Shiftwork - where employees work at different times and for different durations during a 24-hour cycle - is a necessity for many organizations. So, for example, you might have an electronic system that needs to be fully operational and constantly manned, you might be scheduling nurses for night duty, or public transport may be your area of concern and you have to keep the whole system constantly active. Alternatively, you might have to deliver goods or fresh produce to far-away places in the shortest possible time, or keep a factory running non-stop as it cannot be shut down without serious consequences of one type or another. Whatever the necessity, however, as industrial psychologists our primary interest is the effect shiftwork has on human performance, and our work with clients centers on applying methods that maximize levels of employee alertness during the period worked.

To give you some idea of the importance of getting shiftwork schedules correct, consider the fact that after an employee is awake for 24-hours, with a shift ending at 7.00am, performance declines to a point found with a blood-alcohol level of 0.08%. This is the equivalent to the UK's drink-drive limit. Clearly, this relates to not just work performance but also to issues of quality and error reduction, as well as accident prevention.

The research that we base our work on provides us with many important facts about human functioning in relation to changes in the sleep-wake cycle. For example, we know that alertness declines the longer the time since sleep, and that this is a fixed, linear response. This may seem obvious but because particular employees may appear to be functioning appropriately on an extended duty, organizations may not be fully aware of the consequences of their scheduling or they may apply their policies across the organization with scant regard for how individual differences amongst employees will cause variations in functioning.

While the amount of time on duty is an important consideration, its performance effects become even stronger depending on the particular time of the day the period is worked. The circadian rhythm (the natural cycle of the body's various physiological mechanisms) changes through the day. In general, for many processes such as alertness, the circadian rhythms peak at about 6.00pm and trough at about 6.00am. It is, therefore, not difficult to understand why many more accidents are recorded as occurring in the early hours of the morning, and that these incidents are further exacerbated when employees have worked long hours beforehand.

For Psychonomics designing an effective schedule begins by deciding how the shift needs to run, taking into account how quickly employees should move to a different scheduling rotation and the best type of scheduling rotation. For example, it could be a straight change to working a particular block at night; moving from, say, 9.00am - 5.00pm to then working 9.00pm - 5.00am. But then there is the decision about what to do before - should the employee get one or more days off to set themselves up for the changeover? And then there's the question of whether the employee is actually going to use this time to gear themselves by sleeping? Many don't, not simply because they might treat it as a day or two off work and go shopping, but because they are physically unable to sleep. In cases like these, we would intervene to provide a more intricately designed schedule, as it is often vital - as in safety critical systems - that the employee has had sufficient sleep. This kind of changeover is, in fact, fairly rare. More usually the requirement is for different hours on different days, such as a forward rotation. Here an employee may work 7.00am - 3.00pm on Monday, 3.00pm - 11.00pm on Tuesday, and 11.00pm - 7.00am on Wednesday. Other situations may require a backward rotation or some other combination.

The rotation design Psychonomics formulate is worked out in consultation with senior management according to what the main requirement is. And when it comes to tailoring the overall schedule, we also consider many other factors that include:

	How fatigue effects performance at different times of the 24-hour period
	How the type of task - say, a monitoring task v a manual task - is relevant
	Whether a task is to be done during the night or during the day
	How long an employee is on a particular task within the shift - breaks might be needed
	How long a particular shift should run for
	Whether naps are possible to reinvigorate the body's systems
	Whether the workload is evenly balanced throughout the shift - a higher workload not coming, say, right at the end of a shift
	Whether the organization has made provision for appropriate exercise or rest facilities for during or after the shift (if an operator is looking at a monitor for five hours, is it really restful to have a TV in the relaxation room?)
	The number of rest days required following night shifts when returning to daytime work
	What employees do on their days off shift
	How sickness cover, overtime, and travelling time to and from work, is handled by the organization
	The sleep habits of employees - some people are morning people while others are evening people
	Age and physical fitness, which has an effect on tolerance for shiftwork
	Commitment - employees have to be able to choose whether to do shiftwork, or at the least be able to have an agreed-on compensation
	Nighttime cafeteria provision - if you want people to work appropriately, then they need to be sustained appropriately
	Whether sufficient information has been provided to potential shiftworkers
	The physical characteristics - light levels, noise, odor, temperature - where the shiftwork is to take place

Shiftwork design for Psychonomics is about designing and applying an efficient shift schedule. Together with senior executives we aim to achieve this, while also stressing the need to appreciate the complexity of what is being undertaken and many of the factors that come into play. However, we are also cognizant of the fact that some organizations have very specific shift scheduling requirements, such as the need for airport staff to work extra long or double shifts. Overall, therefore, we work with clients to find the best possible solution that will allow optimal employee performance with the least possible threat to efficiency and safety.