In this context 'competent' means they have the knowledge and expertise in relation to the equipment concerned. These people should know their own limitations and not be expected to understand everything. If they are presented with a particular issue outside their field of knowledge they should seek the opinion of someone more suitably qualified. Independent' in this respect means that they should not normally inspect their own work or anything with which they have been closely involved. It is important that all equipment that has any bearing on safety is designed and properly constructed so as to be fit for its intended purpose.
Most equipment is designed to well-proven standards and established practice.
The design and construction of any equipment that departs from these established practices should be assessed to make sure that its safe operation is not impaired. It is recommended that anyone who publishes a design, checks that the design is safe. Supporting information should be available. Designs are preferably checked before manufacture. Any steam-powered model should undergo and pass an appropriate boiler testing procedure.