Sec. 14-9.4. Safety valve requirements

(a) Each boiler shall have at least one safety valve and if it has more than 500 square feet of bare tube water heating surface, or if an electric boiler has a power input more than 1,100 kw, it shall have two or more safety valves or safety relief valves. For a boiler with combined bare tube and extended water-heating surface exceeding 500 square feet, two or more safety valves or safety relief valves are required only if the design steam generating capacity of the boiler exceeds 4000 lb/hr. The method of computing the steam-generating capacity of the boiler is given as follows:

The maximum quantity of fuel C that can be burned per hour at the time of maximum forcing is determined by a test. The maximum number of heat units per hour, or CH, is then determined, using the values of H given in the Table below. The weight of steam generated per hour is found by the formula:

W =^{C × H}/₁₁₀₀ × 0.75

where

W = weight of steam generated/hr, lb

C = total weight or volume of fuel burned/hr at time of maximum forcing, lb or cu ft

H = heat of combustion of fuel, Btu/lb or Btu/cu ft (See Table below)

The sum ot the safety valve capacities marked on the valves shall be equal to or greater than W.

For the purpose of checking the safety valve capacity, the following values of heats of combustion of various fuels may be used:

	H = Btu/lb
Semibituminous coal	14,500
Anthracite	13,700
Screenings	12,500
Coke	13,500
Wood, hard or soft, kiln dried	7,700
Wood, hard or soft, air dried	6,200
Wood shavings	6,400
Peat, air dried, 25% moisture	7,500
Lignite	10,000
Kerosene	20,000
Petroleum, crude oil, Pennsylvania	20,700
Petroleum, crude oil, Texas	18,500
Municipal solid waste	7,800

	H = Btu/cu ft
Natural gas	960
Blast-furnace gas	100
Producer gas	150
Water gas, uncarbureted	290

(b) Organic fluid vaporizer generators require special consideration as given in the ASME Code.