Staffing levels & Workload

Staffing levels

Effective staffing is all about having the right numbers of the right people, in the right place at the right time. It is not just a matter of having enough staff, but also ensuring that they have suitable knowledge, skill and experience to operate safely. The analysis of staffing levels is closely related to several other topics such as workload, organisational change, supervision, competence, interface design and fatigue.

There are two key aspects to this topic:

  1. Determining whether the current levels and distribution of staff are sufficient to ensure health, safety and other goals
  2. Assessing the health and safety implications of proposed changes to existing staffing levels.
Operating room -

As companies reduce staffing levels in order to respond to global economic conditions, there is a danger that individuals become overloaded, and that stress and occupational ill health could result. Insufficient staffing levels will have a detrimental impact on a range of health, safety and performance outcomes. The key principle is that staffing decisions should be made on a sound rational basis, rather than arbitrarily in order to reduce costs, without assessing the implications on health and safety. 

In the UK National Health Service (NHS), the disastrous effects of short staffing on the safety of patients have been witnessed at NHS hospitals such as Mid Staffordshire NHS Trust.  The Health Select Committee Report (2009) states that: “Despite the massive increase in the numbers of NHS staff in recent years, inadequate staffing levels have been major factors in undermining patient safety in a number of notorious cases”. The safety of patients relies on effective nursing care being consistently delivered. This relies on having sufficient nurses with the right skills in place, which depends on robust planning of nursing staff resources.

What are the signs that staffing levels might not be adequate?

  • safety critical tasks are not completed, or they are completed later than they should have been
  • a backlog of maintenance
  • increased overtime levels
  • increased absence due to stress, fatigue and other ill health
  • increased staff turnover due to high workload, stress, and fatigue
  • bottlenecks in communications and
  • increased customer complaints and delivery times.

There is a growing body of research evidence which shows that nurse staffing levels make a difference to patient outcomes (mortality and adverse events), patient experience, quality of care and the efficiency of care delivery. For example, a systematic review in 2007 concluded that there was evidence of an association between increased Registered Nurse (RN) staffing and a lower rate of hospital-related mortality and adverse patient events.

What factors should be considered before reducing staffing levels?

Changes to staffing levels frequently occur as part of organisational change, often referred to as downsizing, delayering or multi-skilling. Before reducing staffing levels, it is important to review and revise risk assessments and action plans to see if the changes could result in new or additional hazards, or increased risk to staff.

Some of the factors that should be considered in risk assessments include:

  • increased job scope for remaining staff, which could exceed their ability to learn and carry out tasks – leading to errors and task omissions
  • failure to retrain remaining staff how to perform new tasks safely and effectively – leading to a lack of staff competence
  • greater reliance on contractors
  • fewer staff with critical skills and knowledge, leading to less resource flexibility
  • more overtime and fewer rest breaks, leading to both physical and mental fatigue
  • overloading staff, especially during periods of high workload, emergent work, and staff absence – leading to errors, task omissions and violations
  • fewer supervisors, leading to a loss of checking for errors
  • fewer staff available to coordinate work and oversee crisis management situations
  • less monitoring – allowing performance problems to go unnoticed
  • less time for some to practice and maintain skills at adequate levels – leading to errors, fewer competent staff, less flexibility to deploy staff, and a greater risk of overloading those staff who can maintain their skills.

Should your organisation have a ‘baseline’?

A concept from the nuclear industry is the staffing ‘baseline’, which is used to demonstrate that facilities have suitable and sufficient organisational structures, staffing and competencies in place to effectively and reliably carry out those activities that could impact on (nuclear) safety. This is sometimes known as the ‘minimum staff complement’. This is a useful concept to consider in any industry if appropriate staffing levels are key to ensuring the safety of staff, contractors, clients or the general public.

To make an assessment about the number of staff needed requires an insight into activities, their criticality, roles, responsibilities and competences. As well as taking into account ‘who does what’, staffing levels will also be affected by how things are done, in terms of the efficiency and effectiveness of processes used.

If staffing levels fall below the baseline (or work demands increase), safety could be affected, and the organisation should have contingency measures in place to address the potential consequences of any shortfall and develop plans to fill the gaps (e.g. recruitment, redeployment, reducing or delaying work, or the use of contract resource). The baseline also provides a reference point against which to assess the potential impact of organisational changes. Further guidance on developing a baseline is provided under More Information.

The dos and don’ts of reducing staffing levels


Assessing staffing levels -
Effective staffing: having the right numbers of the right people, in the right place at the right time.
  • Give staff a role in planning and implementing change
  • Ensure that you have a full understanding of the staffing levels and mix of skills required to operate safely, and use this when agreeing reduction plans
  • Ensure that you understand what tasks need to be performed and what knowledge and skills they require, before planning job mergers and allowing people to take redundancy
  • Have the option to retain key people and skills during the transition period
  • Think about the necessary skills and experiences to ensure the relevant mix of expertise is still available within the company
  • Ensure you have an accurate estimate of peak and emergency workloads when determining how many posts can be eliminated
  • Define a policy for overtime and monitor levels of overtime
  • Set limits on workload and competence for individual roles and monitor their workload
  • Continue to schedule hands-on experience, job rotation, refresher training and competence assessment
  • Proactively monitor the performance of teams and reassess staffing arrangements at a suitable time after implementation (e.g. within six months)
  • Consider the suitability of staffing arrangements in your accident investigations.


  • Ignore the valuable insights from those who actually do the work
  • Set reduction targets solely on the basis of financial considerations
  • Implement an unlimited voluntary redundancy process
  • Reduce staff before ensuring that the skills and expertise continue to be available during the transition period
  • Reduce staffing levels without considering the impact on succession management
  • Base resource estimates solely on ‘normal’ workloads
  • Allow compensatory measures, such as overtime and agency staff, to become the norm
  • Keep piling on tasks until people are overloaded
  • Ignore or forget the need for people to practice their skills and have them assessed, especially where these are important to safety
  • Wait for an accident to happen before accepting that there are performance problems
  • Focus solely on the technical and operability issues in your investigations and assume that staffing levels are a ‘given’.

More information on staffing levels

HSE Guidance – Organisational change and major accident hazards – CHIS7. Information sheet published on the HSE website in July 2003. This is core guidance for major hazard sites and fully applicable to other critical industries.

Assessing the safety of staffing arrangements for process operations in the chemical and allied industries (2001). HSE Contract Research Report 348/2001. This is essential guidance to assist organisations in assessing staffing levels before and after organisational change. It was published when I worked as a Specialist Inspector (Human Factors) for HSE. The Human Factors Team observed that a number of chemical sites were reducing staffing levels in operating teams and expressed concern that such reductions could impact the ability of a site to control abnormal and emergency conditions and may also have a negative effect on human performance through an impact on workload, fatigue, etc.  The need for a practical method for organisations to assess their required staffing levels was addressed by this Research Report. The guidance also enabled HSE Inspectors to apply consistent standards on staffing levels.

Staffing levels and task organisation, Office for Nuclear Regulation, (2014). NS-TAST-GD-061 (Rev2). This Technical Assessment Guide is intended to support ONR inspectors (particularly Human Factors Specialist Inspectors) in assessing a nuclear licencee’s arrangements. It includes assessing the appropriate number of Suitably Qualified and Experienced Persons (SQEPs) and the way tasks are organised to ensure compatibility with human cognitive and physiological characteristics (including the design of shift work systems, workload and team design).

Ensuring the Presence of Sufficient Qualified Staff at Class I Nuclear Facilities – Minimum Staff Complement, Canadian Nuclear Safety Commission (CNSC), July 2007. A Regulatory Guide that sets out the key factors that CNSC staff will take into account when assessing whether a nuclear licensee has made adequate provision for ensuring the presence of a sufficient number of qualified staff. This guide addresses staffing levels required to respond to the most resource-intensive conditions under all operating states, including normal operations, anticipated operational occurrences, design basis accidents, and emergencies.

Developing a staffing baseline. This 2-page guideline outlines the concept of a ‘baseline’ of staffing levels, adopted from the nuclear industry, but applicable to other industries where appropriate staffing levels are key to ensuring health and safety.


Despite much disagreement about its nature and definition, workload remains a key factor in influencing human performance. People tend to define (and thus experience) workload in different ways – perhaps the amount of ‘work’ that is ‘loaded’ on them, the time pressure under which a task is performed, the level of effort exerted, success in meeting task requirements, or the psychological and physiological consequences of the task. So, one person may rate workload based on an assessment of task difficulty, while another’s rating might reflect the level of effort they exerted.

Workload -

Workload can refer to the physical demands created by work or the environment; or it can refer to the mental demands of attending and responding to information. As the pace of technology continues, the physical demands of work are reducing, but the cognitive or mental demands are increasing. For example, the introduction of high levels of technology in many modern vehicles has increased mental workload – both by offering more ‘options’ and by increasing what’s known as secondary tasks (those not related to the primary task of safely controlling the vehicle in a varying environment).

Mental workload has been described as the relationship between the demand for attention resources imposed by a task and the ability to supply those resources by the operator (Moray, 1979). The UK Office for Nuclear Regulation define workload as “The mental and/or physical demands placed on a user by the task requirements, the workplace and the environment (including the organisation)” (ONR, 2014).

Therefore, the workload is used to describe the interaction between an operator and an assigned task. Mental workload is likely to be increased by factors such as time pressure and the need to perform the task correctly.

My experience of workload has mainly been related to my role as a HSE Regulator assessing companies undergoing organisational change; where my main concerns were whether staff would be able to respond to emergencies and upsets; the delegation of more tasks on those staff remaining after downsizing, and whether increased workload would lead to inadequate performance on safety critical tasks.

Workload of control room operators has also been a significant concern, especially in relation to high numbers of alarms following an upset or incident (see Alarm Management). An interesting discussion is whether technology reduces or increases workload. In the control room environment (whether in a process plant, railway signalling centre, air traffic control or elsewhere), people experience variations of workload – often long periods of low activity punctuated by periods of extreme workload. (For more discussion on the impact of technology, see this article The Ironies of Automation).

Although a high workload can cause stress and increase the likelihood of human performance issues, a low workload can reduce engagement and attention – there is a ‘sweet spot’ where demands and capabilities are matched. What we do know for certain is that when demand exceeds supply, human performance declines. There is a need to address this balance in order to reduce any impact on health, safety and other outcomes.

In the CSB investigation report into the BP Texas City disaster, deficiencies in the safety management system that contributed to the unsafe start up included “Insufficient staffing to handle board operator workload during the high-risk time of unit startup”. They also state in this report that:

“Human factors experts have compared operator activities during routine and non-routine conditions and concluded that in an automated plant, workload increases with abnormal conditions such as startups and upsets. For example, one study found that workload more than doubled during upset conditions (Reason, 1997 quoting Connelly, 1997). Startup and upset conditions significantly increased the ISOM Board Operator’s workload on March 23, 2005, which was already nearly full with routine duties, according to BP’s own assessment”.

What needs to be in place to support workload?

Ideally, the following aspects should be in place to enable staff to complete their tasks effectively and balance these requirements with the demands placed upon them:

  • Sufficient attention resources are available to monitor key information and any changes to the expected environment
  • Staff are not bored and able to remain fully alert at all times
  • Staff are physically able to see and reach all equipment that assists in monitoring, controlling and receiving feedback
  • Staff receive information (visual and verbal) clearly, sufficiently, and in good time to assist decision making
  • Conditions should allow incidents /problems to be dealt with effectively. This suggests minimal distractions and work demands that do not impact on both safety and performance
  • People are able to communicate with all staff with whom they have to exchange information
  • People have hours of work and shifts that allow for sufficient rest between and during shifts, to minimise fatigue and maximise attentiveness and effectiveness
  • Equipment is reliable and performs to assist the person’s task.

How do you measure workload?

There are three ways of measuring workload:

  1. performance on a task (e.g. correct and timely performance)
  2. physiological measures, such as heart rate, blood pressure and respiration
  3. subjective reports by those undertaking tasks (e.g. feelings of pressure or significant effort required).

One of the most frequently cited measures of perceived workload was developed by the NASA Human Performance Group and is widely available. NASA Task Load Index (NASA-TLX) is a multi-dimensional scale designed to obtain workload estimates from one or more people while they are performing a task or immediately afterwards. NASA-TLX consists of six subscales that represent somewhat independent clusters of variables: Mental, Physical, and Temporal Demands; Performance, Frustration and Effort. The assumption is that a combination of these dimensions are likely to represent the ‘workload’ experienced by most people performing most tasks.

There are various definitions of the six Rating Scales; I find the following to be understandable to a wide range of users:

  • MENTAL DEMAND (Low/High): How much mental and perceptual activity was required (e.g. thinking, deciding, calculating, remembering, looking, searching, etc.)?  Was the task easy or demanding, simple or complex, exacting or forgiving?
  • PHYSICAL DEMAND (Low/High): How much physical activity was required (e.g. pushing, pulling, turning, controlling, activating, etc.)?  Was the task easy or demanding, slow or brisk, slack or strenuous, restful or laborious?
  • TEMPORAL DEMAND (Low/High): How much time pressure did you feel due to the rate or pace at which the tasks or task elements occurred?  Was the pace slow and leisurely, or rapid and frantic?
  • PERFORMANCE (Good/Poor): How successful do you think you were in performing the task?  How satisfied were you with your performance?
  • FRUSTRATION LEVEL (Low/High): How insecure, discouraged, irritated, stressed and annoyed versus secure, gratified, content, relaxed and complacent did you feel during the task?
  • EFFORT (Low/High): How hard did you have to work (mentally and physically) to accomplish your level of performance?
NASA Task Load Index (NASA-TLX) - App Store -

There are various approaches to applying this method. Although it is possible to ask users to rate each of the above factors separately after performing a task, the NASA-TLX usually involves presenting users with a series of pairs of rating scales (for example Effort and Mental Demands) and asks them to choose which of the items was more important to their experience of workload in the task(s) that they just performed (e.g. “What was the more important contributor to the workload for the task(s) you just performed?”).

The NASA Task Load Index is now available as an App, which makes it easy to identify where in the six sub-scales the workload is originating from. Read more about the App on this page – Measuring workload: There’s an App for that.

Another rating method for assessing workload is the Subjective Workload Assessment Technique (SWAT). This method involves people rating the workload of a task on the basis of the three dimensions of Time Load, Mental Effort Load and Psychological Stress Load.

Time Load: the amount of time pressure experienced in performing a task. This includes the fraction of total available time that a person is busy and the degree to which different aspects of the task overlap or interfere with one another. Under high amounts of Time Load, a user is unable to complete the task due to a shortage of time or interference created by the overlap activities. Time Load is rated on the three point scale below:

  • (1) Often have spare time. Interruptions or overlap among activities occur infrequently or not at all.
  • (2) Occasionally have spare time. Interruptions or overlap among activities occur frequently.
  • (3) Almost never have spare time. Interruptions or overlap among activities are very frequent, or occur all the time.

Mental Effort Load: the amount of attention and/or concentration required to perform a task. Tasks that require Mental Effort Load include storing and recalling things from memory, decision making, calculations, and problem solving. High levels of Mental Effort Load are required in situations that demand total concentration, whereas lower levels of Mental Effort Load are required when the mind wanders or attention is distributed over more than one ‘easy’ task component. Mental Effort Load is rated using the three point scale below:

  • (1) Very little conscious mental effort or concentration required. Activity is almost automatic, requiring little or no attention.
  • (2) Moderate conscious mental effort or concentration required. Complexity of activity is moderately high due to uncertainty, unpredictability, or unfamiliarity. Considerable attention required.
  • (3) Extensive mental effort and concentration are necessary. Very complex activity requiring total attention.

Psychological Stress Load: the presence of confusion, frustration, and/or anxiety which hinders completion of the task. Psychological Stress Load is rated on the three point scale below:

  • (1) Little confusion, risk, frustration, or anxiety exists and can be easily accommodated.
  • (2) Moderate stress due to confusion, frustration, or anxiety noticeably adds to workload. Significant compensation is required to maintain adequate performance.
  • (3) High to very intense stress due to confusion, frustration, or anxiety. High to extreme determination and self-control required.

The above two methods above, NASA-TLX and SWAT are rather subjective and may be time-consuming to apply in practice, but provide an indication of the issues to consider when assessing workload.

Reducing workload – and improving human performance

  1. reduce the demands of the task(s) by reducing the amount of information-processing (such as mental calculations, decisions, or reliance on working memory)
  2. reassigning tasks between team members
  3. remove the need to undertake activities concurrently or in parallel
  4. increase time available for tasks
  5. reduce the complexity of tasks
  6. reduce distractions and unnecessary interruptions
  7. reduce unnecessary alarms and alerts, so that staff do not become ‘flooded’ with demands on their time
  8. simplify the human-machine interface (HMI)
  9. eliminate unnecessary secondary or peripheral tasks (e.g. let voicemail take incoming mobile phone calls when driving)
  10. design procedures according to human factors principles
  11. assess and manage workload early in the design phase
  12. automate aspects of the task, taking care not to introduce different human performance issues (e.g. the use of cruise control can cause different types of accidents).

More information on workload

The NASA Task Load Index (NASA-TLX) is a multi-dimensional rating scale for operators to report their workload. It uses six dimensions of workload to provide diagnostic information about the nature and relative contribution of each dimension in influencing overall operator workload. Operators rate the contribution made by each of six dimensions of workload to identify the intensity of the perceived workload. It is available from the NASA Human Systems Department,

Staffing levels and task organisation, Office for Nuclear Regulation, (ONR, 2014). NS-TAST-GD-061 (Rev2). This Technical Assessment Guide is intended to support ONR inspectors (particularly Human Factors Specialist Inspectors) in assessing a nuclear licencee’s arrangements. It includes assessing the appropriate number of Suitably Qualified and Experienced Persons (SQEPs) and the way tasks are organised to ensure compatibility with human cognitive and physiological characteristics (including the design of shift work systems, workload and team design).

Workload management, Guarding Minds at Work (2020). This checklist aims to support an organisation to create a work environment where assigned tasks and responsibilities can be accomplished successfully within the time available.

Moray, N. E. 1979. Mental Workload: Its Theory and Measurement. New York: Plenum Press.

ISO 10075. 2000. Ergonomic Principles Related to Mental Work-Load. Brussels: CEN.

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