HVAC Psychrometric Chart Practice Questions BS EN 12845: Fixed Firefighting Systems - Engineering Requirements

BS EN 12845: Fixed Firefighting Systems

Automatic Sprinkler Systems - Design & Installation Requirements

European Standard

2020 Edition

BS EN 12845 specifies requirements for the design, installation, and maintenance of fixed firefighting systems, primarily automatic sprinkler systems.

1Fundamental Principles of BS EN 12845

Hazard Classification

BS EN 12845 classifies occupancies into hazard categories:

  • Light Hazard (LH)
  • Ordinary Hazard (OH) - Categories I, II, III, IV
  • High Hazard (HH) - Categories 1, 2, 3
  • Special Occupancy Hazards
BS EN 12845: Clause 6.2
System Types

Different system types for various applications:

  • Wet pipe systems
  • Dry pipe systems
  • Pre-action systems
  • Deluge systems
  • Tail-end systems
BS EN 12845: Clause 11

2Design Requirements & Parameters

Design Density & Area of Operation

Minimum design densities and areas of operation based on hazard classification:

Hazard Classification Design Density (mm/min) Area of Operation (m²) Minimum Pressure (bar) Standard Reference
Light Hazard (LH) 2.25 84 0.35 Table 3
Ordinary Hazard I (OH1) 5.0 72 0.35 Table 3
Ordinary Hazard II (OH2) 5.0 144 0.35 Table 3
Ordinary Hazard III (OH3) 5.0 216 0.35 Table 3
Ordinary Hazard IV (OH4) 5.0 288 0.35 Table 3
High Hazard 7.5-30.0 260-400 0.5-1.4 Table 4
Sprinkler Spacing & Location

Maximum spacing and coverage area requirements:

Hazard Classification Max Spacing (m) Max Coverage Area (m²) Distance from Walls (m) Standard Reference
Light Hazard (LH) 4.6 21 2.3 Table 19
Ordinary Hazard (OH) 4.0 12 2.0 Table 19
High Hazard (HH) 3.7 9 1.8 Table 19

3Hydraulic Calculation Requirements

Hydraulic Calculation Methodology

BS EN 12845 specifies detailed requirements for hydraulic calculations:

Parameter Requirement Standard Reference
Calculation Method Hazen-Williams formula with C=120 for steel pipes Clause 13.2.1
Flow Velocity Limits 6 m/s at valves, 10 m/s in pipes Clause 13.2.3
Accuracy Requirements Pressure balanced to ±1 mbar at junctions Clause 13.2.5.1
K-factor Tolerance ±4 for K=80 sprinklers (76-84 range) Table 37
Minimum Sprinkler Pressure 0.35 bar for OH installations Clause 13.4.4
Water Supply Requirements

Minimum water supply characteristics based on hazard classification:

Hazard Classification Flow Rate (L/min) Duration (min) Pressure (bar) Standard Reference
Light Hazard (LH) 675-945 30 1.0-1.7 Table 6
Ordinary Hazard I (OH1) 900-1260 60 1.4-2.3 Table 6
Ordinary Hazard II (OH2) 1280-1800 60 1.4-2.3 Table 6
Ordinary Hazard III (OH3) 1920-2700 90 1.4-2.3 Table 6
Ordinary Hazard IV (OH4) 2560-3600 120 1.4-2.3 Table 6

4Pipework & Installation Requirements

Pipe Sizing Requirements

Pipe sizing based on number of sprinklers and system layout:

Pipe Type Diameter (mm) Max Sprinklers Standard Reference
Last Range Pipe 25 2 Table 30
32 3
40 4
50 9
Other Range Pipes 25 3
32 4
40 6
50 9
Pipe Installation Requirements

Key installation requirements for sprinkler system pipework:

Requirement Specification Standard Reference
Pipe Materials Steel, copper, CPVC (based on hazard classification) Clause 15.2
Support Spacing Based on pipe diameter and material Table 41
Corrosion Protection Required for steel pipes in corrosive environments Clause 15.4
Drainage Minimum slope 1:200 for drainage Clause 15.5.2
Identification Pipes to be identified with safety red color Clause 15.6

5System Components & Equipment

Sprinkler Requirements

Technical specifications for sprinklers:

Parameter Requirement Standard Reference
K-factor K=80 nominal (±4 tolerance) Table 37
Orifice Size 15mm Table 37
Temperature Ratings Based on maximum ceiling temperature Clause 14.4
Thermal Sensitivity Standard or quick response based on occupancy Table 38
Positioning Deflector orientation and clearance requirements Clause 12.4
Valve Requirements

Control valve specifications and requirements:

Valve Type Requirements Standard Reference
Alarm Valve Wet, dry, or pre-action based on system type Clause 16.2
Stop Valves OS&Y gate valves with supervisory switches Clause 16.3
Check Valves Required in water supply connections Clause 16.4
Drain Valves Provided at all low points Clause 16.5
Test Valves For flow testing and alarm activation Clause 16.6

6Water Supplies & Tanks

Water Supply Requirements

Acceptable water supplies and their requirements:

Water Source Requirements Standard Reference
Gravity Tanks Minimum capacity based on hazard classification Clause 9.2.2
Pump Supplies Diesel or electric fire pumps with backup power Clause 9.2.3
Pressure Tanks Minimum water and air volume requirements Clause 9.2.4
Town Mains Dual feed preferred with reliable supply Clause 9.2.5
Open Water Screened suction with strainer Clause 9.2.6
Water Tank Requirements

Minimum water storage capacities based on hazard classification:

Hazard Classification Minimum Capacity (m³) Duration (minutes) Standard Reference
Light Hazard (LH) 18.9 30 Table 9
Ordinary Hazard I (OH1) 54 60 Table 9
Ordinary Hazard II (OH2) 108 60 Table 9
Ordinary Hazard III (OH3) 162 90 Table 9
Ordinary Hazard IV (OH4) 216 120 Table 9

7Commissioning & Maintenance

Commissioning Requirements

System commissioning and acceptance testing procedures:

Test Requirement Standard Reference
Hydrostatic Test 1.5× working pressure for 2 hours (min 10 bar) Clause 27.2.2
Flushing Thorough flushing before final connections Clause 27.2.3
Air Pressure Test For dry pipe systems: 2.8 bar for 24 hours Clause 27.2.4
Flow Tests Verification of water supplies and pump operation Clause 27.2.5
Alarm Tests Verification of all alarm and supervisory functions Clause 27.2.6
Maintenance Requirements

Ongoing inspection, testing and maintenance requirements:

Frequency Activity Standard Reference
Weekly Visual inspection of valves, gauges, and water supplies Annex E
Monthly Alarm tests, pump tests without water Annex E
Quarterly Full pump tests with water, alarm valve tests Annex E
Annually Full system inspection and test Annex E
5-Yearly Internal inspection of piping Annex E
10-Yearly Sample sprinkler operation test Annex E

8Special Engineering Considerations

Special Protection Requirements

Additional requirements for specific situations:

Situation Requirement Standard Reference
Concealed Spaces Sprinkler protection for voids > 800mm depth Clause 5.4
Rack Storage In-rack sprinklers for storage over specified heights Clause 22.2
Rolling Shutters Interlocking with fire alarm system Clause 24.3
Electrical Equipment Special extinguishing systems for high-value equipment Clause 25.2
Cold Areas Dry pipe or antifreeze systems for areas below 4°C Clause 11.1.2
Engineering Summary

Key engineering principles from BS EN 12845:

BS EN 12845 provides comprehensive requirements for the design, installation, and maintenance of automatic sprinkler systems based on hazard classification and risk assessment.
  • Hazard classification drives all design parameters
  • Hydraulic calculations must follow specified methodology
  • Component specifications are strictly defined
  • Water supplies must be reliable and adequate
  • Regular maintenance is essential for system reliability