Some years back my boss, former chief engineer and surveyor, an engineer colleague and myself, were travelling to a meeting. My boss asked our colleague to fix a screen and the latter went through the manual to see the way to mount it, till we’ve reached our destination and our boss took the screen and fit it. No manual, just noticing the connection points.
It is interesting to see how much of this practical approach is governing ships, a predominantly empirical science. In my last post I’ve been dwelling on theories of storing hydrogen and explosive gases onboard. Yet presently yachts have low flash fuel onboard, introducing explosive atmospheres, either in portable canisters or inside the tanks of tenders and jet skis. Accommodating such fuels in our yachts is standard and there are regulations defining the parameters, but with a twist.
As per electrical standard ISO-60079, integrated or referred to in the classification regulations, we have three zones depending on the categorisation of explosive atmosphere, reflecting the hazard under normal operation conditions.
Zone 0 where there is a continuous, persistent presence of explosive atmosphere and respective risk. This is for example a space like the low flash fuel tank itself and attached piping containing low flash fuel;
Zone 1 where there is an occasional presence of flammable gases, mist or vapour that are mixed with air. These are mostly areas around ventilation outlets from Zone 0 or spaces containing piping and structure of Zone 0 without ventilation, captured in spheres;
Zone 2 is the zone where it is unlikely to have flammable gases, mist or vapour and if it appears it will be for a very limited time. Depending on the source it is also defined by spheres of various diameters;
Yet in yachts and their tender/ toys garage we are not going through aforementioned detailed review of these areas, possible release points and spheres. We have a prescribed requirements of ventilation for the space (6 air changes per hour of the empty space) and defined the hazardous area of 450mm above the deck that needs electrical equipment certified safe for petrol vapours.
This a very interesting deviation from the electrical standard, which one could assume has been borne from experience. The release gases will be hydrocarbons, something like butane, which are heavier that air and will rest close to the ground. It is hard to pin point the exact location of the jet ski during the various operation and life of the yacht. Tenders change, toys get renewed, often get larger, pin pointing the escape connection will have a very short timeframe and will necessitate management to review this arrangement frequently. So going into the practical approach, selecting the hazardous area all across the space close to the deck and adding EX-rated equipment there simply makes sense. Owner’s can enjoy their investment and authorities apply measures to protect the yacht and crew.
It is often argued that we engineers can get lost in our heads, do we need to adopt a more “go to” attitude? There are many advocates of trial and error, from every failure you discover a way that is not working. Benjamin Franklin was the modern founder of this approach and definitely favoured us with his inventions. Yet there are risks attached to this approach and many have paid a very hard price for it. A fusion of theories and praxis is best, because procrastinating never produces results, while cautious experimenting can support development.