Question

1-7. Identify the initiation, propagation, and termination steps for the following accident report. Suggest ways to prevent and contain the accident. b. An alkylation unit was being started up after shutdown because of electrical outage. When adequate circulation could not be maintained in a deisobutanizer heater circuit, it was decided to clean the strainer. Workers had depressurized the tank and removed all but three of the flange bolts when a pressure release blew a black material from the flange, followed by butane vapors. The vapors were carried to a furnace 100 ft away, where they ignited, flashing back to the flange. The ensuing fire exposed a fractionation tower and horizontal receiver drums. These drums exploded, rupturing pipelines, which added more fuel. The explosions and heat caused loss of insulation from the 8-ft X 122-ft fractionator tower, causing it to weaken and fall across two major pipelines, breaking piping – which added more fuel to the fire. Extinguishment, achieved basically by isolating the fuel source, took 2 ½ hours. The fault was traced to a 10-in valve that had been prevented from closing the last 3/4-inch by a fine powder of carbon and iron oxide. When the flange was opened, this powder blew out, allowing liquid butane to be released.

Answer 1

Ways To prevent & Contain the accident:

1. Use of proper SOP (Standard Operating Procedures) & checklists can avoid this type of accident.

2. Availability or presence of fire officer and a fire extinguisher near the working area is highly effective for elimination of fire during the initiation stage.

3. Complete purging of the area by nitrogen dilutes the presence of fuel gases that may not lead to a fire. So purging of the workplace is highly essential.

Containment:

1. The containment of fire is done by three methods

A. COOLING (Removal of heat)

B. Isolation(removal of fuel)

c. Blanketing(Removal of air )

Removal of heat is done by the use of water to terminate fire at source. Isolation of fuel pipe and eliminating fuel supply also terminate fire. This can be done by using the process logic shutdown. The blanketing is usually done by the use of fire extinguisher that eliminated contact of fire with air. This will also terminate fire.