Fire Hydrant

The Full Picture

A fire hydrant is a valved outlet on a pressurized water main. Most U.S. hydrants are the dry-barrel type, where the main valve sits below the frost line and the barrel stays empty until it is opened, which suits cold climates. Wet-barrel hydrants hold water in the barrel and are more common in warmer regions. A typical hydrant has two hose outlets and a larger pumper outlet. Public hydrants sit on a municipal main, while private hydrants sit on a site fire main owned by the property. The NFPA 24 standard governs private fire service mains and their appurtenances, and NFPA 291 covers hydrant flow testing and marking.

Hydrants usually appear on the civil site utility plan and fire service plan, not on the building plumbing plans. The plan shows each hydrant as a symbol with a tag, the lateral pipe running to the main, the valve, and notes pointing to a detail sheet. The detail shows depth of bury, the bedding, a thrust block or restraint, a drain gravel pocket, and sometimes protective bollards. The utility legend, the specification section for water distribution or fire service mains, and the fire marshal's review comments all affect the quantity. Fire code, often the International Fire Code as locally amended, sets where hydrants go and how far apart, so the count on the plan comes from that review rather than from the estimator.

The takeoff unit for the hydrant itself is each. A complete hydrant assembly commonly includes the hydrant, an auxiliary gate valve on the lateral, the tee or tap on the main, the lateral pipe in linear feet, restraints or thrust blocking, gravel at the drain, and the excavation and backfill. The pipe, valve, fittings and trench work are measured separately by size and priced alongside, which is where earthwork and utility trench quantities come in. Lateral size commonly runs 6 in, but the plan and spec state it. Paving or landscaping restoration around the hydrant is often carried with sitework rather than with the assembly.

Pricing mistakes tend to come from scope. The hydrant may be furnished and installed by the water utility, with the contractor paying only a fee or doing only the tie-in, or it may be fully in the site contractor's scope. A wet tap into a live main is a different line from a tee in a new main. Contractors also forget the lateral valve, the restraint hardware, or the pavement around it. Timing matters too: where underground mains are required, OSHA's construction fire-protection rule says they must be usable as soon as practicable, and that rule also notes that charged hose lines may be supplied by hydrants during demolition, so hydrants are often needed early in the schedule.