Analysis, and consequences of failures;
•Reduction of frequency and mitigation of the consequences of failures;
•Cost of reducing risks;
•Damage limitation and its value.
The U.S. Air Force initiated a program called Integrated Computer Aided Manufacturing (ICAM) in the 1970s. They developed a simple tool to communicate this program to technical and non-technical staff, named ICAM-DEFinition or IDEF methodology1,2. With IDEF, we use a graphical representation of a system using activity boxes to show what is expected of the system. Lines leading to and from these boxes show the inputs, outputs, controls, and equipment.
As an illustration, consider a simple pencil. What do we expect from it?
Let us use a few sentences to describe our expectations.
A.To be able to draw lines on plain paper.
B.To be able to renew the writing tip when it gets worn.
C.To be able to hold it in your hand comfortably while writing.
D.To be able to erase its markings with a suitable device (eraser).
E.To be light and portable, and to fit in your shirt pocket.
The item must fulfill these functional requirements or you, the customer, will not be satisfied. If any of the requirements are not met, it has failed. Figure 2.1 illustrates a functional block diagram (FBD) of how we represent the second function in a block diagram.
Figure 2.1 FBD of pencil system.
Note that we state our requirements in the most general way possible. Thus, pencil does not have to be a graphite core held in a wooden stock. Pencil can easily be a metal holder, and still meet our requirements. The second function is met whether we have a retractable core or if we have to shave the wood around the core.It could have a hexagonal or circular section, but must be comfortable to hold. The writing medium cannot be ink, as it has to be erasable. Finally, its dimensions and weight are limited by the need for comfort and size of your shirt pocket!
Every production or distribution process has several systems, each with its own function, as illustrated by the following examples.
•A steam power-generation plant has a steam-raising system, a power generation system, a water treatment system, a cooling system, a control and monitoring system, and a fire protection system.
•A courier service has a collection and delivery system, a storage and handling system, a transport system, a recording and tracking system, and an invoicing system.
•An offshore oil and gas production platform has a hydrocarbon production system, an export system, a power generation system, a communication system, a fire and gas protection system, a relief and blow-down system, an emergency shutdown system, and a personnel evacuation system.
•A pizza business with a home delivery service has a purchasing system, a food preparation system, a communication system, and a delivery system. Sometimes, all these systems may involve just one person, who is the owner-cook-buyer-delivery agent!
We can use functional descriptions at any level in an organization. For example, we can define the function of a single item of equipment. Jones3 illustrates how this works, using the example of a bicycle, which has the following sub-systems:
•Support structure, e.g., the seat and frame;
•Power transmission, e.g., pedals, sprockets, and drive chain;
•Traction, e.g., wheels and tires;
•Steering, e.g., handles and steering column;
•Braking, e.g., brakes, brake levers, and cables;
•Lighting, e.g., dynamo, front and back lights, and cables.
We can define the function of each sub-system. For example, the power transmission system has the following functions:
•Transfer forces applied by rider to drive-sprocket;
•Apply forces on chain;
•Transmit the force to driven-sprocket to produce torque on rear wheel.
Similarly, we can examine the other sub-systems and define their functions. The functional failure is then easy to define, being the opposite of the function description; in this case, fails to transfer force.
2.2 FUNCTIONAL BLOCK DIAGRAMS (FBD)
These systems and sub-systems below them are aligned to meet the overall objectives. An FBD provides an effective way to demonstrate how this works. It illustrates the relationship between the main function and those of the supporting systems or sub-systems.
We describe the functions in each of the rectangular blocks. On the left side are the inputs—raw materials, energy and utilities,or services. On the top we have the systems, mechanisms, or regulations that control the process. The outputs, such as intermediate (or finished) products or signals, are on the right of the block. Below each block, we can see the means used to achieve the function; for example, the hardware or facilities used to do the work. As a result of this approach, we move away from the traditional focus on equipment and how they work, to their role or what they have to achieve.
In the example of the pencil that we discussed earlier, let us examine failure of the third function, that is,
•It is too thin or fat to hold, or
•It has a cross-section that is irregular or difficult to grip,
•It is too short.
We then break down the main function into sub-functions. In the case of the pizza business, the sub-functions would be as follows:
•A purchasing system that will ensure that raw materials are fresh (for example, by arranging that meat and produce are purchased daily);
•A food preparation system suitable for making consistently high quality pizzas within 10 minutes of order;
•A communication system that will ensure voice contact with key staff, customers, and suppliers during working hours;
•A delivery system that will enable customers within a range of 10 km to receive their hot pizzas from pleasant agents within 30 minutes of placing the orders.
Each of the sub-functions can now be broken down, and we take the delivery system as an example:
•To deliver up to 60 hot (50–55°C) pizzas per hour during non-peak hours, and up to 120 hot pizzas per hour from 5:30 p.m. to 8:00 p.m.;
•To
