing the effect of an accumulated sleep debt at the commencement of his shift (3)

• The LE’s increase in sleepiness due to the daily cycle of his body clock would have been exacerbated by his prior sleep loss, and by his being between three and a half hours and six hours into his shift (3)


• The base rostered hours for the LE were excessive (2)

• The mini rostered hours for the LE were excessive (2)

• The actual fortnightly hours which would have been worked by the LE had the accident not happened would have been excessive (2)

• The LE responded to a request to work on his rostered days off duty in the days prior to his accident (2)


• The current locomotive vigilance system did not provide an effective defence against short microsleeps (3)

• The operator had no process in place to monitor and control total mini-rostered hours and actual hours worked each fortnight (3)

7.7. SUMMARYSUMMARYThis table compares aspects of the 3 case studies:

Westmere Derailment Kai Iwi Derailment Middleton Collision

Time of day

2330 0105 0400

Time on shift

4 hours 3 hr 25 mins 6 hr

Completed shifts since last

2- night break

4 4 10

Late running on prior night shifts

4/4 (average 1 hr 36 mins)

4/4 (average 55 min)

4/5 (average 38 min)

Rostered days off worked

1/2 (12 days)*

0/0 (4 days after

returning from leave)*

3/4 (11 days)*

Consecutive night shifts including shift on which the accident happened

5 5 5

* Denotes days prior to accident

MiddletonMiddletonThe LE fell asleep after passing a “caution proceed” signal, waking as he approached the next signal at “Danger”, but too late to stop his train before it collided with an oncoming train.

7.7. SUMMARYSUMMARY

Westmere and Kai Iwi Westmere and Kai Iwi The LEs fell asleep near the top of an ascending grade, and then did not brake.

• they occurred between 3 hours 30 minutes and 6 hours into a night shift that was between the 5th and 10th in a sequence of night shifts

7.7. SUMMARYSUMMARY

These incidents all had in common:

• the LE’s preceding night shift had also run late

• they all occurred at or near the daily peak in biological sleepiness

• the reduction of staff numbers or a general staff shortage which may require remaining staff to perhaps work longer and more often

7.7. SUMMARYSUMMARY

There are commercial factors which have the potential to increase the risk of microsleeps amongst LEs:

• the introduction of single person crewing

• the requirement for increased overnight services to match competitors’ service

8.8. CONCLUSIONCONCLUSION

• they were unaware they had happened

There has been traditionally a low level of reporting microsleeps on the part of LEs, due to:

• fear of the Company’s response

• underating the significance

Although the Commission has not investigated any previous accidents or incidents where microsleep was an obvious causal factor, there has long been anecdotal evidence from other investigations carried out that microsleeps were occurring frequently.



• It is developing an improved fatigue management program which it plans to put all Locomotive Engineers through

For it’s part the operator in New Zealand is taking positive steps towards both educating staff and developing procedures to counter the causes of microsleeps:

• It has introduced new processes within the roster centre to monitor mini rostered and actual work hours on an ongoing basis

• A joint working party between the Union and the Company has designed new rostering procedures which limit the number of consecutive night shifts that can be worked and defined the minimum rest period which must then be enforced.

To prevent . . .

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www.taic.org.nz

a paper presented to the international railway safety conference tokyo 2002 by dennis bevin rail...

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