Introduction
The TinkerESP Fire & Security Calculators suite is a browser-based collection of professional tools designed to support fire alarm and security system engineers during design, commissioning, and maintenance. Each calculator addresses a specific, standards-referenced calculation that would otherwise be performed manually from tables or formulae.
The tools are intended as design aids only — not replacements for full engineering assessment, site surveys, or professional sign-off. All outputs must be verified against the current editions of the applicable British Standards before implementation on any project.
Battery Calculator
Cmin sizing per BS 5839-1 for standby and alarm durations
DIP Switch Calculator
Binary address encoding for Apollo, Hochiki and similar protocols
Sounder Test Tool
In-browser emulation of standard BS 5839 fire alarm tones
Cable Calculator
Voltage drop, resistance, capacitance and inductance for cable runs
Ohm's Law Calculator
Voltage, current, resistance and power relationships
Smoke Detector Calculator
Detector count per BS 5839-6 area and spacing rules
Extinguisher Calculator
Class A extinguisher provision per BS 5306-8
Sounder Coverage Calculator
Sounder count based on SPL, barriers and acoustic absorption
Getting Started
All calculators run entirely within the browser — no installation, login, or persistent internet connection is required once the page has loaded. No data is transmitted to any server.
General Workflow
- Navigate to tinkeresp.net/firetools/ and select the required calculator from the main menu.
- Enter project values into the input fields. Where tooltips are available, hover over a field label for a description of the parameter and its expected units.
- Results update in real time as values are entered — there is no submit button.
- Review any advisory notes or warnings displayed below the result. These flag values that approach or exceed a standard limit.
- Note or screenshot the result for design documentation. Verify independently against the current standard before implementation.
Battery Calculator
Calculates the minimum standby battery capacity (Cmin, in Ampere-hours) required for a fire alarm control panel in accordance with BS 5839-1. The standard requires the system to remain fully operational for 24 hours in standby followed by 30 minutes in full alarm, without mains power.
Inputs
| Parameter | Unit | Description |
|---|---|---|
| Building Occupancy | — | Selects the standby duration. Continuously Manned uses a 24-hour standby period; Not Continuously Manned uses 72 hours, reflecting the likelihood that a mains failure may go unnoticed in an unoccupied building. |
| Standby Current | mA | Total system current in the quiescent (standby) state. Sum the panel, all detectors, all sounder bases, and any ancillary loads from their datasheets before entering this value. |
| Alarm Load Current | mA | Total system current during a full alarm condition. Include the panel, all activated sounders, released door-holders, and output relays. |
Fixed Parameters
The following constants are applied automatically by the calculator and cannot be overridden:
| Parameter | Value | Source |
|---|---|---|
| Alarm Duration | 30 min | BS 5839-1 minimum requirement. |
| Derating Factor | 1.75 | Applied to the alarm period to account for reduced battery capacity under load. |
| Ageing Factor | 1.25 | Applied to the total result to account for battery capacity loss over the service life. |
Calculation
C_min = 1.25 × [ (I_standby × T_standby) + (1.75 × I_alarm × 0.5) ]
Select the next standard battery size at or above the Cmin value. Common sizes: 7 Ah, 12 Ah, 17 Ah, 24 Ah.
Practical Notes
DIP Switch Calculator
Converts between decimal device addresses and the corresponding physical DIP switch ON/OFF pattern. Addressable detectors, call points, and interface modules store their loop address in a bank of miniature DIP switches set in a binary pattern. This tool eliminates manual binary conversion errors during installation and commissioning.
Inputs
| Parameter | Unit | Description |
|---|---|---|
| Manufacturer / Protocol | — | Select the detector protocol — Apollo XP95/Discovery, Hochiki, or Tynetec XT/XT2. This sets the valid address range, switch count, and bit orientation (DOWN=ON for Apollo; UP=ON for Hochiki). |
| Decimal Address | integer | Enter the address from the panel schedule (e.g. 45). The switch pattern is displayed immediately. |
How Binary Addressing Works
Most addressable protocols encode the address as a binary number across six to eight DIP switches. Switch 1 is the least-significant bit (value 1) and each subsequent switch doubles in value (2, 4, 8, 16, 32…). The address is the sum of values for all switches in the ON position.
45 = 32 + 8 + 4 + 1
SW6(32)=ON SW5(16)=OFF SW4(8)=ON SW3(4)=ON SW2(2)=OFF SW1(1)=ON
Sounder Test Tool
A browser-based audio tool that reproduces standard fire alarm tones through the device's speaker or connected audio output. It is particularly suited to testing audio-triggered door retainers — electromagnetic hold-open devices that release when their microphone detects a fire alarm tone — without needing to activate a live alarm.
Available Tones
| Tone | Pattern | Typical Application |
|---|---|---|
| Continuous | Steady, uninterrupted tone | Standard evacuation signal. The most common alarm sound in UK installations. |
| Slow Whoop | Rising sweep, approx. 3.5 s cycle | Evacuation signal; widely used to trigger acoustic door retainers. |
| Fast Whoop | Rapid rising sweep | Alert or investigate stage in phased evacuation systems. |
| Intermittent | 0.5 s on / 0.5 s off | Alert stage or zone-specific signalling schemes. |
| Temporal 3 (T3) | Three pulses then pause, repeating | International standard evacuation signal; mandatory in some occupancy types. |
| Temporal 4 (T4) | Four pulses then pause, repeating | Alert phase in two-stage systems, distinguishable from T3. |
| Single Stroke Bell | Simulated bell tone | Legacy systems and heritage building installations. |
How to Use
- Open the Sounder Test Tool on a device with a speaker, or connect a portable Bluetooth speaker for on-site use.
- Select the tone that matches the alarm signal configured on the installed sounders.
- Press Play. The tone repeats continuously until Stop is pressed.
- Position the speaker near the acoustic door retainer and observe whether the door releases.
- Adjust device volume if the retainer does not trigger — typically a minimum of 65–75 dB(A) is required at the retainer microphone position.
Fire & Security Cable Calculator
Calculates the key electrical characteristics of a cable run for a chosen cable type and installation. Excessive voltage drop can prevent sounders from reaching rated output, cause addressable loop faults, or prevent door-holders from releasing. Excessive capacitance on addressable loops causes communication errors.
Inputs
| Parameter | Unit | Description |
|---|---|---|
| Cable Type | — | Select from the library of common fire, security, data, power, and coaxial cables, grouped by category. Pre-fills the per-metre resistance, capacitance, and inductance values for that cable type. A quick-facts note for the selected cable appears below the results. |
| Run Length | m | One-way run distance from source to the furthest device. The calculator doubles this to give the full loop length for resistance calculations. |
| Source Voltage | V | Voltage at the supply end — typically 24 V DC for fire systems, 12 V for some security circuits. |
| Load Current | A | Current drawn by the devices on this cable run, used to calculate voltage drop. |
Outputs
| Result | Unit | What It Indicates |
|---|---|---|
| Total Resistance | Ω | Combined resistance of the full cable loop (both conductors) at the selected run length. |
| Voltage Drop | V | Voltage lost in the cable at the stated load current. Displayed in red if the drop exceeds 10% of source voltage. |
| Voltage at Device | V | Voltage available at the furthest device after the drop. Must exceed the device's minimum operating voltage. |
| Est. Capacitance | pF | Estimated cable capacitance over the full run. Critical for addressable loop design — excess capacitance causes communication errors. |
| Est. Inductance | µH | Estimated cable inductance — relevant for power distribution circuits and long runs. |
R_total = Ω/m × Length × 2
V_drop = I × R_total
V_device = V_source − V_drop
Ohm's Law Calculator
A general-purpose DC circuit calculator. Enter values for any of the four quantities — Voltage (V), Current (I), Resistance (R), and Power (P) — and the remaining values are calculated automatically.
Quantities
| Quantity | Symbol / Unit | Description |
|---|---|---|
| Voltage | V (Volts) | Potential difference across the component or circuit section. |
| Current | I (A or mA) | Current flowing through the circuit. |
| Resistance | R (Ω or kΩ) | Resistance of the load, cable segment, or component. |
| Power | P (W or mW) | Power consumed or dissipated. |
V = I × R I = V / R R = V / I
P = V × I = I² × R = V² / R
Common Applications in Fire and Security
- Verifying the correct value of an end-of-line (EOL) resistor for a supervision circuit.
- Calculating current drawn by a load at a known supply voltage to check PSU headroom.
- Determining power dissipation in a resistor or cable for thermal rating checks.
- Fault-finding — measuring resistance across an open circuit to estimate fault location from cable resistance per metre.
- Confirming a sounder base or module operates within its rated voltage and current envelope.
Smoke Detector Calculator
Estimates the minimum number of smoke detectors required to cover a given floor area, based on ceiling height and the coverage rules in BS 5839-6 (domestic premises). The standard defines maximum floor area per detector and maximum radial distance limits to ensure adequate detection.
Inputs
| Parameter | Unit | Description |
|---|---|---|
| Floor Area | m² | Total floor area to be covered. For open-plan floors, enter the full area. For irregular shapes or corridors, calculate each zone separately and sum the counts. |
| Ceiling Height | m | Floor-to-ceiling height, or to beam soffit where beams are present. |
| Area Type | — | Standard rooms (bedrooms, offices), Open plan areas (living rooms, open offices), or Circulation areas (hallways, landings). Affects coverage per detector and any spacing notes returned. |
| System Category | — | Optional. LD1 — maximum protection (all rooms); LD2 — extended protection (circulation plus high-risk rooms); LD3 — standard protection (circulation areas only). Selecting a category appends a guidance note to the result but does not alter the detector count calculation. |
Coverage Rules
Maximum floor area per detector: 60 m²
Maximum radial coverage (r): 7.5 m
The calculator returns the minimum detector count based on area. It does not account for room geometry — confirm that the radial distance rule is satisfied at every point in the space, including recesses, alcoves, and rooms with complex shapes.
Fire Extinguisher Calculator
Determines the minimum number and rating of fire extinguishers required for Class A combustible material risks (wood, paper, textiles, etc.) in accordance with BS 5306-8. Class B (flammable liquids), Class C (gases), Class F (cooking oils), and electrical risks require separate assessment and are not covered by this calculator.
Inputs
| Parameter | Unit | Description |
|---|---|---|
| Floor Area | m² | Total usable floor area. Include all occupied rooms. Stairwells, plant rooms, and unoccupied voids are assessed separately. |
| Hazard Level | — | Low — offices and classrooms with minimal combustibles. Moderate — retail and light manufacturing. High — woodworking, chemical storage, or dense combustible loading. |
| Number of Floors | — | Total number of floors in the building. Each floor must independently meet the minimum extinguisher provision requirements. |
Placement Requirements (BS 5306-8)
- No person should need to travel more than 30 m to reach an extinguisher (Low and Moderate hazard).
- Every floor must have at least two extinguishers with a combined minimum rating of 26A.
- Position extinguishers at storey exits, on escape routes, or near the hazard — but not so close that they become inaccessible during a fire.
- Annual inspection and service required per BS 5306-3.
Fire Alarm Sounder Calculator
Estimates the number of sounders required to achieve the minimum sound pressure level (SPL) throughout a protected area. BS 5839-1 specifies that the alarm signal must reach a minimum of 65 dB(A) at every occupied point — or 75 dB(A) where sleeping occupants must be roused. The calculator selects the required SPL automatically based on the chosen application type, then models coverage using the inverse-square law with deductions for barriers and acoustic absorption.
Inputs
| Parameter | Unit | Description |
|---|---|---|
| Floor Area | m² | Area of the zone being analysed for sounder coverage. |
| Sounder Output (at 1m) | dB(A) | Rated sound pressure level at 1 m from the sounder, as stated on the device datasheet. Typical range: 90–105 dB(A). |
| Application Type | — | Sets the minimum required SPL for the zone: Office/Workplace and Retail/Public/Corridors require 65 dB(A); Industrial/High Noise and Residential/Care Home require 75 dB(A). |
| Fire Doors / Barriers | — | Open plan / No significant barriers; Few doors (1–3 per 100 m²); or Many partitions/doors (>3 per 100 m²). Applies SPL attenuation for obstruction between sounder and listener. |
| Room Acoustics | — | Reflective (hard surfaces, tiled, concrete), Moderate (mixed surfaces, typical office), or Absorptive (carpeted, furnished, soft materials). Affects the reverberant field contribution to overall SPL. |
| Ceiling Height | m | Room height — affects the reverberant field contribution to overall SPL. |
Method
SPL(r) = Lw − 20·log₁₀(r) − 11 − Σ(barrier attenuation)
The tool derives the effective coverage radius of a single sounder (the distance at which SPL falls to the required minimum), then divides the zone area by the single-sounder coverage area to give the minimum count. Positions should be arranged on a regular grid to avoid gaps in coverage.
Disclaimer and Important Information
These calculators are provided as guidance tools only and are not guaranteed to be accurate, complete, or suitable for all applications.
- Verify all calculations independently before implementation.
- Consult current legislation, standards, and regulations — including BS 5839, BS 5306, and relevant building regulations.
- Engage qualified fire safety professionals for system design and installation.
- Ensure compliance with all applicable local, national, and international standards.
- Conduct proper risk assessments and site surveys.
- Never rely solely on calculator outputs for critical life-safety systems.
The author accepts no liability for any errors, omissions, or consequences arising from the use of these calculators. Professional judgment and expert consultation should always take precedence over automated calculations. Fire and security systems are life-safety critical. Always prioritise safety and compliance over convenience.