NFPA 1405-2020 Guide for Land-Based Fire Departments That Respond to Marine Vessel Fires.
6.1 Introduction. In combating a fre aboard a vessel, fre fghters should give attention to the volume of water used for extinguishment and its effect on the stability of the vessel. Water applied to a vessel fre can jeopardize the stability of the vessel and the safety of the personnel on board. The applica‐ tion of water should be monitored carefully, and water should be removed in a timely and effcient manner. It is recommen‐ ded that the IC have a basic understanding of this chapter. However, the IC is urged to consult the vessel’s master, engi‐ neer, and other experts to determine how much water can be used safely. How and when water is added or removed from the vessel is critical. 6.2 Vessel Stability and Equilibrium. 6.2.1 General. Stability is the tendency of a foating vessel to return to an upright position when inclined from the vertical by an external force. If the vessel returns to or remains at rest after being acted upon, it is in either stable or neutral equili‐ brium. If it continues to move unchecked in reaction to the external force, it is in unstable equilibrium. An unstable vessel, therefore, is one that, after being inclined, does not fnd a point of stable or neutral stability, which is essential to maintain vessel stability and to minimize list. 6.2.2 Initial Stability. The ability of the vessel initially to resist heeling from the upright position is determined by its initial stability. The vessel’s initial stability characteristics hold true only for relatively small angles of inclination. At larger angles, defned as those over 10 degrees, the ability of the vessel to resist inclining movements is determined by its overall stability characteristics.
6.4.2 The concept of center of gravity is essentially the same for a vessel as for other mobile equipment, such as an aerial ladder. In essence, the weight of the particular piece of equip‐ ment is considered to be concentrated at that point. As an aerial ladder is raised, the unit’s center of gravity rises and the forces tending to overturn the vehicle are counteracted by the truck’s external stabilization mechanisms (also known as outrig‐ gers). Similarly, a vessel’s center of gravity also rises as weight is placed higher in the vessel. It differs from an aerial ladder in that it is unable to provide external stabilization mechanisms (outriggers) due to the water around it. 6.4.3 Vessels, therefore, suffer a loss of stability as water utilized in fre fghting accumulates above the original center of gravity. This loss is particularly signifcant with regard to vessels with large superstructures, such as passenger ships and car carriers. The higher the weight, the more detrimental is the effect. If this vulnerability is not properly understood and controlled, the consequences can impact all fre-fghting efforts severely. It is an integral part of overall strategy. 6.4.4 Free Surface Effect. Free surface, for the purpose of fre fghting, is defned as the tendency of liquid within a compartment to remain level as the vessel is transversely inclined or heeled, provided the compartment has the following characteristics: (1) Is intact (2) Is partially flled (3) Allows the liquid to move unimpeded from side to side The free surface effect of loose water anywhere in the vessel impairs stability by raising the center of gravity in an apparent or virtual sense.NFPA 1405 pdf download.