SRS cheat sheet

Orifice flow from a sprinkler: Q = K × √P, with Q in gpm, P in psi, and K the sprinkler discharge coefficient.

Pressure and elevation conversion: 1 psi = 2.31 ft of water column; 1 ft of water column = 0.433 psi.

Hazen–Williams friction loss uses C = 120 for steel pipe and C = 150 for copper and plastic pipe in NFPA 13 calculations.

Reference design densities: light hazard 0.10 gpm/ft², ordinary group 1 = 0.15, ordinary group 2 = 0.20, extra hazard group 1 = 0.30 gpm/ft².

Glass-bulb temperature colors: 135°F orange, 155°F red, 175°F yellow, 200°F green, 286°F blue, 360°F purple, 440°F black.

Sprinkler rating is selected at least 30°F above the maximum expected ceiling temperature at the sprinkler location.

A wet system stores water at the valve; a dry system stores air and must deliver water to the inspector's test connection within 60 seconds of trip.

On the density/area curve, higher design densities are paired with smaller assumed operating areas for the same hazard class.

Hose stream allowance is added to the sprinkler demand, expressed in gpm for a stated duration (typically 30 to 120 minutes).

NFPA 13 (installation), NFPA 14 (standpipes), NFPA 20 (pumps), NFPA 25 (ITM), and NFPA 72 (alarm) are separate documents and can be enforced in different editions on the same project.

Model codes become legally enforceable only when adopted by a jurisdiction; the adopted edition and local amendments govern, not the newest published edition.

The authority having jurisdiction (AHJ) approves plans, grants modifications, and may impose inspection or test frequencies stricter than the standard minimum.

NFPA 25 monthly tasks include gauge readings, control valve position verification, and dry pipe or preaction air pressure checks.

NFPA 25 quarterly tasks include waterflow alarm device tests and valve supervisory (tamper) switch tests.

NFPA 25 annual tasks include the main drain test, fire pump flow test, dry pipe valve trip test, and alarm check valve test.

Backflow prevention assemblies protecting the potable supply are tested annually by certified testers under state and local cross-connection rules.

A code modification or accepted alternative must be documented in writing by the AHJ before the deviation is installed.

Standard spray sprinklers in ordinary hazard: maximum 15 ft spacing and 130 ft² per sprinkler; extra hazard: maximum 12 ft spacing and 100 ft² per sprinkler.

Standard pendent and upright deflectors sit 1 in to 12 in below the ceiling unless the individual listing states otherwise.

Three times rule: an obstruction is acceptable when the sprinkler is located within three times the obstruction's depth below the deflector plane.

Hydraulic calculation begins at the most remote sprinkler and adds elevation loss, hose stream allowance, device and backflow losses, then compares total demand to the supply curve.

Water supply flow test data used for design must be no more than 12 months old and adjusted for seasonal and daily demand variation.

Working plans require AHJ approval before installation and show occupancy classification, sprinkler layout, pipe sizes, hydraulic calculations, and material lists.

Fire pump curve checkpoints: shutoff (churn) pressure no more than 140% of rated pressure, and 150% of rated flow at no less than 65% of rated pressure.

Pipe schedule sizing is allowed only within limits on system area, occupancy, and pressure; all other systems require hydraulic calculation.

A hydraulic design placard at the riser states density, operating area, hose allowance, and duration so later changes can be evaluated.

Hydrostatic test: 200 psi for 2 hours; where maximum working pressure exceeds 150 psi, test at 50 psi above working pressure for the same duration.

Underground mains are flushed before connection to building piping at a flow producing roughly 10 ft/s velocity to clear debris.

An impairment program names an impairment coordinator, notifies the AHJ and insurer, tags the system, and establishes compensating measures until protection is restored.

Hot work requires a written permit, a fire watch during the work, and continued monitoring for at least 30 minutes after the work ends.

Lockout/tagout isolates energy at pumps, valves, and disconnects, with verification of zero energy before maintenance begins.

Dry pipe and preaction systems depend on correct priming water level, correct air pressure, and a working air source to keep trip time within limits.

Any field change that alters hydraulic demand - added heads, larger area, changed pipe - requires recalculation and AHJ approval against the design placard.

Antifreeze solution concentration must be measured and documented; certain high-concentration solutions are restricted because of flammability.

Weekly: fire pumps run at no flow (churn) for at least 10 minutes for electric drive and 30 minutes for diesel drive.

Monthly: gauge readings, valve position verification, and dry pipe or preaction system air pressure checks.

Quarterly: waterflow alarm tests through the inspector's test connection and valve supervisory switch tests.

Annual: main drain test, fire pump flow test, dry pipe valve trip test, and alarm check valve test.

Every 5 years: gauge replacement or calibration, internal inspection of dry and preaction piping, and hydrostatic test of dry standpipes at 200 psi for 2 hours.

Spare sprinkler stock: 6 spares for systems up to 300 sprinklers, 12 for 301 to 1000, and 24 above 1000, matching installed types.

Replacement sprinklers must match the original K-factor, temperature rating, orientation, and response type.

Inspection and test records are retained for at least 1 year and made available to the AHJ on request.

Risk control hierarchy: elimination, substitution, engineering controls, administrative controls, then personal protective equipment as the last layer.

Entry into tanks, vaults, and pits requires atmospheric testing, a permitted entry, an attendant, and rescue provisions.

Test water discharge must be controlled to prevent flooding, erosion, and uncontrolled runoff to storm or sanitary systems.

Backflow prevention assemblies protect the potable supply from cross-connection contamination and are tested annually by certified testers.

Freeze protection options are dry pipe, preaction, listed antifreeze solution, and added heat; wet pipe in an unheated space risks rupture and total loss of protection.

Seismic bracing, sway bracing, and flexible couplings limit pipe displacement and sprinkler damage in seismic zones.

Microbiologically influenced corrosion risk is highest in dry and preaction piping where trapped water and air coexist; internal checks occur at 5-year intervals.

Risk increases with impairment size and duration: longer and larger shutdowns require broader compensating measures such as fire watch and prohibition of hot work.

The hydraulic design placard at the riser records density, operating area, hose stream allowance, and duration; modifications may not exceed it without recalculation.

The contractor's material and test certificate documents flushing and hydrostatic test results, including pressures, durations, and signatures.

ITM reports record date, component, test method, result, and tester identity; the owner keeps a copy and retains records at least 1 year.

As-built drawings reflect installed conditions and approved changes and serve as the baseline for future plan review and modification.

Any AHJ variance, code modification, or accepted alternative is documented in writing and retained in the project file.

Water supply test documentation includes static pressure, residual pressure, pitot or flow data, the hydrant used, and the test date.

Professional practice requires reporting observed deficiencies accurately, never signing for work not performed, and disclosing conflicts to client and AHJ.