Drainage...Not Just Another Hole in the Ground
At first glance, drainage may not seem to be an important consideration in the design and installation of fire protection systems. However, if not considered early in the fire protection system design for a project, disregard for drainage requirements can have an impact on the overall building design coordination. Inadequately addressed drainage issues can even impact construction, especially in today's fast-track building atmosphere. Drainage serves a vital role during the final testing and acceptance phases for fire protection systems, as well as in the long-term maintenance and operation of these systems.
Drainage, as it relates to fire protection, should be considered on multiple levels. While drainage is usually associated with its usefulness in facilitating fire system maintenance and repair operations, it also proves useful in:
- Freeze protection
- Removal of wastewater from secondary fire system components (e.g. fire dept. and pump test connections, backflow preventers, pressure relief valves, etc.)
- System testing
- Alarm testing
- Monitoring/verification of system water supplies
- Containment and control of hazardous materials and associated fire spread
- Minimizing water damage and property loss in sensitive occupancies
National Fire Protection Association (NFPA) StandardsGenerally, adequate drainage is not an option, but a requirement, and it is specified by various NFPA standards related to the design, installation, and operation of fire suppression systems. Most, if not all, of these standards are referenced by the building and fire codes throughout the country. Some of the more prevalent NFPA standards include:
- NFPA 13--considered the "bible" for sprinkler system design;
- NFPA 20--covers the design and installation of fire pumps; and
- NFPA 11, 11A, and 16--requirements for a variety of foam and foam-water suppression systems.
NFPA Standards Compliance in Drainage ApplicationsAll of the above commonly used standards incorporate drainage as a component of the overall fire protection system design. The following examples will show how drainage plays an important role in the design and engineering of fire protection systems.
System Drain DownThe most common purpose of drainage is to remove water from a water-based fire suppression system, such as a fire sprinkler or a fire standpipe system. The NFPA standards indicate specific requirements for drain connection sizes based on size or capacity of the system piping. In order to ensure effective drainage the system piping must be designed in such a manner that all parts of the system can be drained. Gravity and pipe arrangements are big factors here.
Example: NFPA 13 typically requires a 2-inch "main drain" connection at the main system riser assembly. The main system riser assembly is located at the beginning of the system, typically where the fire water service enters a building, approximately 4 to 5 feet above the floor. The water in the system needs to be drained by gravity; therefore, the system piping must be installed so there are no trapped sections of pipe (i.e. up-and-down changes in pipe elevation). If this is done, most of the contents of the system piping can be drained back to the main drain connection.
Auxiliary DrainageMany times, it is impossible to completely eliminate trapped sections of piping in the design of a sprinkler system. Therefore, auxiliary drainage will be required. The size and arrangement of auxiliary drains depends upon the capacity of the trapped section or sections of pipe, and consequently, the larger the capacity of the trapped piping, the more elaborate the auxiliary drain connection. The main purpose of drainage here is to facilitate the repair, maintenance and modification of the fire suppression system piping while minimizing the potential that a contractor will disconnect a section of pipe and find the system contents have not been completely drained. Such a situation could lead to an uncontrollable release of the remaining water in the trapped piping. This water is generally not "clean" water. It will likely require clean up and could cause damage, especially to a newly renovated space. NFPA 13 requirements range from removing a pendent sprinkler in order to drain the trapped section of pipe, to providing a drain connection permanently piped and routed to the exterior of the building.
Freeze ProtectionDrainage is also a fundamental way of providing freeze protection for dry-pipe sprinkler and standpipe systems. Again, the NFPA standards require auxiliary drains strategically placed to collect and eliminate trapped water and condensation. Any trapped water or condensation left within suppression system piping could freeze, creating a plug in the system that could lead to a system failure. The result could be a pipe break from the expanding water or an ice-plug preventing water from moving through the system during a required system operation. Various NFPA standards also require that the system piping for dry-pipe systems be pitched in order to facilitate drainage to the provided drain points.
It should be noted that piping is permitted to be installed level (no pitch) for wet-pipe or preaction sprinkler systems that are located entirely within areas not subject to freezing.
Fire Department/Pump Test ConnectionsSimilar NFPA standards must also be implemented for fire department connections and fire pump test connections. Implementing these standards requires providing an automatic ball drip that allows trapped water to drain to an appropriate location. Typically, there is not a large amount of water in these cases; however, if trapped water did collect and freeze, it could prohibit the fire department from pumping into the system during a fire event.
Handling Backflow and DischargeAnother device commonly installed in fire suppression systems is a backflow preventer. This device is commonly required by local water companies to protect the public water system from a backflow and possible contamination via a connected sprinkler or standpipe system. In some cases, especially where chemical additives (such as antifreeze) are introduced to the system, a reduced-pressure principle backflow preventer is required. This type of backflow preventer incorporates a relief valve. A properly designed drain is provided to accommodate the maximum anticipated flow from this relief valve. Plumbing codes generally require an air gap be provided between the relief valve discharge outlet and the drain, and that the water discharge is readily visible or easily detectable.
Pressure Relief ValvesThere are various situations identified throughout the NFPA standards for which pressure relief valves are required in order to protect system components from exceeding their rated working pressure. Some of these are as follows:
- To protect system piping and components downstream of a fire pump, especially for variable speed driven pumps (i.e. diesel engine driven pumps);
- Where pump churn pressure (i.e. pressure at zero flow) plus maximum incoming water supply pressure exceed the rated working pressure of downstream components;
- To accept discharge from other fire pump miscellaneous components (i.e. circulation relief valves, packing box or drip rim drains, and cooling water discharge from diesel engine heat exchangers); and
- Relieving excess pressure build-up in gridded sprinkler systems due to temperature changes.
As part of relieving pressure, water is discharged. In the case of a fire pump, this can be a large quantity of water. The fire protection designer/engineer must coordinate with the plumbing or site/civil engineer to ensure that a drainage system of adequate capacity is provided to accept this discharge. Several options are:
- --Discharge outside to grade (see discussion in "System Testing" section regarding discharge)
--Discharge directly to a storm waste system
--Discharge to a sanitary waste system via an indirect waste connection
If none of these options is feasible, then a last option may be to discharge back to the suction side of the pump. This is typically not preferred by NFPA 20, but may be acceptable depending on the circumstances.
System Water Supply Testing/MonitoringDrainage also helps facilitate testing and verification of fire suppression system operation. The two-inch main drain located at the main sprinkler system riser assembly is commonly utilized to validate or monitor the available water supply at the incoming fire water service. The main drain is typically fully opened and allowed to remain open, flowing water until the pressure stabilizes. The static pressure is noted before the drain valve is opened and after the valve is closed. The residual pressure is noted while the valve is fully opened and water is flowing. This test serves as an accepted method of checking and monitoring the water pressure available from the water supply source.
If there are significant changes in the static and residual pressures recorded during a main drain test, this could indicate a reduced water supply, closed valve, or other fire water supply obstruction. This could prompt further testing and investigation. A fully open main drain valve can discharge between 100 and 200 gallons per minute. For this reason, the main drain is preferably piped to exterior grade. Consideration must be given to the discharge location so the above flow test can be performed for a sufficient amount of time to assure a proper test without causing water damage to the building or landscape. In general, the discharge needs to be directed away from the building in order to prevent water infiltration back into the building. If the discharge surface is soft-scape, such as plantings or lawn area, the provision of splash blocks or some other forms of hard-scape may be considered.
In certain instances, there may be local jurisdictional requirements or environmental regulations that prohibit sprinkler water discharge to grade, possibly because of chemical additives in the water (such as antifreeze added to non-freeze systems). As an alternative, discharge to the storm or sanitary sewer system may be a possibility but will need to be connected to such systems via an indirect waste connection in accordance with local plumbing codes. For these reasons, discuss local environmental and plumbing requirements with the local Authority(s) Having Jurisdiction (AHJ) prior to fire protection system design.
Waterflow Alarm TestingSprinkler systems also have requirements to incorporate alarm test connections, or what are commonly referred to as inspector's test connections. This test connection, though smaller in diameter, is similar to a drain connection. The inspector's test connection should preferably be in the upper story of a building or some other hydraulically remote point of the system. The connection should also preferably be piped from the end of the most remote branch line.
For dry-pipe systems, test connections must be located at the remote end of the system in order to test and verify that air can be removed from the system and water can reach the remote end of the system in the code-prescribed time limit.
There are instances where locating the test connection at the remote end of the system is not required, such as in:
- --Wet pipe or single-interlock pre-action sprinkler systems
--Combined sprinkler/standpipe systems
For these types of systems, the test connection is permitted to be positioned just downstream of the associated system flow switch located at the main system riser assembly or associated sprinkler zone. In the case of a combined sprinkler/standpipe system, as would be provided in a multi-story, a test/drain connection is typically located on each floor at the floor control valve assembly (FCVA), thereby creating separate sprinkler zones. The discharge from each FCVA test/drain connection is then tied into a common test/drain riser of appropriate size that parallels the standpipe riser in the stair and is typically discharged outside the building.
Drainage Discharge LocationGenerally, the discharge from test connections should be discharged to a point where it can be readily observed.
This is especially important for foam/water suppression systems. For these systems, a test connection is required to facilitate periodic checking of the performance of the foam/water proportioners. The test connection needs to be routed to an appropriate drain area, where the discharge of foam/water solution can be sampled as well as properly and safely disposed of.
In locations where it is not practical or possible to terminate the test connection to a visible location outside the building, the test connection is permitted to terminate into a plumbing drain inside the building capable of accepting full flow under system pressure. If discharging the test connection to a drain inside the building, the connection will typically need to be an indirect waste connection. In many instances, these connections are piped to a janitor's utility sink, a sump or possibly a floor drain. Keeping in mind, the receiving drain connection must be both large and deep enough to carry the flow and pressure of the test connection. Not doing so will result in water backing up beyond the intended receiver, which can damage surrounding areas. The other result may be that the test connections are never used or run full-open due to fears of causing damage.
Special Testing ConsiderationsDrains are also required to permit testing of specially required hose valves. For standpipe systems in high-rise buildings, pressure-regulating fire department hose valves may be needed to accommodate the high pressures experienced at the lower floors of the high-rise building. These higher pressures are the result of the inherent need to install high-pressure fire pumps in order to get water to the top floors of the building at the required minimum residual pressure of 100 pounds per square inch (psig), as required in NFPA 14. The higher pressure at the lower floors (possibly in excess of 175 psig) can subject firefighters to dangerous conditions in handling or operating fire hoses. If these regulating fire hose valves are installed, NFPA 14 requires a minimum 3-inch drain riser with appropriate connections to facilitate regular operational testing of these regulating hose valves.
Hazardous MaterialsDrainage should also be considered in retention or containment systems.
Drainage along with containment can be utilized as a method of controlling fire spread in areas used to store flammable or combustible liquids. In a flammable/combustible liquid storage/dispensing room, drainage and containment can incorporate several features to keep sprinkler discharge and burning flammable/combustible liquids from leaving the room, or to drain it away to a safe area such as a tank or remote impounding area outside the room or building. These features include:
- Sloped floors
- Recessed floor, suitable sized open-grate trenches, or pit
- Curbs, raised sills, thresholds, ramps of suitable height
- Special drains or scuppers to a safe location (i.e. floor drains, trench drains piped to a containment tank or a remote impounding area)
The drainage piping must have the capacity to accommodate the anticipated flow from the largest tank in the room or space, plus 30 minutes of the anticipated design discharge of the fire suppression system.
Obviously, these provisions only address fire protection concerns. As with all drainage solutions involving hazardous materials, environmental regulations and other requirements of the local AHJs must also be addressed in order to comply with any applicable requirements or restrictions. Adequate drainage/containment can keep any hazardous materials involved in a fire, or possibly the suppression agent itself (such as in the case of AFFF Foam), from reaching and contaminating environmental or human health-sensitive areas. The same approach can be used not only where flammable/combustible liquids are present, but where toxic, corrosive, or other hazardous materials are present, in order to control the spread of the materials.
Special Water Sensitive OccupanciesSimilarly, drainage can aid in removing sprinkler water discharge from an area sensitive to the effects of water, such as a computer room or other space with high value contents or equipment. For example, NFPA 75, which addresses computer/data-processing occupancies, requires provisions for drainage of discharge from various sources, including sprinkler operation discharge or hose stream flows from fire-fighting operations.
Another way drainage can be used involves elevator safety. ANSI/ASME A17.1 Safety Code for Elevators and Escalators requires that a permanent sump pump and pit be provided at the bottom of an elevator shaft. One reason for this requirement is to control discharge from sprinkler actuation that may occur in the shaft or elsewhere in the building in conjunction with hose stream flows. This discharge may make its way to the low point in the building, i.e. the elevator pit. For safety reasons, the code intends to remove any water that may make its way to the elevator pit to ensure safe and reliable elevator operation. The code does not allow floor drains in the elevator shaft. Therefore the discharge from the sump pump must be piped to a safe location above-grade, where it can be safely captured and disposed of in accordance with local plumbing code regulations and environmental regulations.
SummaryThese are just a few examples of drainage issues related to fire protection design and engineering. As noted, drainage plays an important part in everyday fire protection system designs and methods. These drainage issues need to be considered early in the fire protection design process so the necessary drainage components (such as sizing, routing, discharge points, access, capacity, etc.) can be properly coordinated with the rest of the building systems and incorporated into the overall building design.
Part 2 of this article can be found at www.pmengineer.com. In Part 2, possible methods of reducing or eliminating drainage requirements are considered. In addition, a Fire Protection System Drainage Design Checklist will be provided to help navigate through the various drainage concerns and requirements related to fire protection system design and engineering.