Engine Room Space monitoring More Information below

Oil Mist Detection in the Atmosphere of the Engine Room

You may be aware, MCA and IMO, together with other Marine Societies, are very concerned about the number of fires that start in machinery room spaces. Places most at risk are engine and purifier rooms. However, other areas have their own problems and these include bowthruster rooms, steering gear and hydraulic pumps. Figures produced suggest that up to 65% of machine room fires are the result of oil mist.  

What is Oil Mist

There are two ways oil mist can be formed. One source is minute leaks in pressurized in oil lines and fittings which produced a atomized spray of oil into the atmosphere. The second source is when oil hits a very hot surface and boils.

Danger occurs when high pressure type of leaks of oil mist are formed with a particle size of 3 to 10 microns that builds up to a hazardous concentration of mist in the atmosphere. At levels of saturation conditions are truly hazardous, and if no action is taken a fire can start. The ignition temperature for this type of oil mist can be extremely low depending on the fuel that is being atomized. 

Other ways an oil mist can be generated is when drops of oil hit a hot spot or surface and boils. When oil mist is produced by boiling the particle size is then 3 to 10 microns. This mist is visible and is known as "blue smoke". The larger and hotter the hot areas is the quicker the oil mist is produced. At this stage a temperature as low as "150°C can cause ignition.

How to prevent Oil Mist fires

The ideal is to make sure no leaks occur in the first instance.  This would be simple in a perfect world, but mistakes do happen.

The practical answer is to install and Oil Mist Detection System that will detect oil mist as it is being diffused into the atmosphere which will alarm long before it saturates the atmosphere to a danger level.  It should be noted that steam and smoke have approximately the same particle size, so an oil mist detector should be able to detect these parameters, if the right system is used - which is a bonus.

Atmospheric Oil Mist Detectors

How do they work? As we represent QMI we will talk about this system. The QMI system incorporates up to 12 detectors using one Monitor. The detectors are placed around the vessel in vulnerable areas where oil mist leaks are likely to occur. The detectors are normally placed in an air stream that can normally be found by using a smoke generator. The route the oil mist usually takes is towards the turbo inlet or the exit ventilation duct. The QMI detector has a built in fan and continuously draw in and monitor the surrounding atmosphere. This is because oil mist diffuses into the environment and does not generally stay in one place.

The detector communicates with the monitor thorough a 6-core cable. The atmospheric detector heads include their own fan, this ensures correct air flow and tamper-proof operation avoiding the need to use pressure and air flow regulators. The Monitor can be stationed away from the danger area. The cable carries the signal and power to and from each detector and fan. The sensor is the same as in the QMI Multiplex crankcase detector that uses light scatter as its detection source. The monitor has alarm and activating functions with on/off switching. There is a self-diagnostic fault finding system so the monitor will not give false alarms if there is a problem with the monitor or detectors.

Concentrations of oil mist may be localized, but normally it diffuses into the surrounding area. If this concentration of oil mist spread throughout the machine room space, a flash fire can occur over a wide area

In some instances it has been known that oil mist can remain in layers if there is a strong air stream or no air turbulence. The mist then becomes a sandwich between two layers of uncontaminated air. Under these circumstances, if ignition occurs there is a quick flash fire that may leave the areas above and below the fire completely undamaged.

Oil Mist in areas where hot spots do not occur such as bowthruster rooms, purifier rooms or steering gear can have problems; for example there can be an ultimate loss of power. Oil mists in these areas are expensive as major disruption can occur, therefore, leaks should be located as soon as possible. Deposits from mists cause unnecessary mess that takes time to clean up.

An Oil Mist detection system should be considered to use along side a smoke detection system. If reliance is placed solely on a smoke detector as a form of protection against fires taking hold, a situation can arise where it may be too late to avoid damage and even loss of life.