Human Factors Engineering (HFE) is the process of integrating human capabilities, limitations, requirements and expectations in the design of products, workplaces or work systems (plant / facility) resulting in the effective, efficient, safe and healthy functioning of human beings, thereby improving operations and maintenance task performance. The benefits identified relate both to business (economics) and to working conditions, resulting in a reduction of the life cycle costs of a facility.
Failing to apply Human Factors Engineering (HFE) principles during the design of plant or equipment can result in manual valves (or other items that a person has to operate, view or maintain) being located in a position that is difficult or dangerous for the person to access.
This has several consequences:
Due to space constraints and the complexity of modern chemical, process or nuclear power plants, not every valve or instrument that people will interact with can be positioned at the ideal location for human interaction. So, if compromises have to be made, how do we ensure that they are the best compromises for safety and operability? And how do we justify those compromises to our stakeholders?
This is where Valve Criticality Analysis comes into place. VCA is a structured approach that considers the importance of each valve and its placement. It is often used in the oil, gas, nuclear, marine and defense industries taking into account Human Factor Engineering for the placement and classification of valves.
Valve Criticality Analysis provides structure to the decisions that determine the location and accessibility of valves.
The aim of VCA is to:
This will improve safety, operability and maintainability when operating these valves. Although the focus tends to be on “valves”, the approach is equally suited to reviewing the location and access to instrumentation or other equipment that people interact with.
In VCA, each valve is assigned a criticality rating which then informs its access requirements (i.e. those valves that are critical to operations or safety, and those that are accessed most frequently, should be easy to access and operate).
VCA is typically applied in the Front-End Engineering and Design (FEED) and Detailed Design phases of a major project, or as soon as initial layouts are available.
Key inputs to Valve Criticality Analysis are a good understanding of the tasks that people are required to perform, (in normal operations and in emergency situations), as well as an understanding of the capabilities and limitations of the people who will perform these tasks.
Valves are typically placed into one of three categories:
|Valve criticality category
|Category 1 (C-1) Valves
Relief valves and depressuring valves
Trip and anti-surge control valves
Emergency shutdown valves
Liquid cargo transfer valves Tie-in Valves
|Category 2 (C-2) Valves
|Condensate drain valves
Service oil valves
Hydraulic service valves
Potable water valves
Manual valves for normal startup/shutdown
|Category 3 (C-3) Valves
|Valves used for commissioning
Valves used for decommissioning
Valves used to isolate tanks for inspections
Valves for pressure tests
Valves used in dry dock only
The lower the criticality rating, the more freedom that a designer has in determining the layout and access requirements. Based on the Company’s standard HFE, the access and positioning requirements for each Category of valve should be clearly specified, along with the clearances around each Category of valve, labelling requirements, maximum forces required to operate etc. For example, Category 1 valves should be placed at waist/chest height, rather than below the knees or above the shoulders
The lower the criticality rating, the more freedom that a designer has in determining the layout and access requirements. Based on the Company’s standard HFE, the access and positioning requirements for each Category of valve should be clearly specified, along with the clearances around each Category of valve, labelling requirements, maximum forces required to operate etc. For example, Category 1 valves should be placed at waist/chest height, rather than below the knees or above the shoulders.
The following approach is usually undertaken as a small workshop with a team of operations, maintenance and safety personnel; chaired by a human factors specialist if available. On a large project, the design may be divided into sections and a series of VCA workshops may be required.
For large scale projects, where it may not be possible for detailed review of all valves and equipment by a human factors professional, training should be provided to design teams so that they understand the principles of VCA and know when to raise concerns with a human factors professional.