27TH ANNUAL CONFERENCE, Rio De Janeiro, Brazil, 26-29 April 1988
WP No. L003
Night Shift Paralysis in Air Traffic Control
Night Shift paralysis has the effect of temporary incapacitation – even though the subject can both see and hear at the time. Incidence of night shift paralysis had been previously reported to occur in some shift duty workers in other occupations. A questionnaire from Dr. S. Folkhard of Sussex University was distributed to MAs for analysis in Air Traffic Controllers. It was also intended to examine the influence of several factors in order to minimise the occurrence of night shift paralysis.
A total of 435 completed questionnaires from seventeen different countries were subsequently returned. The majority (422) of the respondents were male, reflecting a similar bias in the profession as a whole. Most (294), of them were working in an Area Control Centre (ACC), with a further 103 working in Approach (APP), and 38 in Tower (TWR) facilities. They had a mean age of 35.11 years, and had been working as Air Traffic Control Officers for an average of 13.60 years.
All the respondents had been on their current schedule for a mean of 7.09 years. These work schedules ranged from totally regular, short cycle (e.g. 4 day), shift systems, through longer cycle (up to 189 day) shift systems, to totally irregular work schedules. However, the vast majority of these schedules involved only a single night shift (87.6%). The duration of these night shifts varied from 7 to 13 hours (mean – 10.31 hours). In general, the regular systems rotated in the order ‘Evening-Morning-Night’. Further in many of them a night shift started on the same day as a morning shift.
The reason for this feature is presumably that it maximises the number of successive off- duty days within each cycle of the shift system, but it must clearly contribute to fatigue on the night shift. For the purpose of analyses all the systems reported were classified in terms of (a) their regularity, (b) whether or not a morning and night shift occur on the same day, (c) the duration of the night shift, (d) whether or not a rest break was allowed during the night shift, and (e) the number of successive night shifts that could be worked.
Of the 435 respondents, 26 (6%) claimed to have experienced this paralysis. Most (18) of these individuals claimed to have experienced it only once or twice, but the remainder claimed at least five occurrences, giving a total of 75 occurrences in all. The majority (80%) of occurrences were claimed to have lasted for less than two minutes and only 8 occurrences were judged to have lasted for 5 minutes or more. In the majority of cases the individuals concerned were sure that they were awake at the time (69% of cases), but admitted to feeling sleepier than normal (70%), and were sitting down (86%). During the occurrence their vision was unaffected (76%), they remained aware of their surroundings (88%), they did not experience any strange mental sensations (e.g. hallucinations) (90%), but their limbs ‘felt heavy’ (71%) and some individuals (46%) experienced strange physical sensations such as cold or numbness.
In many cases the individuals became aware of their immobility often in response to some external event (82%). In approximately half the cases, the individuals concerned felt frightened (44%) and were prevented from responding to a work-related event (54%). In about half (55%) of these latter cases it was judged that the inability to respond could have resulted in an accident or near accident. However, in considering this latter figure the relative rarity of this paralysis needs to be taken into account, and there is no evidence of accident or near miss resulting from an ATCO experience of this paralysis.
There was no evidence that the proportion of air traffic control officers claiming to have experienced night shift paralysis was affected be either the facility or country in which they worked. There was a significant correlation between the number of questionnaires returned from a country and the number of individuals from that country claiming to have experienced this immobility, implying that the proportion of individuals experiencing it was relatively constant across the countries. Of the 75 reported occurrences of immobility, 56 took place during the night shift, 12 during the evening shift, and only 7 during the morning shift. Further, there was a trend in the incidence over the course of the night shift, with it building up to reach a maximum at about 0500 hours. This trend was very similar to that previously reported for night nurses.
Effect of Work Schedule
The proportion of individuals claiming to have experienced this immobility appeared to be unaffected by the length of their night shift. Similarly, the provision of rest breaks during the night shift had little effect. However, there was evidence that the number of successive night shifts involved in an individual’s shift system was important. The proportion of individuals claiming to have experienced this paralysis increased from 5.5% of those whose work schedule allowed only a single isolated night shift to 15.6% of those whose schedule involved two or more successive night shifts. There was a marked effect of same day M/N shifts, with the rate increasing from 2.9 % without such shifts through 5.3% when such shifts were allowed in irregular schedules to 11.8% when they were enforced on regular shift systems.
There was an insufficient number (13) of female respondents for the influence of sex to be examined. Nor was there evidence that the incidence was affected by the age of the ATCO, rather than by years of work experience. However, there was evidence that the incidence was affected by ‘personality’ factors.
The questionnaire requested respondents to rate themselves on the degree to which they were ‘flexible’ or ‘rigid’ sleepers, and ‘morning’ or ‘evening’ types. Those claiming to have suffered from immobility had somewhat lower scores on sleep flexibility. Similarly sufferers had marginally higher scores on ‘eveningness’. The immobility was nearly ten times higher in the ‘Rigid Evening Types’ than in the ‘Flexible Morning Types’, the two extreme sub-groups. ‘Rigid’ sleepers experienced this paralysis more than the ‘flexible’ sleepers claiming to have done so. Evening types may have greater difficulty in coping because firstly, they will be inclined to go to bed later than morning types the evening before the morning shift, but are likely to be forced to get up at the same time in order to get to work. Secondly, evening types are less likely to be able to take a nap between the morning shift and the night shift since their level of alertness will be at a maximum at this time, thus sleep depriving evening types to a greater extent than morning types, thus suggesting that evening types should be limited to work schedules that include single day M/N shifts.
Although the overall incidence (5.98%) of night shift paralysis found in the present study was approximately half that previously reported for night nurses, this comparison tails to take account of the number of consecutive night shifts involved which was far greater for the nurses. If allowance is made for this factor, then the incidence in the present study was approximately three times as high as that in the nurses’ study. Thus it would appear that night working males are indeed more prone to this paralysis than their female counterparts. The incidence in the present study was found to depend on four factors that might be expected to influence an individual’s level of sleepiness or sleep deprivation. These were the time of night, the number of consecutive night shifts, the occurrence of both a morning and a night shift on the same day, and individual differences in sleep and, to a lesser extent, ‘morningness’.
Subjectively – rated alertness shows a marked circadian (daily) rhythm, which is at least partially independent of the normal sleep/wake cycle, and that alertness is low in the early hours of the morning. Similarly, there is good evidence that the duration of day sleeps taken between two successive night shifts are considerably shorter than normal night sleeps. Thus there will be a cumulative partial sleep deprivation over successive night shifts. Further, there is also evidence that night sleeps preceding a morning shift are shorter than normal ones. Finally, rigid sleepers, and especially those who are also evening types, are less likely to be able to sleep successfully prior to a night shift.
It thus seems reasonable to conclude that the incidence of this paralysis may indeed be a useful reflection of the level of sleep deprivation associated with different shift systems. Further, the present results suggest that this potentially dangerous sleep deprivation could be reduced by limiting the number of successive night shifts to one and by ensuring that no individual is allowed to work both a morning and a night shift on the same day.
A temporary but incapacitating paralysis known as ‘night shift paralysis’ appears to be a special form of sleep paralysis that occurs when night workers manage to maintain a state of wakefulness despite considerable pressures to sleep. The incidence of this paralysis might thus be assumed to reflect the level of sleep deprivation associated with different shift systems or individuals. The present survey was designed to examine this possibility in a sample of 435 Air Traffic Control Officers (ATCOs) from seventeen different countries who were on a variety of different work schedules. The incidence of this paralysis was found to be affected by four main factors, all of which might reasonably be assumed to influence the night-worker’s level of sleep deprivation or sleepiness.
a) Time of night (most common at around 0500 hours);
b) Number of consecutive night shifts in the work schedule. (Single nights produced the least effect);
c) Same day M/N shifts (a markedly noticeable increase);
d) Individual personality difference (greatest effect on rigid sleeper ‘evening’ types, least on flexible sleeper ‘morning’ types).
Shift systems should not include night shifts that commence on the same day that a morning shift ends.
Shift systems should include preferably single night duties only, but where consecutive nights are required, they should be restricted to the minimum.
In respect of the nature of night shift duties, MA’s should pursue additional time off for night shift worked as compensation.
Last Update: September 20, 2020