(a) Briefly explain why only considering convection is reasonable when deriving Response Time Index (RTI) of a sprinkler head. (6marks) (b) Briefly describe the procedure of designing the pipe layout of the sprinkler system in a room of OH2 fire hazard class. (7 marks) (c) Explain why water mist systems can be used for Class B fires. (6marks) (d) If using the plunge test for measuring the RTI of sprinkler head, the hot air temperature is (100+X)C and the air velocity is 1.5m/s, estimate the RTI of the sprinkler head of a red glass bulb if its activation time is measured as 80s. What will be the activation time if the air velocity is changed to 1.2m/s ? Note that the room temperature is assumed to be 20C. (In Q3,X is the 3rd digit of your student ID number. e.g. X=3 if your student ID is 12345678G. )