Drainage Systems for Flammable Liquids

March 1991Revised May 2000

Page 1 of 17

DRAINAGE SYSTEMS FOR FLAMMABLE LIQUIDS

Table of ContentsPage

1.0 SCOPE ................................................................................................................................................... 21.1 Changes .......................................................................................................................................... 2

2.0 LOSS PREVENTION RECOMMENDATIONS ....................................................................................... 22.1 Introduction ...................................................................................................................................... 22.2 Construction and Location ............................................................................................................... 3

2.2.1 General Considerations for Drainage .................................................................................... 32.2.2 General Considerations for Containment .............................................................................. 42.2.3 Design of Drainage and Containment ................................................................................... 42.2.4 Alternatives to Drainage ...................................................................................................... 11

2.3 Operation and Maintenance .......................................................................................................... 133.0 SUPPORT FOR RECOMMENDATIONS ............................................................................................. 14

3.1 Comments on Recommendations ................................................................................................. 143.2 Loss History ................................................................................................................................... 153.3 Illustrative Losses .......................................................................................................................... 15

3.3.1 Paint Distribution Center Destroyed .................................................................................... 153.3.2 Farm Supply Warehouse ..................................................................................................... 15

4.0 REFERENCES ..................................................................................................................................... 164.1 FM Global ...................................................................................................................................... 164.2 NFPA Standards ............................................................................................................................ 16

APPENDIX A GLOSSARY OF TERMS ..................................................................................................... 16APPENDIX B DOCUMENT REVISION HISTORY ..................................................................................... 16APPENDIX C BIBLIOGRAPHY ................................................................................................................. 17APPENDIX D CONFLICTS WITH NFPA ................................................................................................... 17

List of FiguresFig. 1. Decision tree for drainage/containment. ............................................................................................. 2Fig. 2. Capacity of floor drains. ...................................................................................................................... 7Fig. 3. Nomograph for computing size of circular drain, flowing full. .......................................................... 10Fig. 4. Typical drainage system for a multi-unit outdoor facility. ................................................................. 12Fig. 5. Sealed inlet catch basin. .................................................................................................................. 12Fig. 6. Dry box catch basin. ......................................................................................................................... 13

List of TablesTable 1. Flow in Trenches ............................................................................................................................. 8Table 2. Flow through Pipe ............................................................................................................................ 9

FM GlobalProperty Loss Prevention Data Sheets 7-83

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1.0 SCOPE

This loss prevention data sheet provides guidelines for the design of drainage systems to minimize firedamage in areas using or storing flammable liquids. The design of system components not directly relatedto fire protection, such as flammable liquid/water separators and environmental protection requirements arenot covered, except by reference. Due to the many tiers of regulations (federal, state or provincial and local),the variance in regulations from country to country, and the very extensive nature of regulations within anygiven jurisdiction, this data sheet does not address environmental protection regulations, and is not intendedto ensure that drainage systems are in compliance with those protection regulations. However, all recom-mendations are made with an awareness that applicable regulations may limit the design of a drainagesystem.

1.1 Changes

January 2000. This revision of the document has been reorganized to provide a consistent format.

2.0 LOSS PREVENTION RECOMMENDATIONS

2.1 Introduction

Where automatic sprinklers or other water suppression systems are provided as the primary fixed protection,provide containment and emergency drainage as required by other data sheets for flammable liquid stor-age or use the guidelines provided below.

2.1.1 Provide containment as described in Recommendation 2.2.2 as minimum protection, except as notedbelow in Recommendation No. 2.1.2, where the only flammable liquids used or stored have a flash pointabove 200°F (93°C) or are water soluble, heavier than water (specific gravity greater than 1), or highly viscous.(See Fig. 1).

a) Water from sprinklers will float on liquids that are insoluble and heavier than water to extinguish a fireby smothering action.

b) Fires in water miscible liquids such as methyl alcohol can be extinguished by dilution with sprinklerwater. Note: To dilute one volume of alcohol to the point where it is nonflammable requires the additionof four volumes of water. Other liquids may require more or less water to make them nonflammable.

c) High-viscosity liquids (viscosity greater than 10,000 centipoise) need containment only. Generally, high-viscosity liquids do not flow freely and will obstruct drains.

Fig. 1. Decision tree for drainage/containment.

7-83 Drainage Systems for Flammable LiquidsPage 2 FM Global Property Loss Prevention Data Sheets

©2003 Factory Mutual Insurance Company. All rights reserved.

2.1.2 Where containment alone (without emergency drainage) would be acceptable based on the conditionsenumerated in Recommendation 2.1.1 and illustrated in Figure 1, adequate emergency drainage shouldnevertheless also be provided if there are one or more of the unfavorable conditions listed below:

a) High-value exposed areas or equipment where prompt removal of spilled or burning flammable liquidsis needed to minimize damage or production interruption. For example, a process with extensivecomputerized analytical instrumentation.

b) A high frequency of occurrence due to design or layout where routine spills or fires are inherent hazards.For example, some coating operations have almost monthly fires.

c) Liquid damage potential to nearby equipment. For example, a paint dipping operation where waterand spilled solvent could flow into an adjacent assembly area.

d) Weak fire protection water supplies. Although sprinklers will eventually extinguish fires in high flashpoint or water soluble liquids, extinguishment may not be achieved prior to operating sprinklers over agreater area than that expected if the burning liquids were promptly drained from the area.

e) Where local conditions do not allow construction of adequate containment for the anticipated spill.For example, confining the contents of a large tank inside a small room could require a curb several feethigh at the doorway.

2.1.3 Where a foam water sprinkler system is provided instead of a water suppression system:

a) Provide containment as described in Recommendation 2.2.2 where installation of drainage isimpractical and there are no unfavorable conditions.

b) Install drainage and containment where the unfavorable conditions listed in Recommendation 2.1.2above are present.

2.2 Construction and Location

2.2.1 General Considerations for Drainage

2.2.1.1 Design emergency drainage systems to remove the total anticipated water flow as detailed in Section2.2.3.2.

2.2.1.2 Arrange piping from floor and trench drains as follows:

a) Size the piping from floor and trench drains to adequately handle the flow collected as detailed inSection 2.2.3.2.

b) Provide traps where possible so that discharged flammable liquids will not continue to burn at thecollection point.

c) Provide fittings and ports to facilitate inspection and cleaning.

d) Design and locate liquid separator tanks so that liquid does not back up in piping between the hazardand separator.

2.2.1.3 Arrange emergency drainage systems to discharge to a storage location for recovery of flammableliquids and waste water treatment. At medium-to-large facilities, installation of a separator tank to removeflammable liquids, where permitted by local authorities, or impounding basins to collect flammable liquids maybe practical.

2.2.1.4 Size emergency drainage system impounding basins or collection facilities to hold the total drainagesystem discharge for the duration of the sprinkler operation, plus other liquids normally stored in the collectionfacility.

2.2.1.5 Provide distance, diking and drainage from open flammable liquid separator or collection basins toimportant structures or exposed property in accordance with Data Sheet 7-88, Flammable Liquid StorageTanks, for storage tanks of equivalent size and flashpoint. If closer spacing is necessary, provide automaticwater spray or equivalent protection on important exposed property and manual protection (i.e., foamcapability) for the basin.

Drainage Systems for Flammable Liquids 7-83FM Global Property Loss Prevention Data Sheets Page 3


2.2.1.6 Drainage system piping should preferably not have any valves. However, if one or more valves arenecessary, they should be located so as to be accessible in the event of a fire and should be normally keptin the fully open position.

2.2.1.7 Drainage system piping should preferably be of steel, concrete, or tile.

Plastic piping can be used if it can be ensured that the piping will not be exposed by flames or other intenseheat source. For example, if plastic pipe runs unburied through an open area below the drained area, thenit should be ensured that the floor of the drained area is liquid-tight to prevent any released flammable liq-uid from infiltrating the area below. If plastic pipe is to be used unburied, then a reinforced thermoset plas-tic pipe is preferred over one made of a thermoplastic material.

2.2.1.8 Drainage may be provided by wall scuppers, floor drains, and/or trench drains as described in Sec-tions 2.2.3.3, 2.2.3.4, and 2.2.3.5 below. Use of trench drains is preferred for the most effective drainage.Floor drains are the second preferred approach due to the limitations on the use of wall scuppers.

2.2.2 General Considerations for Containment

2.2.2.1 Confine flammable liquids with curbs, liquid tight walls sealed to the floor, depressed floors in theflammable liquid area, or grated drained trenches around the entire perimeter of areas which cannot be walledoff.

2.2.2.2 Use watertight floors in flammable liquid areas to prevent leakage to unsafe areas. (See Data Sheet1-24, Protection Against Liquid Damage, for design information.)

2.2.2.3 Use blank liquid-tight walls sealed to the floor and make all openings into the flammable liquid roomfrom the outdoors where possible to provide the optimum containment. If interior openings must be madein these walls, they should be above the level of minimum curb height specified in Section 2.2.3.1.

2.2.2.4 Construct a ramp or curb, as specified in Section 2.2.3.1, across all interior doorways from the flam-mable liquid room to prevent flow into adjacent areas. If ramps or curbs cannot be used, construct a gratedtrench at each doorway. Provide drains in the trenches as described in Recommendation 2.2.2.8.

2.2.2.5 Arrange trenches at doorways to prevent liquid flow between the trench and the wall to ensure liquidscannot flow through the doorway. Contractors frequently wish to install doorway trenches several inchesout from the wall to avoid footings beneath the wall. This allows liquid to flow around the ends of the trenchand is unacceptable.

2.2.2.6 Extend doorway trenches a minimum of 3 in. (76 mm) beyond both sides of the door jamb.

2.2.2.7 Where both drainage and containment are needed, provide a sufficient number of drains to main-tain the water level from automatic sprinklers and hose streams in the room at least 2 in. (51 mm) below thetop of ramps or curbs.

2.2.2.8 Where only containment is needed as noted in Section 2.1 and perimeter and/or doorway trenchesare used, install drains in the trenches. Drains should be sized to collectively handle the full sprinkler systemflow and hose demand of the contained area. Any lesser drainage capacity would allow liquids to spill past thetrench, thus compromising its intended use as a containment feature. The use of trenches in applicationswhere only containment is needed will bring about the added cost of a full drainage system and safe storagelocation. These costs would not be incurred with the use of other containment alternatives. Four in. (102 mm)high curbs or ramps are an alternative to perimeter trenches, except curbs should be high enough to containthe contents of tanks likely to release suddenly, such as oil filled transformers, plus 2 in. (51 mm) freeboard.

2.2.2.9 Pitch floors toward drains with a slope of at least 1⁄8 in. per ft (10 mm/m). A slope of 1/10 in. per ft(8.3 mm/m) is tolerable in existing storage areas previously constructed in accordance with Data Sheet 7-29,Flammable Liquid Storage in Portable Containers.

2.2.3 Design of Drainage and Containment

2.2.3.1 Curb design

Where curbing is provided in conjunction with adequate drainage, the curb should be a minimum of 4 in.(102 mm) high. Higher curbing may be provided if additional head is desired above the drains so as to increasedrainage flow rate.



Where curbing is provided without drainage, design curbs or ramps to confine flammable liquid spills inaccordance with the following:

2.2.3.1.1 Determine the largest expected flammable liquid spill as follows:

a) In areas used for storage in drums or smaller container that do not contain larger vessels, tote bins,or tanks assume the maximum spill is 220 gal (830 dm3). This assumes that four 55 gal (210 dm3) drumson a single pallet load could be speared by lift truck forks or damaged if a pallet load is dropped. If drumsare not handled on pallets and hand trucks or clamp type lift trucks are used, the amount of spill can bereduced, but no lower than the amount of the largest container (i.e., 55 gal [210 dm3] if drums are present).

b) In areas used for storage of flammable liquids in tanks, tote bins or other bulk containers assume themaximum spill is the contents of the largest container.

2.2.3.1.2 Determine the minimum curb height needed to confine the content of the largest flammable liquidspill using the following formula:

Q×12 +2 = H (1)A×7.48

Where, Q = maximum spill (gals)A = area of room or containment area (ft2)H = calculated curb height (in.)2 = 2 in. allowance for freeboard

In metric units,

Q +.05 = H1000A

Where, Q = maximum spill (dm3)A = area of room or containment area (m2)H = calculated curb height (m).05 = .05 m allowance for freeboard

Subtract the floor areas occupied by large tanks other than the chosen spill vessel and equipment from thearea of the room or containment area (A). This is especially important in rooms with many large tanks.

If H is greater than 4 in. (102 mm), use the calculated curb height as the minimum curb height. If H is equalto or less than 4 in. (102 mm), construct 4 in. (102 mm) high curbs.

2.2.3.2 Drainage Flow Requirement

2.2.3.2.1 Design emergency drainage systems to handle the total combined water flow from all of thefollowing:

a) The water expected to be discharged from building and in-rack sprinklers, water spray nozzles, andother fixed fire protection systems. Where open head deluge systems are used, anticipate operation of allsystems within a 100 ft (31 m) radius circle.

b) The water demand for hose streams.

c) Any production or domestic water normally discharged into the drainage system.

d) Surface water at outdoor location (see Data Sheet 9-2, Surface Water, for rainfall intensity).

2.2.3.2.2 The volume of the anticipated flammable liquid spill need not be incorporated into the calculationof drainage flow requirements where the volume of the spill is negligible as compared to the total water flow.For example, the anticipated spill in a drum storage warehouse would be four drums or 220 gal (835 dm3) totalvs. a water flow of 1,750 gpm (6625 dm3/min).

2.2.3.2.3 Determine the theoretical sprinkler water flow from the sprinkler system hydraulic calculations ormultiply the required sprinkler density by the sprinkler operating area. Adjust this demand as noted below toensure the drainage system is not undersized where the available fire protection water supply exceeds theminimum required water supply.



2.2.3.2.4 Determine the actual sprinkler water flow by plotting curves of the sprinkler system water demandand water supply after allowing for hose streams on semiexponential (N1.85) graph paper. The intersectionof the water demand and supply curves indicates the realistic water flow requiring drainage during a fire. (SeeData Sheet 3-0, Hydraulics of Fire Protection Systems, for examples of water flow calculation method.)

2.2.3.3 Wall Scuppers

Wall scuppers may provide adequate drainage where local conditions, including federal, state and local regu-lations, allow their installation in accordance with the recommendation listed below. However, the use of wallscuppers will be impractical at some locations. If the criteria listed in the recommendations cannot be met,use another more suitable form of drainage.

2.2.3.3.1 Direct discharge from wall scuppers away from important facilities and neighboring properties tominimize the fire exposure. Burning flammable liquids can be carried through the scuppers.

2.2.3.3.2 Direct the discharge from wall scuppers onto liquid-tight surfaces arranged to drain to a safecollection point.

2.2.3.3.3 Limit the use of wall scuppers to narrow rooms. Wall scuppers are relatively ineffective when theliquid to be drained must travel more than 75 ft (23 m) to the scupper.

2.2.3.3.4 Determine the approximate number of 4 in.×4 in. (102 mm×102 mm) wall scuppers needed by divid-ing the maximum expected sprinkler and hose stream water flow rate by 75 gpm (0.28 m3/min) which isthe scupper discharge capacity. Multiply this number of scuppers by 1.25 to account for blockage and thenround up to the nearest whole number. This is the minimum number of scuppers needed.

2.2.3.3.5 The following equation may be used to determine the approximate capacity of wall scuppers havingother dimensions where the liquid depth inside the room can be expected to fill the full height of the scupper.

Q = 1,500 (W - 0.2H)H1.5 (English units)Q = 1.1×105(W - 0.2H)H1.5 (Metric units)

Where, Q = flow in gpm (dm3/min)H = height of scupper in feet (meters)W = Width of scupper in feet (meters)

2.2.3.3.6 Consider the possibility of using a modified wall scupper arrangement where local regulations pro-hibit the use of wall scuppers and other drainage arrangements are impractical. The intent of such regula-tions may be to prevent discharge of liquids during routine liquid spills where there is no fire. For example, onelocation installed wall scuppers raised sufficiently above the floor to contain 10% of the total liquid volumeof the room or the volume of the largest container, whichever was greater, during a spill.

2.2.3.3.7 Where modified wall scuppers are proposed, consider the following limitations:

a) Raised scuppers could allow the entire room area to be covered with burning flammable liquid beforefuel starts to flow from the scuppers. Where this results in an unacceptable increase in the anticipatedfire damage consider use of a more suitable form of drainage or reducing the room size.

b) The longer retention of burning liquids caused by raised scuppers could open all automatic sprin-klers in the room. Use the entire room area as the sprinkler operating area in designing sprinkler sys-tems and water supplies. This may not be a concern for smaller rooms as the sprinkler operating area forflammable liquid areas is usually 5,000 ft2 (465 m2) or the entire area of the room, whichever is smaller.

c) Provide higher curbs or ramps at interior doorways as needed where raised scuppers are used toensure that the minimum vertical distance from the top of the curb or ramp to the maximum expected liquidlevel with fire protection systems operating is at least 2 in. (51 mm).

2.2.3.4 Floor Drains

Design or evaluate the installation of floor drains in accordance with the following:

2.2.3.4.1 Standard floor drains consist of a sunken box with a flush grating. Since these drains may be eas-ily blocked by debris, the floor gratings generally have a free area twice that of the outlet pipe. The nomi-nal size of a standard floor drain is the size of the outlet pipe, not the diameter of the inlet grate. The mostcommon floor drains have 4 or 6 in. (102 or 152 mm) outlet pipe connections.

7-83 Drainage Systems for Flammable LiquidsPage 6 FM Global Operating Standards


2.2.3.4.2 In order to overcome the restriction of the grating, liquid must build up over the drain to reach designcapacity. If standard floor drains are used, provide for sufficient head to allow the drains to reach the designcapacity by pitching the floor toward drains or providing curbs. Locating the drain in a trench will also ensuresufficient head.

2.2.3.4.3 Use Figure 2 to determine the theoretical number of drains needed when the expected head willbe 3 in. (76 mm) or less. Figure 2 shows the water flow capacity of 4 in. (102 mm) and 6 in. (152 mm) drainswith various heads.

Caution: Item 2.2.2.8 above requires a 2 in. (51 mm) freeboard from the maximum expected liquid level tothe top of doorway curbs. For example, where 4 in. (102 mm) high curbs are used, the head used to designdrains will be only 2 in. (51 mm) after allowing the required 2 in. (51 mm) freeboard.

2.2.3.4.4 For applications where 5 in. (127 mm) or higher curbs, dikes, or walls will assure a 3 in. (76 mm)head, use the maximum practical flow per drain to determine the theoretical number of drains needed. Asshown in Figure 2, the maximum practical flow from a 4 in. (101 mm) drain is 175 gpm (660 dm3/min) with3 in. (76 mm) head and the maximum practical flow from a 6 in. (152 mm) drain is 410 gpm (1550 dm3/min).

2.2.3.4.5 Increase the theoretical number of drains needed by 25% to 50% depending upon local condi-tions to allow for clogging. In areas where the total number of drains is small, such as four, increase the num-ber of drains by 50% for a total of six drains. The probability of all drains becoming clogged simultaneouslyis more remote for larger areas. Thus, use a smaller allowance (25%) for clogging in large areas.

Fig. 2. Capacity of floor drains.



For example, a 40 ft×100 ft (12.2 m×30.5 m) flammable liquid room has 4.75 in. (121 mm) high doorwaycurbs. Sprinkler calculations indicate that the sprinkler system will deliver an average density of 0.30 gpmper ft2 (12 mm/min) over the 4,000 ft2 (372 m2) room, producing a sprinkler flow of 1,200 gpm (4540 dm3/min). This flow, plus 500 gpm (1895 dm3/min) for hose streams, requires drainage for a total flow of 1,700 gpm(6435 dm3/min) (see Section 2.2.1).

A 2 in. (51 mm) freeboard at the 4.75 in. (121 mm) curbs allows a 2.75 in. (70 mm) head over the drains. Fig-ure 2 shows that the flow from a single 6 in. (152 mm) drain would be 410 gpm (1550 dm3/min). Divide thetotal flow (1,700 gpm [6435 dm3]) by 410 gpm (1550 dm3/min) to find that the theoretical number of 6 in.(152 mm) drains needed is 4.15. Round this number up to the next whole number or five. Increase the theo-retical number of drains by 25 to 50% to allow for clogging. Install seven drains.

2.2.3.5 Trench Drains

2.2.3.5.1 Use trench drains rather than standard floor drains whenever possible due to several advantagesas follows:

a) Trench drains maximize the flow through the drain system by ensuring an adequate head above drainoutlets.

b) Trench drains can also be used to confine flammable liquid spill fires where the liquid should not flowbeyond the drain grating or to subdivide process areas, tanks, etc.

Trenches installed between rows or tanks, drum storage racks, etc. can catch runoff from a spill withoutexposing adjacent areas. (See Figure 4 for examples.)

2.2.3.5.2 To determine the trench grating length needed divide the total flow required by 60 (745 for metricuses) and round up to the nearest whole number. A trench drain receives a flow of 60 gal/min/linear ft (745dm3/min/m) of trench with no buildup of liquid over the trench.

For example, a sprinkler density of 0.60 gpm per ft2 (24 mm/min) over a 40 ft×50 ft (2,000 ft2) (12 m×15 m[180 m2]) drum storage room results in a sprinkler flow of 1,200 gpm (4540 dm3/min), plus a 500 gpm (1895dm3/min) hose stream flow. The required drainage is 1,700 gpm (6435 dm3/min). When the required drain-age is divided by 60 and rounded up, 29 ft (8.6 m) of trench is needed.

2.2.3.5.3 Use Table 1 to ensure a properly sized trench and appropriate pitch to handle the expected flow.The size of the trench and its pitch controls the capacity of the drain.

For example, 1,700 gpm (6435 dm3/min) capacity is needed for the drum storage room in the above example.Table 1 shows that a 1 ft×8 in. (0.3×0.2 m) trench with a slope of 1⁄2 in. per ft (0.04:1) could handle 1,950 gpm(6800 dm3/min) and would be adequate. Where local conditions would not allow such a steep pitch, a 1 ft× 1 ft (0.3 m×0.3 m) trench with a pitch of 1⁄8 in. per ft (0.01:1) or a 2 ft×8 in. (0.6 m×0.2 m) trench with a slopeof 1/10 in. per ft (0.008:1) would also be adequate.

Table 1. Flow in Trenches

Trench Capacity (gal/min)Trench

Dimensions (W×D)Slope (in./ft)

1⁄10 1⁄8 1⁄4 1⁄21 ft×8 in. 850 950 1350 1950

1×1 ft 1550 1700 2400 34002 ft×8 in. 2100 2400 3400 4800

2×1 ft 4000 4500 6300 90002×2 ft 10,300 11,500 16,400 23,200

Trench Capacity (m3/min)Trench

Dimensions (W×D)Slope (m/m)

0.008:1 0.01:1 0.02:1 0.04:10.3×0.2 m 3.0 3.3 4.6 6.80.3×0.3 m 5.3 6.0 8.5 12.10.6×0.2 m 7.5 8.4 12.2 17.00.6×0.3 m 14.0 15.5 22.0 31.50.6×0.6 m 36.5 41.0 58.0 82.0



2.2.3.5.4 Use Table 2 to size the outlet pipe from the trench and/or determine the size and number of drainoutlets needed in a trench where the trench does not carry the liquid directly to the point of disposal. (Mostindoor trenches will connect to the drainage system via drain outlets and pipes, while some outdoor trenchinstallations may carry the liquid directly to the point of disposal.)

2.2.3.5.5 Select the diameter of the drain pipes to be installed and a practical pitch for the installation. Dividethe total required drainage by the flow shown in Table 2 for that diameter pipe and pitch. Round up to the near-est whole number to determine the minimum number of drains needed from the trench. To allow for block-age, multiply the minimum number of drains needed by 1.25 and 1.5. Select a whole number of outlets fromwithin this range.

For example, 1,700 gpm (6.4 m3/min) capacity is needed for the drum storage room in the above example.Table 2 indicates that an 8 in. (203 mm) outlet pipe with a pitch of 1 in. per 4 ft (21 mm/m) can handle 680 gpm(2.57 m3/min). Dividing 1,700 gpm by 680 gpm yields 2.5. This is rounded up to determine that the mini-mum number of outlets is 3. To allow for blockage, 3×1.25 = 3.75 and 3×1.5 = 4.5. The whole number ofdrains in this range is 4, which is the number of drains required.

2.2.3.5.6 As a final step, ensure that the free area of the trench grate is at least three times the area of theoutlet pipe(s) because the liquid head over the grate is less than the liquid head over the outlet pipe.

Calculate the area of each outlet pipe (for circular pipes area = π×r2, where π = 3.142 and r is the radiusof the pipe). Where there is more than one outlet pipe, add the areas of the individual outlets to determinethe total outlet pipe area. Calculate the free area of the grating (length×width) and compare this to the areaof the outlet pipe(s). If the grating area is less than three times the outlet pipe area, redesign the trench to pro-vide a larger grating area.

2.2.3.6 Drainage System Discharge Piping

2.2.3.6.1 Ensure an adequate method of carrying the liquid that has entered the drain(s) to the point ofdisposal. In the case of standard floor drains and some trench drains this is accomplished by piping.

2.2.3.6.2 Determine the pipe sizes needed for drainage by assuming that the pipes will flow full and all the ver-tical head between floor level and the point of discharge to free atmosphere can be used to overcome pipefriction, neglecting velocity head losses. The carrying capacity of drain piping is a function of pipe diam-eter and pipe pitch.

Table 2 shows the approximate capacities of common concrete or tile drain pipes for low flows. Once therequired flow is known, an appropriate pipe size and pitch can be selected directly from that table.

Table 2. Flow through Pipe

NominalPipe

Diameter

Pitch in./ft (mm/m)1⁄8 (10)

gpm (m3/min)

1⁄4 (21)gpm (m3/min)

1⁄2 (41)gpm (m3/min)

Verticalgpm (m3/min)

2 in.(50 mm)

— — — 30 (0.11)

3 in.(75 mm)

35 (0.13) 50 (0.19) 70 (0.26) 90 (0.34)

4 in.(100 mm)

80 (0.30) 110 (0.42) 160 (0.60) 190 (0.72)

5 in.(125 mm)

140 (0.53) 200 (0.75) 280 (1.06) 360 (1.36)

6 in.(150 mm)

225 (0.85) 315 (1.20) 445 (1.68) 560 (2.12)

8 in.(200 mm)

480 (1.82) 680 (2.57) 960 (3.63) 1200 (4.54)

For larger flows and/or pipe sizes, the nomograph in Figure 3 may be used. Place a straight edge acrossthe required drain flow and the pipe slope, to read the required pipe diameter for concrete or tile pipe directlyfrom the scale.

For example, a discharge of 2,000 gpm (30.3 m3/min) from a large outdoor chemical process area wouldrequire a 15 in. (380 mm) diameter concrete drain with a slope of 0.6% (pitch of 1 in./15 ft [.006:1]).

Drainage Systems for Flammable Liquids 7-83FM Global Operating Standards Page 9


Fig. 3. Nomograph for computing size of circular drain, flowing full.



Note: Table 2 and Figure 3 are for commonly used concrete or tile drain pipes and are intended for approxi-mate evaluations of drainage adequacy and for preliminary drainage layouts. Use of other pipe materials,unusually long pipes, changes in flow direction through fittings, etc. affect drainage system capacity. Finalworking plans for drainage installations should be prepared by experienced personnel using accepted engi-neering practices.

2.2.3.6.3 Use Table 1 to estimate the minimum trench size and slope when the required drainage flow isknown and trenches are used to direct drainage system discharge from the protected area to a safe dis-posal point as noted in Section 2.2.3.5. Use of trenches may be most appropriate for outdoor areas whereburning liquids would not expose important facilities.

2.2.3.6.4 Arrange drainage systems protecting multiple hazardous areas as follows:

a) Pipe the drains from each separate area to a catch basin in that area. This facilitates cleanup of minorspills within that area and minimizes the impact on the overall system.

b) Pipe the area catch basin overflow pipes into the main drainage system through manholes to facilitateinspection and cleaning.

c) Arrange the main drain or sewer pipe to discharge to a separator tank, retention basin, or otherappropriate waste treatment process located at a safe distance from important facilities to minimize fireexposure.

d) Locate the catch basins in each area in open sections of the protected area and away from importantequipment and structures to minimize fire exposure.

e) Provide traps or seals on all inlets to the catch basins and manholes to retard flammable vapor spread.

f) Avoid connecting hazardous liquid drainage systems to drains from non-hazardous locations. Vaporshave been known to travel in drainage systems into areas with unrestricted ignition sources, causing fireand explosion.

Refer to Figure 4 for examples of a typical drainage system for a multi-unit outdoor facility.

In Figure 4 pitched floors are used to create drainage high spots to direct spilled liquid from beneath impor-tant vessels, increase the liquid depth or head over drains to maximize the flow from each drain, and reducethe surface area of burning liquids to facilitate extinguishment with foam or dry chemical.

Smaller, separate drainage areas with individual drains are provided at specialized equipment or opera-tions that may have a higher frequency of spills, such as pump that may develop packing leaks.

2.2.3.6.5 Design catch basins to facilitate cleaning and to contain small routine spills.

Figure 5 shows one possible design for an inlet catch basin. The elbow on the intake outlet is removableto facilitate cleaning pipe feeding from drains. The elevation difference between the inlet and outlet pipes helpsto retard flammable vapor spread. Small quantities of unignited, spilled liquids, not involving high fire pro-tection system water flows, may be contained in the catch basins to be removed with air operated pumps orother fire safe means without contaminating the entire drainage system during a routine spill.

2.2.3.6.6 Use catch basins with a dry box design similar to that shown in Figure 6 near fired heaters, suchas hot oil furnaces, to collect spilled fuel oil, heat transfer oil, etc. These are arranged with separate drainsthrough a sealed outlet into the drainage system. This prevents accumulation of liquids beneath a potentialignition source.

2.2.4 Alternatives to Drainage

The fire exposure at some facilities may not justify the cost of installing a complete drainage system. Otherproperties, such as those located in urban areas or modern industrial parks, may lack the space neededfor large drainage systems. Local ordinances may prohibit outdoor drainage in some areas.

Where drainage installations are impractical, consider other alternatives that could reduce the flammableliquid hazard to minimize the fire exposure to important facilities. Refer to the flammable liquid use and stor-age data sheets, such as Data Sheet 7-29, Flammable Liquid Storage in Portable Containers, for specificguidance.



Fig. 4. Typical drainage system for a multi-unit outdoor facility.

Fig. 5. Sealed inlet catch basin.



2.2.4.1 Eliminate the use of flammable liquids by substituting less hazardous materials. For example, useof water based paints has replaced oil based paints in many applications. This frequently results in other ben-efits, such as reduced costs for electrical installations, hazardous waste disposal, ventilation systems, etc.

2.2.4.2 Reduce the flammable liquid inventory by purchasing materials in smaller quantities. Although use ofliquids from 55 gal (210 dm3) drums usually results in a lower cost per gallon, use of small metal containerswould result in minimal increased cost where the annual liquid use is only a few drums.

2.2.4.3 Provide FM Approved flammable liquid storage cabinets where storage rooms with drainage areimpractical for small flammable liquid users, such as laboratories.

2.2.4.4 Store flammable liquids outdoors and pump the liquid to the point of use with a piping system arrangedin accordance with Data Sheet 7-32, Flammable Liquid Operations. However, this will not eliminate the needfor drainage at the point of use if the liquid is pumped into any vessel which has a significant holdup. Forsmall quantities where an outdoor tank is not practical, a single drum stored outdoors can be equipped witha remote control air operated drum pump.

2.2.4.5 Install an automatic fixed fire protection system, such as foam (aqueous film-forming [AFFF], or highexpansion), dry chemical, or gaseous suppression.

Except for AFFF, these systems should supplement automatic sprinkler protection, not replace it.

2.2.4.6 Relocate storage, dispensing, or use of flammable liquids to low value diked structures located asafe distance from all important facilities. Size the dike to contain the anticipated spill and waterflow from firedepartment hose streams. This will minimize damage if the fire department prefers to allow the liquids toburn in the event of a fire.

2.2.4.7 Relocate storage to a detached, prefabricated Approved storage building for flammable and combus-tible liquids (See the Approval Guide, a publication of FM Approvals).

2.2.4.8 For non-critical or low-valued areas, relocate storage to a small cutoff room with total containment.

2.3 Operation and Maintenance

2.3.1 Conduct acceptance tests of new or renovated drainage installations to assure effective performanceas follows:

Fig. 6. Dry box catch basin.



a) Where possible, such as at outdoor areas protected with open-head deluge systems, test new sys-tems with a water flow equal to the maximum expected water flow during a fire.

b) Where large water flows are not possible, such as in indoor storage rooms, use the maximum practicalflow from hoses to assure adequate floor pitch, drain capacity, etc.

2.3.2 Keep floor drains, trenches, and wall scuppers clear of obstructing material.

2.3.3 Remove liquids from drainage system retention basins, tanks, etc. as needed to assure adequateretention capacity.

2.3.4 Include drainage systems in monthly inspections of fire protective equipment. Pay particular attentionto:

a) Storage on top of drains or trenches that will reduce the flow capacity.

b) Floor drain or trench grating openings plugged by spilled viscous liquids.

c) Wall scuppers stuffed with rags to prevent drafts or blocked by snow banks.

d) Damaged trench gratings that may result in lift truck accidents and subsequent property damage.

e) Valves in drainage system piping that are not in the proper normally open or shut position.

f) Accumulations of surface and rainwater in drainage system containment ponds, basins, or tanks.

2.3.5 Flow water through drainage system piping at least semiannually to ensure it is open and to flush outdebris.

3.0 SUPPORT FOR RECOMMENDATIONS

3.1 Comments on Recommendations

Provision of emergency drainage is an integral part of adequate flammable liquid protection. Other FM Globalstandards providing specific guidance for the protection of flammable liquid storage and/or processing occu-pancies have the explicit or implicit presumption that adequate drainage is provided when needed.

Drainage is needed in areas where flammable liquids are present for five reasons:

1. To prevent flammable liquid fires. Flow of unignited liquids from well arranged flammable liquid areasinto unsafe areas can cause a fire.

2. To help extinguish a fire by removing the fuel. Automatic sprinklers or water spray can extinguish firesin liquids having flash points above 200°F (93°C), in liquids soluble in water, in liquids heavier than water, andin viscous, low flash point materials. Fires in other flammable liquids must be extinguished with special firesuppression agents or by removing fuel through drainage.

3. To minimize fire spread by preventing flow of burning liquid to areas exposing other equipment or facilities.

4. To reduce fire severity. FM Global Research fire tests for protection of multilevel flammable liquid processstructures found that three dimensional spill fires create a more severe fire exposure than floor spill fires.Curbs and drains prevent vertical flow to lower levels.

5. To protect the environment from release of potentially hazardous materials. Public fire departments maywithhold fire fighting efforts where environmentally sound drainage is not provided.

From a fire protection perspective, drainage is needed where substantial quantities of flammable liquid canbe released.

For high flash point or water soluble liquids, containment alone may be sufficient to prevent fire spread untilsprinklers extinguish the fire. For low flash point liquids, drainage should be aimed at removal of the fuelwhile automatic sprinklers cool and protect the structure and equipment.

Use Figure 1 to determine when containment without drainage is acceptable.



3.2 Loss History

During the eleven year period from 1977 to 1988 FM Global recorded approximately 56 flammable liquidfires where drainage was a factor1. Excluding six large losses where the lack of many additional automaticsprinklers was also a major factor, the average loss was $345,000 per fire2.

Principal causes of these fires were electric equipment, gas burners, cutting and welding, overheating, spon-taneous ignition, electric heaters, and hot pipes. Although drainage will reduce the damage from a fire, igni-tion sources must be controlled to reduce the frequency of fires in flammable liquid occupancies asrecommended in other data sheets.

Other factors that contributed to these losses included: lack of automatic sprinklers, inadequate flammableliquid control or containment, unsafe operator procedures, undersized relief vents, lack of damage-limitingconstruction, failure of fixed fire extinguishing systems, poor housekeeping, inadequate Emergency Orga-nization (EO), lack of high-level interlocks on storage tanks, inadequate ventilation, and non-Approved elec-tric lift trucks.

3.3 Illustrative Losses

3.3.1 Paint Distribution Center Destroyed

Flammable liquids in small containers were stored in racks and on the floor in a 180,000 ft2 (16,720 m2)warehouse. Fire protection was provided by wet-pipe ceiling and in-rack sprinklers, fed by a 2,500 gpm (9,465dm3/min) booster fire pump. Employees were trained to use hose stations and portable fire extinguishers.

The steel-frame structure had tilt-up concrete walls and a steel deck roof. A self-supporting, nonload-bearing,four hour fire resistant fire wall divided the warehouse into 98,600 (9,160 m2) and 82,000 ft2 (7,620 m2) sec-tions. Vehicle and personnel openings in the center wall had fire doors but were not protected with curbs,ramps or drainage trenches.

Sparks from a non-Approved lift truck ignited a spill of about 8 to 10 gal (30 to 38 dm3) of flammable liquids.Despite prompt action by employees and proper operation of automatic sprinklers, the fire engulfed thewarehouse. Product flowing under closed fire doors carried the fire through the center fire wall to involve theentire warehouse.

Although extensive damage to the warehouse was likely due to the extreme fire hazard, rapid initial fire spreadand inadequate sprinkler protection, trenches or curbs at fire doors might have confined the fire to one area.Drainage to a safe location may have allowed the fire department to protect the exposed half of the build-ing. Estimated loss $49 million (1987)3.

3.3.2 Farm Supply Warehouse

An unsprinklered, one story, metal panel on steel frame structure was destroyed by a fire ignited by anoverheated well pump motor. The building was used for storage and sales of farm supplies, includingfertilizers, pesticides, kerosene, and herbicides. The local fire department was familiar with the property’scontents.

The fire department responded to the warehouse to investigate an odor of smoke. The arriving fire chiefsaw smoke and heard the crackling of fire within the chemical storage area. An almost immediate decisionwas made that fighting the fire would be out of the question due to the fear of contaminating the environ-ment. It was decided to let the building burn.

This loss illustrates a tactic that some fire departments may choose when they fear that fighting a fire couldcontaminate ground water or streams. Similar losses could be prevented by storing flammable liquids in build-ings with proper drainage. If this is impractical, storage of flammable liquids in detached, low value build-ings would minimize damage if free burn tactics are used. Estimated loss $1.5 million (1986).

1 At facilities insured by FM Global.2 Dollar values indexed to 1990.3 Not insured by FM Global.



4.0 REFERENCES

4.1 FM Global

Data Sheet 1-24, Protection Against Liquid Damage.

Data Sheet 3-0, Hydraulics of Fire Protection Systems.

Data Sheet 5-4, Transformers.

Data Sheet 7-2, Waste Solvent Recovery.

Data Sheet 7-9, Dip Tanks, Flow Coaters, and Roll Coaters.

Data Sheet 7-14, Fire & Explosion Protection for Flammable Liquid, Flammable Gas, & Liquefied FlammableGas Processing Equipment & Supporting Structures.

Data Sheet 7-27, Spray Application of Flammable and Combustible Materials.

Data Sheet 7-29, Flammable Liquid Storage in Portable Containers.

Data Sheet 7-30N, Solvent Extraction Plant.

Data Sheet 7-32, Flammable Liquid Operations.

Data Sheet 7-37, Cutting Oils.

Data Sheet 7-41, Heat Treatings of Materials Using Oil Quenching and Molten Salt Baths.

Data Sheet 7-43/17-2, Loss Prevention in Chemical Plants.

Data Sheet 7-57, Pulp and Paper Mills.

Data Sheet 7-77, Testing Internal-Combustion Engines and Accessories.

Data Sheet 7-88, Flammable Liquid Storage Tanks.

Data Sheet 7-93, Aircraft Hangers.

Data Sheet 7-95, Compressors.

Data Sheet 7-98, Hydraulic Fluids.

Data Sheet 7-99/12-19, Heat Transfer by Organic and Synthetic Fluids.

Data Sheet 7-101, Fire Protection for Steam Turbines and Electric Generators.

Data Sheet 8-8, Distilled Spirits Storage.

Data Sheet 9-2, Surface Water.

Approval Guide, a publication of FM Approvals.

4.2 NFPA Standards

NFPA 16, Deluge Foam-Water Sprinkler Systems and Foam-Water Spray Systems.

NFPA 30, Flammable and Combustible Liquids Code.

APPENDIX A GLOSSARY OF TERMS

Approved: references to ‘‘Approved’’ in this data sheet means the product and services have satisfied thecriteria for FM Approval. Refer to the Approval Guide, a publication of FM Approvals for a complete listing ofproducts and services that are FM Approved.

APPENDIX B DOCUMENT REVISION HISTORY

March 1991. Technical Revision.

September 1998. Reformatted.



APPENDIX C BIBLIOGRAPHY

1. Isner, Michael. ‘‘$49 Million Loss in Sherwin-Williams Warehouse Fire.’’ Fire Journal 82 (March/April 1988),NFPA

2. National Fire Protection Association. Water Spray Fixed Systems for Fire Protection. NFPA 15. Quincy,Mass: NFPA, 1982.

3. New York State Department of Environmental Conservation. Technology for the Storage of HazardousLiquids. New York: Bureau of Water Resources, New York State Department of Environmental Conserva-tion, 1983.

4. Petroleum Association for Conservation of the Canadian Environment. Bulk Plant Design Guidelines forOil Spill Prevention and Control. PACE Report No. 80-3. Ottawa, Canada: PACE Product Storage andHandling Committee, 1980.

5. Slye, O. M. Loss Prevention Fundamentals for the Process Industry. American Institute of ChemicalEngineers, Annual Loss Prevention Symposium, March 6, 1988.

6. U.S. Government. Code of Federal Regulations, Title 40, Parts 100-149. Washington D.C.: U.S.Government Printing Office.

APPENDIX D CONFLICTS WITH NFPA

NFPA 16, Foam-Water Sprinkler and Foam-Water Spray Systems, Item 4-4.7, states that drainage or reten-tion of water from sprinklers and hose and spill discharge is required with the use of foam/water systems.

A conflict exists between NFPA 16 and this data sheet. Item 2.1.4 recommends containment only where afoam/water system is provided instead of a water suppression system. Although installation of drainage andcontainment may be advantageous, a properly designed foam/water system is expected to extinguish a fire.

NFPA 30, Flammable and Combustible Liquids Code, also addresses the need for drainage and containment.There is no conflict between this data sheet and NFPA 30.



Documents

Drainage Systems for Flammable Liquids