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Control room design

This Technical Measures Document refers to codes, standards and best practice applicable to the design of control rooms.

Related Technical Measures Documents are:

The relevant Level 2 Criteria are:

General principles

There are two major aspects of control room design that should be taken into account in the Safety Report these are:

Control room structure

For large plants, control rooms are likely to be situated in separate buildings away from the process plant which they serve. For medium or small plants control rooms may be within the plant building or control panels may be located local to the plant. Whatever the location, control rooms should be designed to ensure that the risks to the occupants of the control room are within acceptable limits and that it is suitable for the purposes of maintaining plant control, should the emergency response plan require it, following any foreseeable, undesirable event within the plant.

Events that may affect the control room are:

The threat from explosions and pressure bursts should be considered in the structural design of control building. A methodology for this is presented in the recent CIA/CISHEC guidance CIA Guidance for the location and design of occupied building on chemical manufacturing sites. This considers the vulnerability of the building to possible overpressures associated with particular events. Buildings should be designed to withstand an overpressure that will ensure that risks to individuals within the building are below acceptable limits. Particular attention should be given to the provision of windows, the presence of heavy equipment on roofs (e.g. air conditioners) and the ability of internal fixtures to withstand the building shaking. If windows are present, consideration should be given to the use of laminated or polycarbonate glass, to prevent serious injury to occupiers of the control room in the event of an overpressure. ALARP principles should be applied in these considerations and cost benefit used to determine if additional measures should be applied.

In consideration of toxic gas releases the control room should provide a safe haven for its occupants. This will include arranging that the building is adequately sealed to prevent ingress of gases to levels of concentration that will affect the health and thereby the ability of the operators to maintain control of the plant. Careful consideration of the building ventilation system is required to ensure that air intakes are situated away from areas that may be affected or to arrange that there is no air intake during an incident, preferably by closure of an automatic valve linked to a gas analyser.

Measures for protection from fires should ensure the control room will withstand thermal radiation effects without collapse and that smoke ingress is controlled. Materials of construction should be fire resistant for the duration of any possible fire event. Smoke ingress may be controlled in a similar manner to toxic gas ingress.

Each of these methodologies should be applied to control rooms within buildings as well as separate control buildings. Control panels on the plant itself cannot be so easily be protected, therefore diversity and redundancy should be applied to ensure that plant control can be maintained in an emergency. Risk Assessments should be undertaken to demonstrate that primary and secondary (domino) risks are within acceptable limits.

Human factors/ergonomics

Operators should be able to demonstrate that appropriate human factors considerations have been given to the design, commissioning, and operation of control rooms under both normal and abnormal plant operating conditions to reduce the frequency of human error due to control room deficiencies.

It is vitally important that a control room and its operators are considered as a whole system and not in isolation of each other. For example a well designed control room for use by 4 operators is dangerous when staffed by 3 operators. Similarly, the best-trained operators cannot guarantee high reliability in a poorly designed control room.

Factors to be taken in account are included on the following paragraphs.

Environmental issues

Layout

Maintenance

Thermal environment

Visual environment

Lighting should be such that it does not create veiling reflections on VDUs or other reflective surfaces that require monitoring.

The type of lighting should be adequate for the task. i.e. for office work a lux (lux is the unit of illuminance - measured using a light meter at the work surface) figure of between 500 - 800 is suggested.

There should be no perceptible flicker from strip lighting.

It is desirable to provide adjustable lighting for control rooms that are manned 24 hours a day. During night-time operation lighting is often dimmed.

Windows in control rooms should not cause veiling reflections on reflective surfaces. Adequate means of blocking out direct sunlight should be provided.

Auditory environment

The average noise level within the control room shall not exceed 85 dB(A) during the length of the working day.

For office work a noise level below 40 dB(A) is not desirable as it can cause interference between operators.

Prolonged, very low or very high frequency noises should be avoided.

Noise levels should not interfere with communications, warning signals, mental performance (i.e. be distracting).

Man Machine Interface (MMI)

For mental workload, conditions of over and under-arousal should be avoided. The duration of tasks that have an associated low or high level of mental workload should be limited. Both these extremes will increase the likelihood of human error affecting the system. The design of the MMI should be based on a full Task Analysis.

An interface should provide the operator with the general following information:

Alarms

Coding techniques

Designing displays

Text

Labels

Display devices

Graphics

Method Advantage Disadvantage
Numeric
  • Accurate quantitative information
  • Quickly read
  • Cannot illustrate rate of change or approach to limit
  • Rapidly changing data is unreadable
  • Difficult to locate individual data items if presented in a list or table.
Bar charts/analogue dials
  • Easy to check whether data is within limits
  • Possible to mark alarm limits
  • Displays rate of change well.
  • Easily compared to other similarly presented data.
  • Provides at a glance appreciation of operating conditions
  • Movement can potentially distract operators.
  • Slow read time.
  • Inaccurate if numerical value has to be derived.
Pictorial displays
  • Ideal for showing plant configurations.
  • Can improve operator situational awareness of plant.
  • Operator’s mental model of the plant may differ from the mimic.
  • Can be very difficult to learn.
Trend displays
  • Ideal for presenting continuously changing information.
  • Presents rate of change in an easily understood format.
  • Good for comparing data plots
  • Provides historical data over time
  • Inaccurate if numerical value has to be derived.
  • Only four parameters can be displayed

Controls

Control operation Push- button Foot- switch Toggle switch Rocker switch Rotary selector Knob Slider Joystick Thumb- wheel Crank Hand- wheel Lever Pedal (pivot) Pedal (thrust)

Discrete - Activate on/off

G

G

VG

VG

P

·

P

·

·

 

·

·

·

·

Discrete - Select three states

A

·

F

P

VG

 

 

 

 

 

 

G

 

 

Discrete - Select multistate

A

·

P

 

VG

 

VG

 

F

 

 

G

 

 

Continuous - Set/adjust

 

 

 

 

 

VG

G

 

F

VG

G

G

 

 

Continuous - Control/track

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Exert Force

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Speed of operation

VG

F

VG

VG

F

F

G

G

P

 

 

 

 

 

Inherent visual feedback

P

 

 

 

 

 

 

 

 

 

 

 

 

 

Anthropometry

Reach

Seating

Posture

International Codes of Practice

Further reading

Mecklenburgh, J.C., ‘Process plant layout’, George Godwin, 1985.

Ball, P.W. Ed, ‘The guide to reducing human error in process operations’, The Human Factors In Reliability Group, The SRD Association, 1991.

Pheasant, S., ‘Bodyspace - anthropometry, ergonomics and the design of work’, Taylor & Francis, London, 1996.

Oborne, D. J., ‘Ergonomics at work’, Second Edition, Wiley, New York, 1989.

Corlett, E. N. and Clark, T. S., ‘The ergonomics of workspaces and machines - A design manual’, Second Edition, Taylor & Francis, London, 1995.

Case studies illustrating the importance of Control room design

2016-07-22