Fire Alarm System Sound Pressure Calculation Example
Our organization has developed a fire alarm system for a shopping center.
Alarm System Calculation
The Alarm and Evacuation Control System is designed within the framework of major renovation of a shopping and entertainment center.
System Solutions
The project involves major renovation of the shopping and entertainment center.
Introduction
The project provides the following system equipment measures:
Demolition of existing control equipment, existing cable lines and speakers, and temporary demolition during roof reinforcement. During roof reinforcement period, the contractor must consider compensation measures for normal shopping center operation.
Relocation of existing alarm control equipment to low-current room.
Installation of designed cable lines and speakers.
Main technical solutions and system operation.
The facility is equipped with Alarm and Evacuation Control System type 4.
The following constant background noise levels are adopted for this facility:
- Public areas - 65 dBA
- Service and technical premises - 50 dBA
- High-noise areas in ventilation chamber - 70 dBA
- Safety corridors - 65 dBA
- Roof - 60 dBA
Notification zone feedback with security post is provided through video surveillance system, internal telephone communication and security staff mobile communication.
Alarm Equipment Selection
The system is built on existing network controller which serves as system core. Audio inputs can receive announcements from announcement stations, background music or local audio signals. The controller monitors all system equipment status, reports status changes and stores last 200 system fault messages. Existing power amplifiers and designed amplifier connect to existing network controller. One amplifier is used for roof and ventilation chamber coverage. Power amplifiers are designed for audio signal amplification and transmission to speaker lines.
Power amplifiers connect in chain to existing interface via fiber optic lines. Fiber optic lines form closed ring providing system redundancy. Amplifiers have built-in output transformers for 70V and 100V speaker operation. All equipment connection uses network cables. The project provides reserve notification lines for additional tenant equipment during renovations.
System Monitoring
Line monitoring uses supervision boards and supervision kit consisting of master and slave boards. Master board installs on amplifier channel output board, while slave board connects to last speaker in monitored line. Different monitoring boards are used for various amplifier types. Line protection against short circuits uses connection adapters.
In high-noise areas, ventilation chambers, elevator machine rooms, restrooms and accessibility areas, visual indicators are installed alongside voice notification devices. Exit signs and directional indicators are covered in electrical section. Tenant room cable line connection uses fire-resistant boxes.
Automatic system activation occurs from command pulse generated by automatic fire alarm. Command pulse from fire alarm control modules goes to announcement controller, which switches signal to amplifiers. Fire alarm signal has highest priority except emergency services signals, so during emergency messages all other signals are disabled.
Zoning Features
The designed system can organize following zones:
- Service zone
- Tenant zone
- Public zone
Programming Instructions
Contractor responsibilities include integrating newly installed equipment in renovation area into existing voice system, including necessary programming work.
Peripheral Equipment Solutions
Metal cabinet speakers are used in all premises except ventilation chamber. Horn speakers are installed in high-noise areas like ventilation chamber. Wall-mounted and horn speakers install on walls with top part at least 2.3m from floor level, but distance from ceiling to top of device at least 150mm. In rooms with height less than 2.45m, wall-mounted speakers should position with at least 0.15m from ceiling to top.
Cable Support System Solutions
Notification cable lines use fire-resistant cable. Cable routes lay in plastic rigid conduits on cable supports fixed to ceilings and walls. Cable laying follows cable support standards. Cable penetrations use fire-resistant materials including halogen-free smooth rigid HDPE pipe with 20mm diameter and mounting elements:
- Halogen-free couplings and connectors
- Opening tee
- Metal pipe clamps
- Galvanized brackets
- Anchor nails
- Screws
- Studs
- Anchors
During working documentation stage, manufacturer and support system elements can be replaced with equivalents maintaining cable line fire resistance.
During parallel open laying, distance from low-current wires and cables to power cables should be at least 0.5m, crossing at 90 degrees. Closer placement allowed with electromagnetic interference shielding. Distance reduction to 0.25m permitted for unshielded alarm cables near single lighting wires and control cables.
Cable passages through walls and ceilings consider their fire resistance. Cable routes lay in embedded conduits. Cable passages through walls and ceilings must be sealed with fire-resistant foam. Equipment and cable line marking follows construction standards.
Power Supply
According to reliability requirements, system power consumers belong to category I. For uninterrupted system operation, rack with uninterruptible power supply and external battery blocks is provided, ensuring power for 30 hours standby plus 1 hour voice equipment operation in alarm mode.
For personnel protection against electric shock, protective grounding of all conductive non-current-carrying parts of devices and equipment must be performed. Equipment grounding performed by connecting their enclosures to protective grounding circuit according to electrical codes.
Production Organization Information
Information about production organization and installation work management. Installation of designed system must be performed according to project documentation requirements and technical regulations.
Installation work recommended in following sequence:
- Preparatory work
- Cable pulling and laying
- Device and control unit installation
Preparatory work includes:
- Checking device and cable integrity and functionality
- Material and workplace preparation
Cable condition before laying must be checked by visual inspection.
During work execution, labor safety rules must be strictly observed protecting personnel from electric shock and injuries when working at height.
Installed equipment is not source of harmful emissions. Special environmental protection measures not required. During system operation, no environmental impact occurs as there are no pollutant emissions.
During equipment and cable installation work, provide collection and removal of installation waste according to environmental requirements.
Electroacoustic Sound Calculation
Regulatory sound pressure calculation for speakers in sales areas, public zones, safety corridors.
Initial calculation data:
- Constant background noise level: 65 dBA
- Calculation frequency: 1 kHz
- Horizontal dispersion angle: 120 degrees
- SPL value at 1W power: 94 dB
- Speaker can operate at 6/3/1.5/0.75 W
- Required sound pressure level: 65+15=80 dBA
At 6W power, speaker creates sound pressure: SPL(6W/1m) = 102 dB on radiation axis SPL(6W/1m) = 96 dB at sides of horizontal dispersion angle
SPL reserve on radiation axis: 102-80=22 dB, distance: 13m SPL reserve at dispersion sides: 96-80=16 dB, distance: 6m
Regulatory sound pressure calculation for horn speaker in unloading area and ventilation chamber.
Initial calculation data:
- Constant background noise level: 65 dBA
- Calculation frequency: 1 kHz
- Horizontal dispersion angle: 115 degrees
- SPL value at 1W power: 101 dB
- Speaker can operate at 10/5/2.5/1 W
Required sound pressure level: 65+15=80 dBA
At 10W power, speaker creates sound pressure: SPL(10W/1m)=111 dB on radiation axis SPL(10W/1m)=105 dB at dispersion sides
SPL reserve on radiation axis: 111-80=31 dB, distance: 35m SPL reserve at dispersion sides: 105-80=25 dB, distance: 18m
Escalator Voice Notification System
Equipment complex designed for transmitting escalator safety messages and timely notification signals to prevent accidents and notify people about fire and other emergencies.
The system provides:
- Escalator usage rule messages
- Accident possibility notification
- Fire notification
Terrorist threat notification. Escalator voice notification system is implemented on professional equipment. Notification performed by broadcasting texts about escalator usage rules, evacuation necessity, evacuation routes, movement directions and other safety actions, particularly to prevent panic. Audio notification performed by broadcasting voice messages through speakers installed in escalator areas.
Secondary Power Source Calculation
UPS
For uninterrupted power supply of amplifiers, additional UPS must be provided according to standards requiring at least 30 hours standby plus one hour alarm operation. Each amplifier has charger plus four lead-acid batteries with 65Ah capacity and 12V output voltage.
Equipment justification:
- 1-hour alarm calculation: 9Ah
- 30-hour standby calculation: 45Ah
- Total required: 54Ah (with reserve)
- Equipment comparison: 65Ah > 54Ah - Requirements met
Installation
Battery connection to charger uses series connection with power cable minimum 2.5mm² cross-section.