NFPA 291

Question 1

NFPA 291. What codes are referenced.

Answer 1

Recommended Practice for Fire Flow Testing and Marking of Hydrants

Question 2

1.2 Purpose. Why are flow tests performed.

Answer 2

Fire flow tests are conducted on water distributions systems to determine the rate of flow available at various locations for fire-fighting purposes.

Question 3

1.3 Application. What results are produced.

Answer 3

A certain residual pressure in the mains is specified at which the rate of flow should be available. The residual pressure should be 1/2 static. No less than 20 psi residual.

Question 4

3.2.1 Authority Having Jurisdiction (AHJ). Define.

Answer 4

An organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials an installation or a procedure.

Question 5

3.2.2 Define Listed.

Answer 5

Equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with the evaluation of products or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluations of services, and whose listing states that either the equipment, material, or service meets appropriate designated standards or has been tested and found suitable for a specified purpose.

Question 6

3.3.1 Define Rated Capacity

Answer 6

The flow available from a hydrant at the designated residual pressure (rated pressure), either measured or calculated.

Question 7

3.3.2 Define Residual Pressure.

Answer 7

The pressure that exists in the distribution system, measured at the residual hydrant at the time the flow readings are taken at the flow hydrants.

Question 8

3.3.3 Define Static Pressure.

Answer 8

The pressure that exists at a given point under normal distribution system conditions measured at the residual hydrants with no hydrants flowing.

Question 9

4.1 Rating Pressure. What is the minimum rating pressures (Static/Residual).

Answer 9

For the purpose of uniform marking of fire hydrants, the ratings should be based on a residual pressure of 20 psi for all hydrants having a static pressure in excess of 40 psi. 4.1.2 Hydrants having a static pressure of less than 40 psi should be rated at one-half of the static pressure. 4.1.6 The use of residual pressures of less than 20 psi is not permitted by many state health departments.

Question 10

4.2 Procedure for testing.

Answer 10

4.2.1 Tests should be made during a period of ordinary demand. 4.3.1 Layout Determine location. 4.3.2 Consider potential interference. 4.3.3 Designate residual hydrant (for static and residual psi). 4.3.4 Located between the hydrant to be flowed and the large water supply mains. 4.3.5 Determine the number of flowing hydrants (must cause a drop in residual pressure of at least 25% or flow the total demand for necessary fire-fighting purposes).

Question 11

4.4.1 Equipment necessary for flow test.

Answer 11

(1) A single 200 psi bourdon pressure gauge with 1 psi graduations.
(2) A number of pitot tubes.
(3) Hydrant wrenches.
(4) 50 or 60 psi bourdon pressure gauges with 1 psi graduations.
(5) A hydrant cap tapped with a hole and a short 1/4” brass pipe for the T connection and the 200 psi gauge.

Question 12

4.5 Test Procedure.

Answer 12

4. 5.1 Attach 200 psi gauge to a 2-1/2 outlet of the residual hydrant.
5. 5.2 Open the cock on the gauge piping, open the hydrant completely.
6. 5.3 Exhaust the air and close cock.
7. 5.4 Read static pressure.
8. 5.6 Open flow hydrants one at a time.
9. 5.7 Flow for sufficient time to clear debris and foreign substances from stream(s).
10. 5.8 Read pitot pressures of all flow hydrants simultaneously while the residual pressure is read from residual hydrant.
11. 5.10 Slowly close each hydrant one at a time.

Question 13

4.7.1 Three General Types of Hydrant Outlets and Their Coefficients of Discharge.

Answer 13

1. Outlet smooth and rounded (coef. 0.90)
2. Outlet square and sharp (coef. 0.80)
3. Outlet square and projecting into barrel (coef. 0.70)
   This references the interior of the fire department connection outlet.

Question 14

4.7.3 Formula used to compute the discharge (Q) in gpm from these measurements.

Answer 14

Q = 29.84(cd^2)(sqrt p)
Where:
c=coefficient of discharge
d=diameter of the outlet in inches
p=pitot pressure (velocity head) in psi

Ex: 29.84(.9)(2.5^2)(sqrt20) = 750.6
Chart reflects c=1.0

Question 15

4.9 Determine discharge without a pitot.

Answer 15

4.9.1 A 50 or 60 psi gauge tapped into a hydrant cap can be used. 4.9.2 Place on the outlet and allow flow to take place the the other outlets at the same elevation. The readings obtained from a gauge so located and the readings obtained from a gauge on a pitot held in the stream, are approximately the same.

Question 16

4.10 Calculate results.

Answer 16

4.10.1 The discharge in gpm for each outlet flowed is obtained from Table 4.10.1(a) and Table 4.10.1(b) or by the use of Equation 4.7.3. 4.10.1.1 If more than one outlet is used, the discharges from all are added to obtain the total discharge. 4.10.1.2 Apply the formula to compute discharge at the specified residual pressure for any desired pressure drop.

Question 17

4.10.1.2 Formula for Discharge at Specified Residual Pressure.

Answer 17

Qr = Qf x (hr^0.54 / hf^0.54)
Where:
Qr = flow predicted at desired residual pressure
Qf = total flow measured during test
hr = pressure drop to desired residual pressure
hf = pressure drop measured during test

Question 18

4.13 Public hydrant testing and flushing periodic testing.

Answer 18

4. 13.1 Public fire hydrants should be flow tested every 5 years to verify capacity and marking of the hydrant.
5. 13.2 Public fire hydrants should be flushed at least annually to verify operation, address repairs, and verify reliability.

Question 19

5. Classification of Hydrants.

Answer 19

Class AA - Rated capacity of 1500 gpm or greater.
Class A - Rated capacity of 1000-1499 gpm.
Class B - Rated capacity of 500-999 gpm.
Class C - Rated capacity of less than 500 gpm.

Question 20

5.2 Marking of Public Hydrants

Answer 20

5. 2.1.1 All barrels are to be chrome yellow except in cases where another color has already been adopted.
6. 2.1.2 The tops and nozzle caps should be painted with the capacity indicating color scheme.

Question 21

5.2.1.2 Capacity Indicating Color

Answer 21

Class AA - Light blue
Class A - Green
Class B - Orange
Class C - Red

Question 22

5.2.1.4 Indication of Hydrant rated at less than 20psi.

Answer 22

5.2.1.4 Stencil the rated pressure in black on the hydrant top.

Question 23

5.2.1.9 Private hydrants on public streets

Answer 23

5.2.1.9 Private hydrants located on public streets should be painted red to distinguish them from public hydrants.

Question 24

5.2.2 Inoperative Hydrants markings

Answer 24

5. 2.2 Permanently Inoperative hydrants should be removed.

5. 2.3 Temporarily Inoperative Hydrants should be wrapped or indicated of their condition.

Question 25

5.2.5 Private Hydrant markings

Answer 25

5.2.5.1 Private hydrants within private enclosures is at the owner’s discretion.