HFE Specifications

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In my article on human factors input into a 3D model review of a proposed design, I noted the importance of agreeing on a specification of human factors requirements. Here, I’m going to unpack what these specifications might look like in more detail, and provide some example specifications.

Typically, for the design of a large facility that relies heavily on operator intervention (such as an offshore platform, a nuclear power plant or railway control centre), a specification for Human Factors Engineering (HFE) will be drawn up for the project. This document may be based on several international and national standards, together with industry standards. It may simply duplicate criteria from these existing documents, but formalising what criteria are to be used for the project is a key milestone.

HFE specifications may also be drawn up for product design, such as in the development of medical equipment, a power tool, a forklift truck, or other vehicle.

These specifications will outline general requirements (or principles) together with extremely specific dimensions and design details. The specifications for a project will of course depend upon the nature of the facility or product to be designed.

They should be agreed early in the project, as a key role of the human factors specialist is to ensure that these are met throughout the design. The HFE specifications that will apply for a particular project will be documented in the Human Factors Integration Plan (HFIP).

These specifications and related assessment studies are sometimes referred to as “Working Environment” rather than Human Factors Engineering. For example, the Norwegian standard NORSOK S-002 is often referred to in the design of offshore petroleum facilities in Norwegian waters and elsewhere. This NORSOK S-002 standard uses the term Working Environment, which it defines as:

“the totality of all physical, chemical, biological and psychological factors at work that may affect employee health and well-being through acute or lasting exposure“.

The contents of a HFE Specification

In my article on Human Factors Engineering, I noted that two areas need to be considered when developing or reviewing a design. First, we have the physical aspects – these relate to how the design supports people to do things. Second, there are cognitive aspects – how well the design supports people to make the right decisions. Let’s consider how a design specification for these two aspects can support effective human performance (for both doing and thinking).

The physical aspects of a design (often anthropometrics or biomechanical characteristics) that are included in a specification typically address five main areas:

1. Clearance: the space available to undertake tasks (which includes clearance for the people involved, their PPE and any tools or equipment)
2. Reach: the distance that a user has to reach to access equipment or controls
3. Posture: the postures that the user will have to adopt in order to interact with equipment
4. Strength: the forces required to interact with the equipment, such as turning a valve handle
5. Access: the area where work is undertaken needs to be accessible, free of potential hazards and the pathway to it has to be clear.

For example, the specification may provide guidance on how wide walkways need to be, how high a control can be mounted, the ideal location for displays, the amount of force needed to close a valve, the angle of inclination for stairs, the height of handrails, the direction in which doors open, or the maximum temperature of a hot surface.

The specification may depend upon the nature of the user and the context. For example, when designing seating on public transport, the seats for passengers can be fixed, but it would be preferable to provide adjustable seating for the driver.

Computer Aided Design (CAD) tools are helpful to assess the suitability of a design, by creating a mock-up of the work area, equipment and potential users. In some industries, formal 3D model reviews are conducted at various stages of the design.

Specifications can also be generated for the cognitive elements of a design, such as whether a Human System Interface (HSI) enables users to complete tasks effectively and efficiently. This specification will include how information is presented to the users and how users control the system. In a control room (e.g., on a nuclear power plant, a railway signalling centre, in air traffic control, or electricity distribution centre), such requirements of the control interface will be key to safety.

These cognitive elements address mental processes such as perception, memory, reasoning, mental workload and decision making.

The investigation into a major explosion at the Milford Haven oil refinery (24 July 1994) concluded that the control room operators missed key information that could have prevented the event. It also found that in the 11 minutes prior to the explosion, the two operators had to recognise, acknowledge and act on 275 alarms. Clearly, they were set up to fail.

A specification for the design of a new control room would include the number of alarms that could be presented to staff during normal operation and during emergency situations. The purpose of this specification is to prevent such alarm overload. In other words, the control room design specification would provide a standard that takes human (information processing) limitations into account.

Whereas a physical specification often provides numerical dimensions (widths, heights etc.), a cognitive specification may consist of a set of guiding principles. For example, in the case of an alarm system, it may include the following principles:

• All alarms should have a well-defined operator response
• Alarms from out of service equipment should be suppressed
• Define prioritisation rules and apply them consistently to each alarm in every system
• Prioritise alarms proportionately, e.g., 5% high priority, 15% medium, and 80% low
• The long-term average alarm rate during normal operation should be no more than one every ten minutes.

Example human factors standards

There are a large number of international and national standards that address human factors. These may be used to create a company HFE standard, or a HFE specification for a particular project.

For the design of a high-hazard facility (such as an oil refinery or a nuclear power plant), relevant international standards include the following, which address both the physical and cognitive requirements:

• ISO 15534-1, Principles for determining the dimensions for openings for whole-body access into machinery
• ISO 14122-2, Safety of machinery: Permanent means of access to machinery – Part 2: Walking platforms and walkways
• ISO 14122-3, Safety of machinery: Permanent means of access to machinery – Part 3: Stairs, stepladders and guard-rails
• ISO 14122-4, Safety of machinery: Permanent means of access to machinery – Part 4: Fixed ladders
• ISO 11064, (Parts 1 to 7) Ergonomic design of control centres.

National standards include:

• Norwegian NORSOK C-001, Living quarters area
• Australian AS 1657, Fixed platforms, walkways, stairways and ladders: Design, construction and installation.

And those produced by industry associations include:

• ASTM F1166, Standard Practice for human engineering design for marine systems, equipment, and facilities, American Society for Testing and Materials (ASTM)
• Publication 191, Alarm systems: A guide to design, management and procurement, The Engineering Equipment and Materials Users’ Association (EEMUA)
• Publication 201, Control rooms: a guide to their specification, design, commissioning and operation, The Engineering Equipment and Materials Users’ Association (EEMUA)
• NUREG-0700 (Rev.3), Human-system interface design review guidelines, U.S. Nuclear Regulatory Commission, July 2020.

Many of these standards are priced publications, and so unfortunately I cannot provide copies here. Those working within large companies or engineering contractors will have access to these standards via their library or information centre. To illustrate the contents of a HFE specification, I have outlined two examples below that can be obtained at no cost.

What else informs a HFE specification?

In developing a company or project HFE specification, you may wish to include requirements that address recent incidents or near-misses. You could also involve the workforce to gain an understanding of what works and what doesn’t with your existing products or facilities. An understanding of the tasks performed by end users will inform what aspects require detailed human factors requirements. For example, knowing what controls and displays they need, what type of alarms would be necessary etc., will inform the key sections of a HFE specification.

As always, the context is also important. The design specification for controls that are operated in a cold environment (where the operator is wearing thick gloves) would be quite different to a specification for controls in warmer indoor environments.

An understanding of the technology to be used in the design will also be helpful. There would be little value in creating detailed specifications for physical push-buttons, rotary switches and toggle switches if the design will be adopting soft controls via a touchscreen. Similarly, there’s little value in creating a detailed specification for stairs, if the facility is on a single level.

Example HFE specifications

A publication by the UK Energy Institute (February 2024) is freely available, and this provides key design requirements for nine areas in the early phases of a facility design. It is applicable to oil and gas facilities, as well as renewable energy sectors, but will be helpful for other industries. The document focusses on the physical layout issues (anthropometrics), rather than cognitive design issues.

The nine areas addressed in this human factors design standard include walkways, ladders, stairways, wash stations, common hazards, valves, lifting areas, and aspects of accommodation and control rooms. This publication is based upon several existing standards, including those listed above. Helpfully, these standards are referenced in the text and so you can see where a particular requirement originated.

An example diagram from the UK Energy Institute document is provided below. See here for the full publication (available free of charge). This is an excellent resource with plenty of diagrams to help explain the requirements. If you are developing an in-house human factors standard for your major projects, this would be a good starting point.

In relation to the cognitive issues, a freely available publication from the U.S. Nuclear Regulatory Commission provides a huge amount of detail (NUREG-0700 Rev.3, 2020). This document provides extensive guidance on the design of the characteristics of Human-System Interfaces (HSIs) on nuclear power plants (although much is relevant to other industries). It also provides guidance on physical requirements.

Human-System Interfaces are the parts of a nuclear power plant with which personnel interact in performing their activities, such as alarms, information displays, and controls.

This guidance will enable the development of HSIs (sometimes called Human Machine Interfaces, HMIs) that support cognitive activities such as information processing and decision making.

NUREG-0700 also addresses the design of workplaces and workstations, as well as the environmental conditions in which these interfaces are used (including temperature, humidity, ventilation, illumination, and noise). It’s very thorough, extending to over 500 pages. Although designed for use in a particular industry, it’s a useful reference for anyone studying human factors to gain an appreciation of how design influences human performance.

Example guidelines from NUREG-0700 include the following:

The benefits of a HFE specification

These specifications are based on sound human factors principles: in other words, they have been developed using what we know of the physical and mental capabilities of end users. By adopting these specifications, your designs will set people up to succeed. This will have a range of benefits including safety, reliability, quality and productivity.

If your standard is used company-wide, this will create a consistent environment across all facilities or equipment, reducing the potential for confusion. Anyone that has driven an unfamiliar vehicle with the turn indicators on the opposite side to what you are used to will recognise the value of consistency in design.

Providing all potential suppliers or contractors with your company’s human factors specification will enable them to provide a more accurate quotation for the build – and, in theory, will enable them to create a ‘right-first-time’ design that complies with your requirements. These HFE specifications provide clarity and can prevent a great deal of re-work. Remember that changes are easier to make on paper early in the design, rather than in reality once something has been built.

In addition to checking the human factors specification during 3D model reviews, these criteria will also be invaluable when verifying the facility once it has been built. Before the facility is handed over to the customer, all key dimensions can be checked to ensure that the design on paper has been translated into reality. For floating oil and gas facilities, this may involve an inspection of the facility in the shipyard where it is under construction. The HFE specification can be modified into a checklist, and the HFE specialist will walk around the vessel checking every item of equipment and every access way to ensure compliance with the specification.

Applying a human factors engineering specification will translate good design principles into reality.

Further reading

Human factors standards for facility design: Early design quick reference guide, Energy Institute, London, February 2024. This free publication summarises the key design requirements and considerations as described by commonly used human factors design standards and common industry good practice. It covers nine areas of facility design, covering walkways, ladders, stairways, wash stations, common hazards such as hot and cold surfaces, valves, lifting areas, and aspects of accommodation and control rooms.

Human-System Interface Design Review Guidelines, NUREG-0700 Rev.3, U.S. Nuclear Regulatory Commission, July 2020. This extensive document (563 pages) provides detailed guidelines that address the physical and functional characteristics of Human-System Interfaces (HSIs). HSIs are the parts of a nuclear power plant with which personnel interact in performing their functions and tasks. This document addresses visual displays, menus, controls, alarms, automation, workstations and workplaces.