When boilers were first made for steam engines, little was known about steel. Plates were riveted together and engineers were ignorant of the stresses in the material. Of course there were successes and there were failures; both can be learned from, even if the lessons are only 'use thicker steel plates'. Later it became possible to weld plates, and new lessons had to be learned.
All this accumulated experience is brought together into a 'standard'. The standard will dictate critical features of the design, construction methods and safety testing of pressure vessels. For example it will guide the designer in relating wall thickness to diameter and pressure. For the ammonia vessel I described in the previous section, the standard specifies that the plate would have to be 150 mm thick. Then permitted types of steel and the welding methods will be specified. Finally the whole thing has to be tested to beyond its working pressure.
Standards govern the design and construction of virtually everything which carries any safety implications. Any company that transgresses the standards, and whose product is then responsible for an accident, will find itself in serious trouble. For the moment though it is interesting to contemplate the apparent conflict between opportunities for innovation and the requirement to adhere to standards. As standards derive from past practice, they are apparently not conducive to innovation. What is the way out of this dilemma? In reality standards are revised, amended, and superseded to account for changes in knowledge and practice.
You can look around your home to try to find evidence of this – you should find the phrase 'Conforms to BS xxxx ' (the BS standing for 'British Standard', and the xxxx being a number) or similar. Electrical goods, or their packaging or instruction manuals, would be a good place to search. For example, I found in the instructions for a French-made electric kettle that its moulded-onto-the-wire mains plug conformed to BS 1363 and that only fuses approved to BS 1362 should be used as replacements. Furthermore the kettle was constructed to comply with the radio interference requirements of EEC directive 87/308/EEC. I have also noticed the number BS EN 228 (where the EN indicates that the standard is applicable throughout Europe, not just in the UK) on fuel pumps for unleaded petrol. These last two regulations appear to control the function or composition of the product rather than its safety.
Activity 8 (self-assessment)
Which of the following list would you put into the categories of one-off production, mass production, and bulk production?
- a.A modern 3-bedroom house on a development of 30 houses.
- b.Liquid oxygen for a chemical laboratory.
- c.A USB flash drive.
- d.A Blu-ray Disc of a movie.
- e.The Channel Tunnel.
- f.A photocopier.
- g.Garden compost.
- h.Car tyres.
- i.A hand-made paperweight.
- a.A modern 3-bedroom house on a development of 30 houses is a one-off (no economy of scale here).
- b.Liquid oxygen for a chemical laboratory is produced in bulk.
- c.A USB flash drive is mass produced.
- d.A Blu-ray Disc is mass produced.
- e.The Channel Tunnel is a one-off.
- f.A photocopier is mass produced.
- g.Garden compost is produced in bulk.
- h.Car tyres are mass produced.
- i.A hand-made paperweight is a one-off.