Working by numbers
by Bernard McGrath, Inspection Validation Centre

I know that 42 is the answer but as I haven't read A Hitchhiker's Guide to the Galaxy, I had to consult my esteemed colleagues to clarify what the question was. Evidently it is life, the universe and everything. If only that was the only number we had to bother with. It seems that numbers are taking over our lives.

At one time I only had to remember one telephone number and that was only four digits and three letters long. Now, everybody in a family has a mobile consisting of 11 digits. With chip and pin there is another sequence of numbers to remember for every bank card you hold. If you use the cards over the phone, not only do you have to give the number on the front but you now have to add another group from the rear. Then there are all the numerical security pads on doors that you have to remember.

Other numbers carry a greater level of significance. Major events are given numerical tags: 9/11 and 7/7. We all hope for the life-changing lottery numbers to be picked out. Unless you buy a lucky dip, it is likely that the numbers you select will mean something personal to you: an age, a house number, the day of a month of a birthday etc.

Individual numbers appear frequently. For those of you who predate the 1970s, 12 was particularly prevalent as a measurement unit: 12 pence in 1 shilling, 12 inches in a foot and 12 of anything in a dozen. With decimalisation, 12 was ousted in preference of 10 which became the base of all measurements. 10 is a nice round number which makes it convenient for other uses such as the amount of discount to give on sales, the percentage sample to audit or the number of points to deduct from a club going into administration! The development of computers has promoted the cause of 2 and 8 through the use of binary and hexadecimal numbers.

NDT has its own special numbers as well. 58 appears frequently these days in reference to the reliability of manual ultrasonics. However, the manual ultrasonic equivalent to the Hitchhiker's 42 is 3. Reliable detection is often claimed for 3 mm and above. 3 mm is the size given to defects too small to be sized. ±3 mm is frequently quoted as the sizing error. Three is also a key number in many natural and social systems. The fire triangle is made up of oxygen, fuel and heat. Environmental cracking has a similar triangular requirement in stress, environment and susceptible material. The three circles model of leadership has task, team and individual.

The latter is similar to the Health and Safety Executive's (HSE) model of human factors which expresses the need to address issues relating to the job, the individual and the organisation in order to reduce errors and improve performance. However, if we look to apply this model to NDT operator performance, then some limitations become apparent. There is no problem with the individual, which obviously is the operator. The job is a little less well-defined. Some of what could be assigned to the job, such as preparation and aspects of the environment, could just as easily be covered by the organisation.

The organisation nominally covers such things as planning, safety, management and culture. But what falls under the organisation umbrella is not well-defined. Organisation can mean different things to different people and with the lack of any clear definition of what it entails comes a blurring of the lines of responsibility. Who is responsible for ensuring the correct organisation of any inspection task?

In order to maintain the simple triangular model of NDT operator performance, and avoid having to move to a polygon, a substitute for 'organisation' needs to be found. Whatever label is given, it needs to be supported by an agreed definition of what constitutes that leg of the model. A role to manage this leg should be assigned to an individual or team and responsibilities clearly defined. Only then can we be confident of reducing errors and improving performance.

Until then, when it comes to the reliability of NDT, we may not know the precise answer but at least we know that the answer is not a single number 1. It may even be as high as 58.

Please note that the views expressed in this column are the author’s own personal ramblings for the purpose of encouraging discussion within the NDT Newspaper. They do not represent the views of the IVC, Serco Assurance or the HSE who funded the PANI projects.

Letters can be mailed to The Editor, NDT News, 1 Spencer Parade, Northampton NN1 5AA. Fax: 01604 231489; E-mail: ndtnews@bindt.org
or e-mail Bernard McGrath direct at Bernard.McGrath@sercoassurance.com