Designing a sprinkler system for warehouses, retail stores, or industrial facilities?
Then you MUST understand how NFPA 13 defines commodity classes β and how sprinklers protect them! π§Ά
Sprinkler systems aren’t just about spraying water β they’re about delivering the right amount of water, at the right time, to the right place.
Without understanding what youβre protecting, you risk undersizing (which is dangerous!) or oversizing (which is wasteful!). π‘
β¨ Understanding Storage Protection Under NFPA 13
What is ‘Storage Protection’?
When we talk about “storage protection”, we mean selecting and designing sprinkler systems based on what is stored. Different goods ignite, burn, and spread flames at different speeds. π₯
Therefore, the type of commodities inside a building determines:
βHow much water is needed
π§What type of sprinklers are used
π°How sprinklers are spaced and installed
Two major things matter most:
π·οΈThe Commodity Class (Class I, II, III, IV, or Plastics)
Pick a simple description. Weβll place a pin on a notional risk bar (for intuition onlyβalways verify in NFPAΒ 13).
Tip: The pin moves right as potential heat release & water demand trend upward.
Intuition toolNot a classification
β οΈ Common Pitfalls When Designing Storage Protection
Occupancy hazard (Light/Ordinary/Extra) isnβt the same as storage commodity class. Storage protection uses commodity + arrangement; donβt mix frameworks.
Rack vs solidβpile vs bin box can change required sprinkler type, spacing, and densities dramaticallyβeven for the same commodity.
Undersizing is unsafe; oversizing wastes cost and may trigger unnecessary upsizing of pumps and tanks. Start with correct classification, then select the right curve.
π§ 90βSecond MiniβQuiz
1) Which two inputs drive storage protection decisions the most?
2) For the same commodity, which factor often changes the design curve?
3) βPlastics (Group A)β generally trend toward β¦
This quiz is for learning reinforcement only; always consult the applicable NFPA 13 edition.
π Reference note: Always confirm criteria in the latest NFPAΒ 13 edition adopted by your jurisdiction. If you list clause references here, theyβll be autoβhighlighted by this widgetβs style.
π Key Terminologies Explained
π¦ Commodity
The goods or materials being stored, like clothing, electronics, furniture.
π₯ Class I to IV
A way NFPA 13 groups goods based on how easily they catch and spread fire.
𧴠Group A Plastics
Highly flammable plastics that ignite fast and burn hotter than wood or paper.
π CMSA/ESFR Sprinklers
Special sprinkler types designed to control or suppress intense storage fires quickly.
π NFPA 13 Commodity Classifications
ποΈ Class I Commodity
Noncombustible products placed on wood pallets or packaged in cardboard.
Examples: Canned foods, glassware, bottled water.
π Minimal packaging means lower fire risk.
ποΈ Class II Commodity
Noncombustible items, but with slightly heavier combustible packaging.
Examples: Books packed tightly in heavy cartons, ceramics packed with paper filler.
ποΈ Class III Commodity
Ordinary combustibles: wood, paper, fabrics.
Allows a little plastic (no more than 5% by weight).
Examples: Wooden furniture, clothing in boxes, cardboard-packed linens.
ποΈ Class IV Commodity
Goods made from or packed with more plastics (between 5% and 15%).
Might include Group B plastics too (medium fire risk plastics).
Examples: Metal furniture with plastic covers, toys packed with foamed plastic.
π Group A Plastics
β‘ Super combustible materials: they burn hotter, faster, and produce more smoke.
π Important: Group A plastics require very special sprinkler designs!
π° How Sprinkler Protection is Decided
According to Chapter 20 of NFPA 13, protection follows these key steps to create a personalized safety shield tailored to your storage risk! π‘οΈπ«΅
β Identify the Commodity Class
β Determine the Storage Method (rack, pile, bin, etc.)
β Assess Storage Height and Building Construction
β Select the Correct Sprinkler Type (Standard, CMSA, or ESFR)
β Design for Water Density, Area of Operation, and Water Supply
β Add Allowances for Fire Hose Streams if Required
π Important Tables from NFPA 13
π Table 20.9.4.2 β What It Means (Explained Simply)
βΆοΈ Table Title:Maximum Clearance from Top of Storage to Ceiling for CMDA Protection Criteria
π‘ What the Table is About:
This table tells you how much empty space you should leave between the top of stored goods and the ceiling when using CMDA sprinklers (Conventional Mode Density Application sprinklers).
π It’s about how close storage can be to the ceiling before it becomes unsafe or requires a different design!
π§Ή Breaking Down Each Row:
Storage Type
Class I to IV Commodities
Group A Plastics
Palletized, solid-piled, bin box, shelf, or back-to-back shelf storage
20 ft (6.1 m)
20 ft (6.1 m)
Rack storage up to 25 ft (7.6 m)
20 ft (6.1 m)
10 ft (3.0 m)
Rack storage > 25 ft (7.6 m)
10 ft (3.0 m)
10 ft (3.0 m)
π§ What Each Storage Condition Means:
Palletized / Solid-Piled / Shelf Storage: Goods stacked without high racks. β 20 ft (6.1 m) clearance allowed for both Class I-IV and Group A Plastics.
Rack Storage up to 25 ft: β 20 ft clearance for Class I-IV. β οΈ Only 10 ft (3.0 m) for Group A Plastics.
Rack Storage over 25 ft: β Always 10 ft (3.0 m) clearance, no matter the material.
π― In Summary:
π§Ί Simple pile storage? 20 ft clearance is OK for everything.
ποΈ High-risk plastics in racks? β 10 ft clearance needed!
π Very tall racks? β Always keep 10 ft clearance, no exceptions.
β¨ Why Is This Important?
If the gap is too big, fire can grow uncontrolled before sprinklers react.
A smaller gap allows sprinklers to catch the fire faster, reducing damage and saving lives! π‘οΈ
π Important Tables from NFPA 13
π Table 20.9.4.3 β Class I Through Class IV Commodities (Explained Simply)
βΆοΈ Table Title:Clearances and In-Rack Sprinkler Options for Storage
π‘ What the Table is About:
This table tells you how to handle fire protection when thereβs a large gap between the top of stored goods and the ceiling, especially for Class I-IV commodities.
π It also explains when in-rack sprinklers are permitted as an alternative solution to ceiling-only sprinklers!
π§Ή Breaking Down Each Row:
Storage Configuration
When Clearance to Ceiling Exceeds
Protection Based on Clearance of…
In-Rack Sprinklers
Palletized, solid-piled, bin box, shelf, or back-to-back shelf storage
20 ft (6.1 m)
20 ft (6.1 m)
N/A
Rack storage up to and including 25 ft (7.6 m)
20 ft (6.1 m)
20 ft (6.1 m)
Permitted as alternative
Rack storage over 25 ft (7.6 m)
10 ft (3.0 m)
10 ft (3.0 m)
Permitted as alternative
π§ What Each Storage Configuration Means:
Palletized / Solid-Piled / Shelf Storage: β Clearance within 20 ft (6.1 m) β No in-rack sprinklers needed.
Rack Storage up to 25 ft: β Clearance more than 20 ft β Can either redesign or use in-rack sprinklers.
Rack Storage over 25 ft: β Clearance more than 10 ft β In-rack sprinklers are a smart and sometimes necessary choice.
π― Key Takeaways:
π§Ί Small gaps = OK with ceiling sprinklers alone.
ποΈ Large gaps = β In-rack sprinklers may be needed!
π In-rack sprinklers supplement ceiling systems for better early fire control.
β¨ Important Note:
When using in-rack sprinklers: Install a sprinkler layer directly under the top tier of storage and at every flue space intersection for maximum protection! π₯
π Important Tables from NFPA 13
π Table 20.9.4.4 β Plastics and Rubber Commodities (Explained Simply)
βΆοΈ Table Title:Clearances and In-Rack Sprinkler Options for Plastics and Rubber Storage
π‘ What the Table is About:
This table explains how to manage fire protection for plastics and rubber goods, which burn much faster and hotter than typical materials.
π It shows when you must add in-rack sprinklers or adjust your sprinkler system depending on storage type and height!
π§Ή Breaking Down Each Row:
Storage Configuration
When Clearance to Ceiling Exceeds
Protection Based on Clearance of…
In-Rack Sprinklers
Palletized, solid-piled, bin box, shelf, or back-to-back shelf storage
20 ft (6.1 m)
20 ft (6.1 m)
N/A
Rack storage up to and including 25 ft (7.6 m)
10 ft (3.0 m)
10 ft (3.0 m)
Permitted as alternative
Rack storage over 25 ft (7.6 m)
10 ft (3.0 m)
N/A
Required
π§ What Each Storage Configuration Means:
Palletized / Solid-Piled Storage: β 20 ft (6.1 m) clearance allowed β No in-rack sprinklers needed.
Rack Storage up to 25 ft: β Clearance over 10 ft β Install in-rack sprinklers optionally for better protection.
Rack Storage over 25 ft: β οΈ In-rack sprinklers are mandatory because plastics burn intensely at these heights.
π― Key Takeaway:
π§Ί Low storage β Ceiling sprinklers only.
ποΈ Medium height β In-rack sprinklers suggested.
π High plastic storage (>25 ft) β In-rack sprinklers REQUIRED.
β¨ Important Note:
If in-rack sprinklers are required:
β Install quick-response sprinklers directly under the top storage tier and at every flue space intersection for maximum fire control! π₯π‘οΈ
π³ Plastics Classification Decision Tree
π Figure 20.4.8 β Plastics Classification Decision Tree (Explained Simply)
βΆοΈ Figure Title:How to Classify Plastics for Fire Protection Design
π‘ What the Decision Tree is About:
This simple decision tree helps you classify plastics for sprinkler system design based on type, packaging, and expansion risk!
π Depending on the condition (cartoned, exposed, expanded, etc.), the fire risk β and your protection design β changes dramatically!
Plastics β Group B β Protect as Class IV commodities
Plastics β Group C β Protect as Class III commodities
π Hose Stream Allowance and Water Supply Duration
π Table 20.15.2.6 β Hose Stream and Supply (Explained Simply)
βΆοΈ Table Title:How much water reserve and backup hose stream you need during a fire!
π‘ What This Table is About:
During a fire, sprinklers activate β but firefighters need backup hose streams too! ππ¦ This table explains the extra water flow and how long the water supply must last, based on your storage setup.
π§Ή How to Understand the Columns:
Commodity: What youβre protecting (plastics, tires, paper rolls, etc.)
Sprinkler Type: CMDA, CMSA, or ESFR
Sprinkler Spacing Type: Standard or Extended Coverage
Number of Sprinklers in Design Area: How many sprinklers are assumed operating
Size of Design Area: The area protected during a fire
Hose Stream Allowance: Extra water flow needed (gpm or L/min)
Water Supply Duration: How long the water must flow (in minutes)
π§ Key Takeaways:
β Small design areas (~1200 ftΒ²) β 250 gpm (950 L/min) hose stream + 60 minutes water supply.
β Larger design areas (~2400 ftΒ²) β Up to 500 gpm (1900 L/min) hose stream + 90 minutes or more!
β CMSA and ESFR systems β Typically require slightly more backup due to tougher fire hazards.
β Tire and roll paper storage β Specially large hose stream and extended water durations!
π― Practical Example:
π Protecting plastics in a warehouse?
Using CMDA sprinklers and design area is 1400 ftΒ²?
β Then β 500 gpm (1900 L/min) hose stream required β Supply must last at least 90 minutes!
β¨ Important Notes:
π CMSA and ESFR: Extra sprinklers used for obstacles don’t count toward the design area size.
π For tall buildings (β₯30 ft) or portable rack setups β Supply durations can jump to 180 minutes!
π Table 20.17.1.2(a) β CMDA Sprinkler Protection for Indoor Storage of Idle Wood Pallets (Explained Simply)
Table Title:
βΆοΈ Fire Protection Rules for Storing Idle Wood Pallets Indoors
What This Table is About:
Idle wood pallets can catch fire easily! π₯ This table tells you how to set up **Control Mode Density/Area (CMDA) sprinklers** to properly protect indoor pallet storage based on height and other factors.
π§Ή How to Read This Table:
Type of Sprinkler: Only CMDA sprinklers are considered here.
Location of Storage: Whether pallets are on the floor or on racks without solid shelves.
Nominal K-Factor: The size of the sprinkler orifice (higher K = more water flow).
Maximum Storage Height: How high pallets are allowed to be stacked.
Maximum Ceiling/Roof Height: How high the building ceiling can be.
Sprinkler Density: How much water needs to be discharged per square foot.
Areas of Operation: Size of the area that sprinklers are designed to cover in a fire event.
π§ Key Points You Should Know:
β If pallets are stacked up to 6 ft (1.8 m) high, use sprinklers with K-factor 8.0 (115) or bigger. Ceiling height up to 20 ft (6.1 m) is acceptable. Sprinkler density = 0.20 gpm/ftΒ² over 3000 ftΒ² area.
β If stacking up to 8 ft (2.4 m) high, use a slightly larger sprinkler (K-factor 11.2 or bigger). Ceiling can be up to 30 ft (9.1 m).
β For storage between 8β20 ft (2.4β6.1 m) high, even bigger sprinklers (K = 11.2 or 16.8) are needed, with ceiling height limits of 30 ft (9.1 m).
β Higher storage = higher sprinkler density required!
π― Quick Summary:
π§Ί Lower stacks (up to 6 ft) β Lower density (0.20 gpm/ftΒ²) needed.
ποΈ Higher stacks β Higher density (up to 0.6 gpm/ftΒ²) needed.
π Bigger K-factor sprinklers = Better water flow to control fires faster.
β¨ Special Notes:
β If you use sprinklers with K-factor 11.2 (160) or larger, or high-temperature-rated K-8.0 sprinklers,
the area of operation can be reduced from 3000 ftΒ² to 2000 ftΒ², making the sprinkler system more efficient!
β Always check the exact required ceiling heights and densities β higher storage and building heights demand stronger sprinkler setups!
π οΈ CMDA Sprinkler Protection for Idle Wood Pallets
π‘ What This Table is About:
Idle wood pallets can catch fire easily! π₯
This table explains how to properly protect indoor pallet storage using Control Mode Density/Area (CMDA) sprinklers β based on storage height, ceiling height, and sprinkler specifications.
π§Ή How to Read This Table:
Type of Sprinkler: β Only CMDA sprinklers considered.
Location: β Floor or rack storage (no solid shelves).
Nominal K-Factor: β Size of sprinkler orifice (higher K = more flow).
Max Storage Height: β How high pallets are stacked.
Max Ceiling Height: β How high your warehouse ceiling is.
Sprinkler Density: β Water discharged per ftΒ².
Area of Operation: β Area the sprinklers are designed to protect.
π§ Key Points You Should Know:
β Up to 6 ft (1.8 m) stacking β K-factor β₯ 8.0 β Ceiling β€ 20 ft (6.1 m) β 0.20 gpm/ftΒ² over 3000 ftΒ² area.
β Up to 8 ft (2.4 m) stacking β Larger K β₯ 11.2 β Ceiling β€ 30 ft (9.1 m).
β 8β20 ft (2.4β6.1 m) stacking β K 11.2 or 16.8 β Ceiling β€ 30 ft (9.1 m).
β Higher stacking β Higher sprinkler density required!
π― Quick Summary:
π§Ί Lower stacking (up to 6 ft) β 0.20 gpm/ftΒ².
ποΈ Higher stacking β Up to 0.60 gpm/ftΒ² needed!
π Bigger K-factor sprinklers = Better, faster fire control.
β¨ Special Notes:
β If using K 11.2 or larger (or high-temp K 8.0), you can reduce area of operation from 3000 ftΒ² β 2000 ftΒ² β making your system more efficient!
β Always verify ceiling height and density requirements β higher stacks and higher ceilings = stronger system needed!
π ESFR Sprinkler Protection for Idle Wood Pallets
π Table 20.17.1.2(c) β Explained Simply
βΆοΈ Table Title:Fire Protection Setup Using ESFR Sprinklers for Pallet Storage
π‘ What This Table is About:
Protecting idle wood pallets indoors using Early Suppression Fast Response (ESFR) sprinklers β specifying the correct K-factors, ceiling heights, storage heights, and minimum operating pressures! π
π§Ή How to Read This Table:
Type of Sprinkler: β ESFR (pendent or upright type).
Location of Storage: β Floor or open racks (no solid shelves).
Nominal K-Factor: β Sprinkler size β larger K = more water output.
Max Storage Height: β How high pallets are allowed to stack.
Max Ceiling Height: β How high the building roof can be.
Minimum Operating Pressure: β The least water pressure (psi/bar) needed at sprinkler head for activation.
π§ Key Observations:
β K14.0 (200) ESFR Sprinklers:
Stack 25 ft high under 30 ft ceilings β Needs 50 psi (3.4 bar).
Ceilings up to 32 ft β Needs 60 psi (4.1 bar).
β K16.8 (240) ESFR Sprinklers:
Stack pallets up to 35 ft under 40 ft ceilings!
Required pressures between 42β52 psi (2.9β3.6 bar).
β Higher K (22.4 and 25.2) Sprinklers: β Allow for lower pressures (as low as 15 psi!) for similar protection.
β Upright ESFR Sprinklers: β Protect up to 20 ft stacking under 30β35 ft ceilings, but may require pressures up to 75 psi!
