This fine, highly flammable mist of between 1 and 10µm is produced at surface temperatures of between 200°C and 600°C, while droplets greater than 50µm are typically produced from pinhole leaks in a pressure line.
In an open machinery space, oil mist or spray of any droplet size must be treated as a potential fire risk and appropriate detection systems should be in place to safeguard ships’ crew and equipment before it becomes a MAIB incident.
The principle used in the early oil mist detection systems – obscuration light absorption – is still used by most manufacturers of oil mist detection systems to this day. The technology involves the extraction of the oil mist from selected points within the crankcase which is then transferred in sequence via discrete pipes to a central detector, usually mounted on the engine, with a facility for remote reading at a centralised panel.
However, these systems have a very slow response time which, in some cases, raises alarm after engine seizure or explosion has actually taken place.
When the lenses become obscured a false alarm can occur.