CombustionSection AIn approximately 250 words, discuss the different extinguishing methods of water, a powder and a carbon dioxide fire extinguisher. In fighting fire, there are different fire extinguishers that can be used to smother fire and stop its spread. The choice of extinguishing method depends on the type of fuel or the cause of fire. The main three different types of extinguishers contain water, powder, and carbon dioxide. The respective extinguishing method is only used where they starve and smothers fire ultimately killing it. In other classes of fires, water can assist in the spread and growth of the fire. Water extinguishers are used in fighting class A fires.
Class A fires are caused by burning carbonaceous materials such wood, papers, and textiles among others (The Fire and Safety Centre, 2014). Water cannot be used to fight fires caused by flammable fluids and electrical equipment. Powder extinguishers are used in fighting Class A fires as well. In addition, the powder is used in fighting Class B fires. Class B fires include those fires caused by flammable liquids, petroleum products, and spirits among others (The Fire and Safety Centre, 2014).
Also, the powder is used in Class E fires, which are usually caused by electrical equipment and may still contain electric current (The Fire and Safety Centre, 2014). The powder forms a solid layer on the burning substances depriving fire the necessary ingredient, oxygen, to grow. Carbon dioxide extinguishers are only used to fight two classes of fires; Class B and Class E. Carbon dioxide can be used alongside powder in fighting fires from flammable fluids and those caused by electrical equipments and may still contain electric current (The Fire and Safety Centre, 2014).
Carbon dioxide cuts the supply of oxygen to the burning surface by creating an inert layer on top of burning substances. Thus the fire dies out due insufficient oxygen supply. In approximately 250 words explain what is meant by, and the differences between, prescriptive and performance based design. In fire safety standards, there are codes and design specification that must be met when constructing different types of buildings. Prescriptive and performance based designs are used to incorporate specific building requirements and specifications to meet the safety standards required for the structure.
Prescriptive design is where specific requirements, span tables, pre-fined design options and rules are applied to develop a design that complies with the codes of required standards (Woodworks, 2014). The prescriptive design approach follows structural design standards that conform to the type of structure under construction. On the other hand, in the performance based design approach, there is not prescribed code of standards to follow when designing a building. However, the building under construction must meet some measurable and or predictable performance requirements (Woodworks, 2014).
In this approach, there are no prescribed means of achieving the performance-based requirement such as energy efficiency. One design approach cannot be used to replace the other. There are differences that exist between prescriptive and performance based designs. Prescriptive codes only allow for a minimum safety factor of 10%. On the other hand, performance based designs, safety factors are evaluated case by case basis, making several assumptions due to potential uncertainties involved (Building and Construction Authority, 2013). Owing to the unpredictable nature of fire, proper use of performance based design can used as an improvement to prescriptive based codes (Alaska Housing Finance Corporation, 2011).