IS 15105:2021 – Fire Sprinkler Design Standard | Spacing, Density & Installation

IS 15105:2021 – Fire Sprinkler Design Standard (India)

Design, Installation and Maintenance of Fixed Automatic Sprinkler System

IS 15105:2021 is the Indian Standard issued by the Bureau of Indian Standards (BIS) that specifies the minimum requirements for the design, installation, and maintenance of fixed automatic sprinkler systems in buildings.

This standard applies to sprinkler systems used for the protection of life and property across a wide range of occupancies, including industrial, commercial, residential, and storage buildings.

Scope of the Standard

The standard covers:

Design criteria for sprinkler systems
Installation requirements
Hydraulic calculation methods
Water supply and pumping capacity requirements
Hazard classification of occupancies
Storage commodity categorization
Requirements for high-rise buildings
Guidelines for ESFR, Large Drop, and in-rack sprinklers
Documentation and drawing requirements
Maintenance provisions to ensure system reliability

The provisions are applicable to:

New installations
Additions or extensions to existing sprinkler systems
Modifications or repairs to installed systems

What is NOT Covered

This standard does not apply to:

Water spray systems
Deluge systems (covered under IS 15325 and IS 15519)
Marine, aircraft, vehicle or mining sprinkler applications

Design Philosophy

IS 15105 emphasizes:

Proper hazard classification (Light, Ordinary, High, Storage)
Hydraulic calculation for high hazard systems
Enhanced storage protection requirements
Adoption of modern sprinkler technologies such as ESFR
Integration of sprinkler systems with overall fire protection strategy

The 2021 revision strengthens hydraulic design requirements and aligns Indian practice closer to international standards.

🔥 Types of Sprinklers

Alarm Valve

An alarm valve is a specially designed check valve installed in a sprinkler system that allows water to flow into the system when a sprinkler operates and simultaneously initiates an alarm signal.

When water flows through the valve due to sprinkler activation, it operates an alarm device such as:

A water motor gong (mechanical alarm), and/or
An electric pressure switch connected to the fire alarm system.

Each type of sprinkler system (wet, dry, deluge, pre-action) incorporates a suitable alarm valve arrangement to ensure that water flow during fire conditions is automatically detected and signaled.

The alarm valve also permits system monitoring through upstream and downstream pressure gauges and includes provisions for alarm testing.

Main Elements of a Sprinkler Installation

🔹 Key Components

Installation Control Valve Set
Includes the alarm valve and stop valve. It controls water supply to the sprinkler system and initiates alarm when water flows.
Main Distribution Pipe (Feed Main)
Primary pipe that distributes water to different distribution pipes.
Distribution Pipe (Cross Main / Destination Pipe)
Supplies water to branch (range) pipes.
Range Pipe (Branch Pipe)
Pipes feeding individual sprinklers directly or through arm pipes.
Arm Pipe
Short pipe (generally less than 300 mm) connecting range pipe to sprinkler head.
Riser
Vertical pipe supplying water to upper levels.
Sprinkler Head
Heat-activated device that discharges water when fire is detected.
Design Point
Reference point used in hydraulic calculations (especially in pre-calculated systems).
Drain Valve with Plug
Used for draining and testing the system.

🔹 Working Principle (Simple Flow Path)

Water Supply → Control Valve Set → Main Distribution Pipe → Distribution Pipe → Range Pipe → Sprinkler Head

When a sprinkler operates, water flows through the alarm valve, triggering an alarm.

Range Pipe Arrays in Sprinkler Systems

The figure shows different configurations of range (branch) pipes connected to distribution pipes in a sprinkler installation. These layouts affect hydraulic performance and water distribution.

1️⃣ 2- End-Side Array (Central Feed)

Range pipes provided on one side only of the distribution pipe.
Water fed from central point.
Used in narrow areas or where layout is restricted.

2️⃣ 3-End-Side Array (End Feed)

Range pipes on one side.
Water supply connected at one end of distribution pipe.
Simpler layout but higher friction loss at far end.

3️⃣ 3-End-Centre Array (Central Feed)

Range pipes on both sides of distribution pipe.
Supply from centre.
More hydraulically balanced.
Common in large open floor areas.

4️⃣ 2-End-Centre Array (End Feed)

Range pipes on both sides.
Supply from one end.
Requires careful hydraulic calculation for pressure drop.

Engineering Importance

Layout selection impacts:
- Hydraulic calculations
- Pressure loss
- Number of operating sprinklers
- Design area performance
End feed systems generally require higher pressure at remote points.
Central feed systems provide better pressure balance.

Sprinkler Network Layouts

This figure illustrates different sprinkler spacing patterns and piping network arrangements used in sprinkler system design.

3A – Rectangular Matrix Layout

Sprinklers arranged in straight rows and columns.
Equal spacing in both directions.
Most commonly used layout.
Easy for hydraulic calculations.
Suitable for standard hazard occupancies.

S = Distance between sprinklers in one direction
D = Distance between sprinklers in the other direction

3C – Looped Layout

Cross mains interconnected.
Water can reach sprinklers from more than one direction.
Reduces pressure loss.
More hydraulically reliable than simple tree systems.

3B – Staggered Layout

Alternate rows offset by half spacing.
Provides more uniform water distribution.
Improves coverage efficiency.
Often used where better spray overlap is required.

3D – Gridded Layout

Branch lines interconnected forming grid pattern.
Water supplied from multiple paths.
Provides best hydraulic balance.
Suitable for large floor plates and high hazard areas.

Engineering Significance

Requirements Regarding Documentation

IS 15105 specifies that proper drawings and documentation must be submitted for approval before installation of a sprinkler system.

General Drawing Requirements

Drawings must be clear, dated, and to scale.
Scale generally: 1:500 or 1:1000 (site plans).
For installation layout: not less than 1:100.
Digital copies are acceptable if approved.
Drawings must show:
- Entire compound
- All buildings
- Future extensions (if any)
- Boundary walls

Details to be Shown on Drawings

Building Information

Fire walls, fire doors, shutters
Construction type (masonry, steel, etc.)
Floor areas and elevations
Ceiling heights
Concealed spaces

Sprinkler System Details

Complete sprinkler layout
Pipe sizes and routing
Type of sprinklers
Temperature rating
K-factor
Number of sprinklers per control valve
Height of highest sprinkler
Location of alarm valves
Drain valves and test valves

Water Supply Details

Pump capacity and head
Pump house layout
Suction and delivery piping
Water tank capacity and compartmentation
Overflow and freeboard levels
Electrical supply to fire pumps

Hydraulic Calculation Requirements

For Fully Hydraulic Systems, documentation must include:

Design density (mm/min)
Design area (m²)
Assumed Maximum Area of Operation (AMAO)
Sprinkler K-factor
Flow through each sprinkler
Pressure at each node
Pipe sizes
Pipe lengths
Equivalent lengths of fittings
Hazen-Williams coefficient
Static head changes
Friction loss calculations
Pressure-flow graph of water supply

Mandatory Declaration

A statement confirming:

The system complies with IS 15105:2021, including any deviations with justification.

Why Documentation is Important

Ensures regulatory approval
Verifies hydraulic balance
Confirms adequate water supply
Provides reference for maintenance
Prevents under-designed systems

Classification of Occupancies

The sprinkler system design depends on the fire load, combustibility, and fire growth potential of the occupancy. IS 15105 classifies occupancies into four main categories.

Classification of Occupancies – Typical Examples

Classification of Occupancies - Examples

List of Occupancies under Different Classes

Storage Hazards

PLANNING STAGE

The planning stage ensures proper integration of the sprinkler system with building design, water supply, and other fire protection measures.

1️⃣ Initial Considerations

2️⃣ Outline Design Considerations

3️⃣ Interaction with Other Fire Protection Systems

4️⃣ Extent of Sprinkler Protection

5️⃣ Exceptions (Where Sprinklers May Not Be Required)

Planning Stage – Key Objective

✔ Correct hazard classification
✔ Adequate water supply
✔ Proper integration with building design
✔ Avoid conflicts with other fire systems
✔ Ensure long-term maintainability

Protection of Concealed Spaces

Height Difference Between Highest & Lowest Sprinklers

SPRINKLERS – General Requirements

1️⃣ General Provisions

2️⃣ Selection of Sprinklers

Sprinklers shall be selected based on:

Occupancy hazard classification
Storage configuration (if applicable)
Ceiling height
Type of sprinkler system (wet, dry, etc.)
K-factor requirements
Temperature rating

3️⃣ Installation Requirements

Sprinklers must be installed in correct orientation (pendent/upright/sidewall).
Installed as per spacing and positioning rules of the standard.
Must comply with approved listing and manufacturing standards.
Only listed sprinklers for special applications (e.g., concealed spaces) shall be used.

4️⃣ K-Factor Requirement

Selection of Temperature Rating for Sprinklers

Sprinklers operate when the thermal element reaches its rated temperature. The correct temperature rating must be selected based on the maximum expected ambient ceiling temperature.

Typical Selection Guidance

Temperature Rating for High Piled Storage

1️⃣ High Hazard – High Piled Storage

2️⃣ Glazed Roof or PVC / Plastic Roofing Sheets

3️⃣ Near Ovens or Hot Process Hoods

4️⃣ Clearance from Hot Sources

Because sprinklers are heat sensitive:

Must be located minimum 750 mm to 2000 mm away from hot sources
Distance depends on ambient temperature conditions

🔥 Key Engineering Insight

High piled storage produces:

Rapid fire growth
High ceiling jet temperatures

Therefore:
✔ Higher temperature rating prevents premature activation
✔ Ensures correct sequence of sprinkler operation
✔ Avoids unnecessary system discharge

Mixing of Different Types of Sprinklers

🔹 General Rule

Different types of sprinklers shall not be used in the same hazard area, unless specifically justified and approved.

Mixing different sprinkler characteristics can result in:

Uneven water distribution
Hydraulic imbalance
Improper fire control performance

🔹 The Following Shall Be Avoided

🔥 Engineering Principle

A sprinkler system must operate as a uniform hydraulic and thermal unit.
Mixing types within the same hazard area may cause:

Delayed suppression
Over-discharge in some areas
Under-protection in remote areas

Protection to the Sprinklers

🔹 General Requirement

Sprinklers shall be installed and protected so that their operation, discharge pattern, and sensitivity are not impaired by mechanical damage, corrosion, or environmental conditions.

🔹 Mechanical Protection

🔹 Corrosion Protection

🔹 Installation Protection

Sprinklers shall not be obstructed.
Guards or protective devices shall not interfere with water distribution.
Only manufacturer-approved protective devices shall be used.

🔥 Objective of Clause 7.9

✔ Ensure sprinkler reliability
✔ Prevent accidental damage
✔ Maintain proper spray performance
✔ Preserve thermal sensitivity

Spare Sprinklers to be Kept in Stock

A stock of spare sprinkler heads shall be maintained on the premises to enable prompt replacement of operated or damaged sprinklers.

Design Area and Density of Application

1️⃣ Light Hazard (LH)

2️⃣ Ordinary Hazard (OH)

🔸 Storage in OH Occupancy (Allowed Only If):

📦 Maximum Storage Heights in OH (Table 6)

3️⃣ High Hazard (HH)

4️⃣ Storage Hazard

Density depends on:

- Sprinkler type selected

- Flow & pressure requirements

Typical Density Range: 25 – 50 lpm/m²

Refer to Annex C for detailed design criteria.

ANNEXURE - C (GUIDELINES FOR THE PROTECTION OF STORAGE AREAS) - ESFR SPRINKLER INSTALLATION

Buildings Like Residential, Hotels & Similar

Buidling like residential and hotels-Photoroom

🔥 Quick Comparison Table

Engineering Insight

Density = Fire control capability
Design Area = Assumed Maximum Area of Operation (AMAO)
Density shall never be reduced even if actual compartment is smaller
Storage design is significantly more demanding

Design Area and Density of Application

This clause defines how the design area is determined when using special types of sprinklers.

1️⃣ Extended Coverage (EC) Sprinklers

2️⃣ Large Drop (LD) Sprinklers

3️⃣ ESFR Sprinklers

4️⃣ Intermediate (In-Rack) Sprinklers

🔥 Engineering Insight

EC sprinklers → Larger spacing → Larger design area
Large Drop → Control mode → Rectangular demand area
ESFR → Fixed 12-sprinkler calculation
In-rack → Based on rack geometry & aisle width

Adjustment in Area of Operation (Design Area)

This clause specifies when the design area (AMAO) must be increased or reduced based on system and building conditions.

1️⃣ Sloping Roofs

2️⃣ Dry Pipe & Double Lock Pre-Action Systems

3️⃣ High Temperature Sprinklers (High Hazard)

Adjustment in Area - High Temp Sprinkler

4️⃣ Multiple Adjustments

If more than one condition applies:

Adjustments shall be compounded
Based on original design area specified in 8.1

Example:
If both sloping roof and dry system apply →
Area = Base Area × 1.3 × 1.3

5️⃣ Concealed Spaces

Concealed spaces (combustible or non-combustible) follow the same adjustment rules
Exception: If concealed space area < 5 m², adjustment not required

🔥 Quick Summary Table

Engineering Insight

Area adjustment compensates for:
Slower activation
Water delivery delay
Ceiling jet behavior changes
Thermal lag in high temperature sprinklers
Density remains unchanged — only the assumed operating area is modified.

Water Curtain Sprinklers

Water curtain sprinklers are used to create a water barrier (blanket effect) across openings to prevent fire spread between compartments.

🔹 Performance Requirements

🔹 Design Considerations

Water curtain sprinklers are typically:

Open type nozzles
Used for fire separation
Installed over openings

Water supply for curtain sprinklers:

Shall be added to main system demand
As per Clause 13 (Water Supply Requirements)

🔹 Important Notes

Engineering Purpose

Protect openings between compartments
✔ Prevent horizontal fire spread
✔ Provide water shield across glass walls or large openings
✔ Used where fire walls are not feasible

Exposure Protection

Exposure protection sprinklers are used to protect building surfaces (such as glass walls or openings) from fire exposure originating from adjacent structures or areas.

🔹 General Requirements

🔹 Protection Limits

Exposer protection - protection limit-Photoroom

🔹 Glass Wall Protection

Exposer protection - glass wall-Photoroom

🔹 Window & Similar Openings

Exposer protection - window opening-Photoroom

Sprinklers Provided in Ducts

Window Sprinklers

Window sprinklers are specially listed sprinklers used for interior protection of windows or glazing and for exposure protection.

Design Approach – Spacing, Location and Installation

🔷 Key Design Considerations

Clause 9 lays down the fundamental principles for the layout, spacing, positioning, and installation of sprinklers to ensure effective fire control and uniform water distribution.

🔷 Maximum Area to be Covered by Sprinklers

Max Area covered by Sprinkler System Riser

🔷 Vertical Change in Ceiling Elevation (Less Than 900 mm)

🔷 Vertical Change in Ceiling Elevation (Less Than 900 mm)

🔷 Sprinklers Below Obstructions

Sprinklers Below Ducts

Sprinklers shall be installed below ducts in the following situations:

Where ducts are rectangular and more than 0.8 m wide, and located less than 150 mm from adjacent walls or partitions.
Where ducts are circular and more than 1 m in diameter, and located less than 150 mm from adjacent walls or partitions.
Where ducts are rectangular and more than 1 m in width.
Where ducts are circular and more than 1 m in diameter.

Movable Obstructions

Sprinklers are not required under movable obstructions such as:

Conference tables
Similar movable furniture

Hoods Over Paper Making Machines

Sprinklers shall be installed:

Under hoods or shields
Over dry ends of paper making machines
Where an enclosure exists

Worktables

Sprinklers shall be installed below worktables:

Where a power source exists, or
Where combustible process waste may accumulate

(Applicable to industrial and storage occupancies only.)

Important Note

Sprinklers installed below obstructions shall be of the same type as the ceiling sprinklers.

🔷 Sprinkler Location Below Ceilings

🔷 Positioning of Sprinklers to Avoid Obstruction to Discharge

🔷 Standard Sidewall Sprinklers

🔹 Protection Area

🔹 Maximum Distance Between Sprinklers

Spacing shall be measured along the slope of the ceiling.
Maximum spacing:
- 4.3 m for Light Hazard
- 3.0 m for Ordinary Hazard
Sidewall sprinklers shall not be installed back-to-back unless separated by a continuous lintel or soffit.
They may be installed on opposing or adjacent walls provided no sprinkler exceeds its permitted protection area.
When installed on two opposite walls or sides of bays:
- Maximum room width: 7.3 m (High Hazard)
- 6.1 m (Ordinary Hazard)

🔹 Minimum Distance Between Sprinklers

Minimum centre-to-centre spacing: 1.8 m
Distance from wall shall be measured perpendicular to the wall.

🔹 Maximum Distance from Walls

End sprinklers shall not exceed half of the allowable distance between sprinklers.

🔹 Minimum Distance from Walls

Minimum distance from wall: 100 mm
Distance measured perpendicular to the wall.