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Hazard Survey

Hazard Survey. Dow Fire and Explosion Index is the most popular form of hazard survey. A formal systematized approach using a ranking form (similar to an income tax form). The final rating number provides a relative ranking of the hazards.

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Hazard Survey

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  1. Hazard Survey • Dow Fire and Explosion Index is the most popular form of hazard survey. • A formal systematized approach using a ranking form (similar to an income tax form). • The final rating number provides a relative ranking of the hazards. • The approach also contains a mechanism for estimating the dollar loss in the event of an accident.

  2. F&EI Form • Penalty column. Penalties for various unsafe situations are placed in this column. • The second column contains the penalty actually used. This allows for a reduction or increase in the penalty based on extenuating circumstances not covered in the form. In case of uncertainty, the value in the first column is used. • The final column is used for computation.

  3. Procedure • Conceptually divide the process into separate units. A process unit is a pump, a reactor or a storage tank, etc. Select the units that experience shows to have the highest likelihood of hazard. • Determine the material factor (MF). Procedures are available for mixtures and materials not listed in Table.

  4. Procedure • Determine the general process hazards. Penalties are applied for - Exothermic reactions that might self-heat. - Endothermic reactions that could react due to an external heat source such as a fire. - Material handling and transfer, including pumping and connection of transfer lines. - Enclosed process units preventing dispersion of escaped vapors. - Limited access for emergency equipment. - Poor drainage of flammable materials away from the process unit.

  5. Procedure 4. Penalties for special process hazards - Toxic materials. - Less than atmospheric pressure operation with a risk of outside air entering. - Operation in or near the flammable limits. - Dust explosion risk. - Higher than atmospheric pressure. - Low temperature operation with potential embrittlement of carbon steel vessels.

  6. Procedure 4. Penalties for special process hazards - Quantity of flammable material. - Corrosion and erosion of process unit structure. - Leakage around joints and packings. - Use of fired heaters, providing a ready ignition source. - Hot oil heat exchange systems where the hot oil is above its ignition temperature. - Large rotating equipment, including pumps and compressors.

  7. Computation of F&EI • The general process hazard factor: F1 • The special process hazard factor: F2 • The unit hazard factor: F3=F1×F2 • F&EI=MF×F3

  8. Degree of Hazard

  9. Consequence Analysis • MPPD: the maximum probable property damage. • MPDO: the maximum probable days outage. • Worksheet in Figure 10-4

  10. Risk Analysis Summary • F&EI (A-1) + correlation → • damage radius (A-2) → • Dollar value of the equipment with damage radius (A-3) • Correlation → Damage factor (B) • A-3 × B = base MPPD (C) • Credit factor: D = C1 × C2 × C3 • C × D = actual MPPD (E) → • Correlation + E → MPDO (F)

  11. Example A gasoline filling station contains a 10000 gallon tank with 4 gas pumps. The tank is stored underground and vented to the air. Proper vents with flame arrestors are provided. The tank is made of steel. Some deterioration by corrosion. The station has both fixed CO2 fire extinguisher and portable equipment. A remote shutdown control is installed in the station house.

  12. Solution • MF=16 (Table 10-1) • General process hazards: Item C Penalty = 0.5. Thus, F1=1.0+0.5=1.5 • Special process hazards: Item A penalty = 0.2, Item C1 penalty = 0.5, Item C3 penalty = 0.8, Item G:

  13. Solution • Figure 4 + Correlation B →G2 penalty = 0.4 • Item H penalty = 0.1 • F2 = 3.0 • F3 = 1.5 × 3.0 = 4.5 • F&EI = 4.5 × 16 = 72.0 • Moderate!

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