Monday, 17 November 2014

Fire Protection and High Speed Crafts

Safety against fire aboard ships is a major area of concern for seafarers and designers. Especially when it comes to high speed vessels, which are generally smaller in size and are prone to maximum and critical damage within no time in absence of fire protection systems. This has become an area of research and regular assessment of regulations are being done to minimize both human and material loss from such incidents. You definitely do not want to be a passenger on the receiving end on a ship when it catches fire.

Fig.1: A burning Yacht at Sydney Harbour
(Courtesy: )

No wonder these regulations are put forward under the SOLAS (International Convention for the Safety of Life at Sea) treaty by deliberations at International level for which it is quite important among the international treaties relating to merchant ship safety at sea. SOLAS actually specifies minimum standards for the equipment in use and mode of operation which are part responsibility of Flag States to monitor. Classification societies have set up rules and regulations for such Vessels, IMO has its own. The Indian Register of Shipping calls them: Rules and Regulations for the Construction and Classification of High Speed Crafts and Light Crafts.

Fig.2: The SOLAS treaty 
sees to the safety of vessels
on an International Level
High speed crafts are of light displacements and they generally use unconventional; shipbuilding materials like fibre reinforced plastics, aluminium alloys and the like (I hope you are familiar with the luxury yachts of today which look faster and prettier than their ancestors), but to distinguish them from conventional crafts in a more technical manner, the speed and volumetric Froude number are often the factors for applying regulations. When designing ships, you should see to it that your vessel has some quick (I mean really quickly) fire detection system, people should be able to find fire extinguishing devices and evacuation routes (and alternate routes) in case of emergencies. It is often observed in such situations that panic clouds our reason.

Let us talk about some points in general about to these High Speed Crafts. Generally such details in design like the presence of ventilation systems and their control, fire resisting divisions are submitted in a general arrangement plan in detail even to particulars of surface lamination (if used somewhere). The important thing about these measures which are somewhat similar to those for larger vessels is that the fire protection time or the time period till which you expect the ship to sustain damage till structural failure occurs.

Division of ship based on level of hazard

You should identify certain parts of the vessel according to the extent of damage in the event of a fire. Such divisions are usually called:

  • Areas of Major Fire Hazard – Mainly has to do with areas of the ship containing flammable liquids, places of certain deck area selling flammable liquids like alcohol, kitchen areas (galleys). Engine rooms of ships, especially Internal Combustion Engines, are considered along with other machinery spaces. Like I mentioned, passengers are not allowed in some of these areas except when accompanied by some fire safety crew.

Fig.3: Certain parts of a boat like the galleys (kitchens) and others spaces having flammable fluids are classified as Major Fire Hazard Areas based on their deck area.
(Courtesy: Dubois Naval Architects )
  • Areas of Moderate Fire Hazard – These include spaces for crew accommodation other than sleeping, stores on board containing alcoholic beverages. Shops not selling flammable items, etc.
  • Areas of Minor Fire Hazard – These are areas like tanks, empty spaces, areas open to the public exposed to low or no fire risk, areas for refreshment and certain cargo and machinery spaces.
Certain spaces like those with equipment for navigation, battery systems and main electronic control systems are also considered separately.

Separation of Accommodation Spaces from Remainder of Ship based on such hazards

Fig.4: It is very important to 
isolate accommodation spaces
 for passengers and crew 
from potential zones.
( )
It is necessary to ensure that the passenger spaces have been Passengers are not allowed to go to vehicle spaces and Ro-Ro spaces during voyage, and for that reason, even cargo spaces.

Certain parts of the ship have the decks and bulkheads constructed from non-combustible or fire resisting material in such a way that the temperature on the unexposed end will not rise beyond a certain limit. 

You have to see that these 'Fire Resisting Divisions' are designed structurally in such a way that they will not fail or allow smoke or flames to pass until the end of a certain fire protection time depending on the level of hazard I spoke about earlier. Even your gaps for ventilation in entrances of public toilets need to be positioned towards the lower part of the door (guess why?).

Based on the above analogy, the materials used in the subdivisions of a ship are categorized into three main types, namely:

"A" Class Divisions: For a division to be certified as "A" Class, it has to limit the average temperature on the other side (the side opposite to which it is exposed to fire) to a maximum of 140 degree Celsius and the maximum temperature at any point on the other side to 180 degree Celsius, up to a certain time. Now based on this time up to which the material limits the above temperatures, "A" Class divisions are subdivided into four types:

  1. A-60: This type of "A" Class division can limit the temperatures up to maximum 60 minutes.
  2. A-30: This type of "A" Class division can limit the temperatures up to maximum 30 minutes.
  3. A-15: This type of "A" Class division can limit the temperatures up to maximum 15 minutes.
  4. A-0: This type of "A" Class division cannot limit the temperatures beyond 60 seconds.
"B" Class Divisions: A division is certified as "B" Class when it limits the average temperature on the other side to 140 degree Celsius and the temperature of any point on the other side to 225 degree Celsius up to a time limit depending upon the following three sub-types:

  1. B-15: Can limit the temperatures up to maximum 15 minutes.
  2. B-0: Cannot limit the temperatures beyond 60 seconds.
"C" Class Divisions: For a division to be classified as "C" Class, it has no fixed temperature limits, but certainly needs to be certified by the classification societies.

Restricting use of combustible materials as much as possible

Fig.5: Decks and bulkheads should ideally be
constructed using non-combustible materials,
sometimes another layer of material does the trick
( )
The separating divisions in the ship like the ceilings which are not a part of the fire resisting divisions are necessarily of the non-combustible type. They may restrict fire too which is desirable in the event of a mishap. All exposed surfaces on the vessel like the public spaces and accommodation are required to pass certain tests for toxicity and smoke from fire. Strict laws apply for both areas allowing/not allowing smoking. The exhaust pipes which are of valid concern are designed to minimize risk from fire and structures in contact with them which are potentially prone to risk are insulated with non-combustible materials.

You should see that fuel tanks are never placed in proximity to Major Fire Hazard Areas for reasons quite obvious. Use of fuel with flashpoint below 43oC is not allowed however it is relaxed to 35 oC for gas turbines. Tests are to be done to ensure that in event of a fire, the fire resistant divisions are able to withstand loads for a given period of time. Often tables depicting such times based on vessel characteristics are available.

Detection and containment of smoke or fire

Fig.6: Fire and smoke detection equipment
are a must have on every kind of vessel.
(Courtesy: Nordhaven)
Early detection is the key and often it is the best way to prevent huge loss from fire at an early stage itself. The areas of major and moderate fire hazard are required to be fitted with automatic smoke and fire detection systems, which of these are used depends entirely on the location of origin of fire. You would prefer putting a detector for heat in the galleys and smoke detection systems in corridors and toilets. In case of propulsive machinery, closed circuit television providing video footage are also set up. Speaking about power supply of these equipment on board, these are to have alternative power sources.
Sometimes when acoustic enclosures are used for certain spaces having gas turbines/generators, separate fire extinguishing systems need to be in place. All such machinery spaces of this sort require fire-resistant materials for containing fire. Common spaces, accessible or not, like those of bulkheads, linings of divisions, ceilings, corridors are required to have surfaces with low flame spread.

Viability of means of escape

Fig.6: Proper identification of escape routes
 does save lives and prevents excess panic
( )
Common means of escape are generally the areas of normal access to the different parts of the boat. However, it is necessary to devise alternate routes (portholes are common) for quick escape during emergency. Your plan of ladders and stairs should be such that they would provide easy access in time of an emergency, this includes considering lack of space in places with large machinery. These routes should planned in a manner such that it would be possible to escape or enter (when rescuing passenger) through these places without possibly encountering the source of fire on the way.

Availability of extinguishing devices

Fig.7: Properly spaced Extinguising equipment
of standard sizes are of great help 
during an emergency 
( )
In the event the crew or passengers are required to put out fires which sometimes block essential escape routes, portable fire extinguishing devices of appropriate mass and fire-fighting outfit are to be provided, the former especially at machinery spaces, they require regular examination and are required to be easily accessible in event of a fire. When present for control stations and similar areas involving electronic equipment, these should not contain extinguishing media which is conducting in nature. Use of fire pumps, hoses and hydrants are also common just as in our fire fighting vehicles.
The outfits for the fire-fighters are required to have excellent fire resistant properties, heat protection, water-resistance and certain electrical insulation characteristics. Often lamps (sometimes fitted on protective helmets) are required with long backup facilities. Breathing apparatus is a must with at least 30 minutes of possible usage.LSD

 Article BySudripto Khasnabis