ARMAC Fire Defence System - Technical Notes Part A

Attach:armaca_image1.png ΔAn adjustable remotely monitored and controlled fire-defence system http://www.armac.au/

- home designed and installed, remotely controlled, based on standoff impact sprinklers and multiple (manual remote and automatic autonomous) layers of control.

Jim Falk

14 January 2026

Table of Contents

  1. Preface
  2. Disclaimer
  3. TECHNICAL NOTES: ARMAC Fire Defence System
    1. Description
    2. Development Stages
    3. Fire threat and critical defence decisions
    4. Sprinkler Layout Around House
    5. Sprinkler System Overview
    6. Adjustable Sprinkler mounting
    7. Five Modes of Sprinkler Action
    8. Pipe connection method
    9. Plumbing in the pump shed
    10. Pump system layout
    11. Placing of tank on crush rock bed
    12. Pump connections to tank
    13. Layout of plumbing in Pump Shed
    14. Outline of the water control system
    15. Pipe Supports
    16. Feeder pipe
    17. Pump
    18. Pump Shed
    19. Pump shed protection
    20. Pump shed ventilation
    21. Consideration of further insulation
    22. Water system components
    23. Tank
    24. Flow, pressure and sprinkler requirements
    25. Intermittent spray Mode
    26. Extending run-time in intermittent spray Mode
    27. Table: Summary of intermittent spray mode
    28. Copper Pipe Risers to Sprinklers
    29. Anti-Syphon Control
    30. Electronics
    31. Introduction to the electronic sub-systems
    32. House electronic sub-system
    33. Fritzbox router, and mesh repeaters
    34. RUT240 Wireless fail back router
    35. Victron Blue Smart IP65 10 amp Charger
    36. The Remote Control Module
    37. Pump-shed electronic sub-system
    38. The Relay Module
    39. The Autonomous Module
    40. Inter-Module Communication
    41. Criteria for Automatic actions in the Autonomous mode
    42. Sensor Failure Fallback
    43. System Testing: The TestSys Module
    44. Voltage surge circuit protection
    45. Parallel circuit protection
    46. LCD DISPLAY in shed of key parameters
    47. Protection against voltage surge and spikes
    48. Protection of electronic components from water spray
    49. Pump Control Module setup
    50. Electronically controlled Valves
    51. Sensors
    52. Motorised 3-way and 2-way valves
    53. Switching the Valves using a single Songe 2-way relay
    54. Programming the microcomputers
    55. Bench Testing the Programmes

Preface

This is what appears to be a comparatively novel DIY fire defence system designed for, and implemented at our house in Fairhaven, Victoria, Australia. Novel elements include the use of stand-off impulse sprinklers to spray across surfaces with water, and a multi-option remote control system operated through a phone/ipad/computer dashboard, supported by multiple redundancy in the event of component failure. That is backed by an autonomous sensor-guided control system which takes over if communication is lost, and compensates if sensors themselves are lost.

It has proved to be an 18 month task (part-time) to design, procure parts, test concepts, and construct the system. This (including all plumbing and electronics) has mostly been done with my own labour. Whilst undoubtedly idiosyncratic it might be some use in sparking new ideas and if any of the approaches were to be attempted again a great deal of research, experimentation and programming might well be avoided. That is the reason for my making available this outline of the approaches implemented.

Clearly this should be treated as one of many possible DIY prototypes and it remains to be, and hopefully will not be, tested in the face of a fire. If any of the ideas were to be commercially adopted they would need rigorous testing against labour and materials costs, effectiveness in multiple conditions, and potential user experience.

Inevitably the final setup has evolved with many small improvements and adjustments since the original plan was conceived. During implementation of the design many additional decisions had to be made, tests of assumptions checked, and new insights incorporated. The outcome is described here in two forms. First there is a user guide, and then Technical Notes giving much more of the detail.

Jim Falk,

January 2026

Disclaimer

Relevant information in this document is made available under the terms of a GNU General Public Licence, version 3 (GPL-3.0) and otherwise with copyright reserved. It is provided for its possible interest value without any warranty whatsoever actual or implied as to its useability. The latest version and coding details will be made available on a similar basis at http://armac.au/.

This content is not offered on a commercial basis, and whilst involving systematic investigation has never been tested in a fire, and hopefully never will be. As with this one, any fire defence system should be designed with the particular goals and circumstances of the owners of the house to be defended, and taking full account of the unique characteristics and vulnerabilities of the site.

In summary, in considering the obligations of the author to you, the answer given to the following short quiz should be taken as your guide:

Suppose you try to follow any or all of the methods described in this document, or any provided software, and your house spontaneously combusts and all that is left is a small patch of yellow ash. Do you get:

  1. A heartfelt apology;
  2. Squillions of dollars in compensation; or
  3. Nothing?

3) is the correct answer.

TECHNICAL NOTES: ARMAC Fire Defence System

What follows is a more technical summary of the system as it is currently set up. It follows in more summary form actual planning documents which were used to design and implement the system as it evolved to its more final form. Some of the planning considerations have been included in order to assist someone wishing to build to their own situation but utilise some of the ideas here.

Description

The house and shed are defended against fire and ember attack with a set of impact sprinklers situated around it in order to provide a wet corridor to the house and to wet all vertical surfaces and decks.1

A DN50 (2" internal diameter) high pressure feeder polypipe (external diameter 63mm) has been laid around the house at a depth exceeding 10 cm (ie a trench depth > 100+50 = 150 mm) which has been shown to be sufficient except in areas where a major fuel load (for example -- running under a burning fence or vehicle).2 Dug by a trenching tool, the trench is generally 250-350 mm in depth. In places where that is reduced earth is back-filled on top. Sprinkler heads are serviced by copper risers each equipped with a brass ball valve, running underground to saddle couplings at the feeder polypipe.

The feeder pipe is connected to a colorbond/aquaplate tank via a diesel pump. The tank sits on a horizontal bed of crushed dust situated behind the brush fence on the side deck. A 30,300 l (3.5m diam, 3.1 m high) tank is fed from the water mains regulated with a float valve to ensure it replenishes utilised water. A recirculation circuit allows water to be directed at will from the pump back to an inlet at the top of the tank.

The pump is housed in a metal weatherproof shed, mounted on a concrete pad and protected by water sprays. It is able to be started both manually, by various remotely controlled switches which can turn it on and off, and/by an autonomous module programmed to respond to various sensors, including to temperatures measured inside and outside the shed.

Video and tank water-level monitoring are incorporated, integrated to the home internet via wifi. The control of the system is via an LTE G4 SIM card (for the pump) and, for the other components, via home WiFi so arranged that if connection is lost the connection will failover to another LTE G4 SIM card. The home Fritzbox is powered by a 22AH 12V lead acid battery run through a mains connected inverter, battery charger and surge protection unit.

The system has been compared with local commercially available roof-mounted fixed spray systems and although different in concept appears to offer similar or better protection together with adjustable rates of water usage, more targeted wetting of potentially vulnerable surfaces, and the capacity for many hours more of intermittent cinder defence. (For some further discussion of this see Appendix 7) The current arrangement of impact sprinklers is shown on the next page. The current system was installed (albeit mostly by means of the owner/designer's labour) for $31,000.

Of that cost, roughly one third was for some paid assistance to trench and bury the feeder pipe, emplace the posts, construct the shed concrete pad and tank base), one third for basic infrastructure (shed, tank, pump, and pump control module), and the remainder for copper pipes, hoses, brass and stainless steel fittings, sprinkler heads, control valves, sensors, and some needed plumbing and electronics tools, and electronic components.

Development Stages

This system has gone through a series of design stages. Two things have happened in this process.

First the system has become more sophisticated to deal with both encountered challenges (such as voltage spikes when the pump is cranked) and further stages of protection (for example giving the system autonomous capabilities if manual control is impossible for example due to loss of communication with the external world).

Second, consequent design development has allowed the implementation of much more efficient, robust, and in some cases considerably simplified design. Of the latter, the most evident example has been in the arrangement of communication between electronic modules.

Originally command of the system was to be applied from a module in the house, connected to the internet on the one side, and via relays in the pump shed to the sensors and valves of the sprinkler system. This required a 13 core cable to be laid between the house and the pump shed and two micro computers (Arduinos) in the house to operate relays and analyse sensors inputs over the 10 meter 13 core cable. In the end however, this proved insufficiently robust.

In the current arrangement the house electronics simply sends commands and receives information from the modules in the pump shed. The pump shed modules deal with operating the valves, receiving and analysing sensor data, and also making all pre-programmed decisions based on this data, and then directly commanding the relays. This information transfer requires only two ("A and B") wires, operating a little like a telephone with RS485 transceivers at each end. This communication system is much more robust and also flexible, since capability is not limited by the number of available wires. In the shed one microcomputer analyses sensor data, whilst the other makes the autonomous decisions when required, and commands the relays. This also allowed major simplification of one of the microcomputer programs, dropping it from around 3,500 lines of code to 1,300 lines.

These notes describe the system in its current development stage. However, where appropriate some note is made of earlier considerations and decisions how those have now been modified.

Fire threat and critical defence decisions

Early warning is an important component of defence against fire. Decisions must be made about when to set the system on, and off, and need to take into account the minimum requirements of the system to operate, different modes of applying cooling, and available water in the face of the combustion threat posed by the approaching fire.

In the past the advice had been that if an owner was prepared and equipped to defend a property against fire, then they should stay and defend. If they were not they should leave early. However, following a series of major fires that advice has changed and hence two capacities are needed:

  1. A remote control system able to be used anywhere where internet/mobile network capabilities are available.
  2. An autonomous control system able to run the system according to a pre-determined decision matrix, if remote communication with the system becomes unavailable.

Both of the above require an adequate and practical set of sensors which can inform decision making whether remotely or on-site.

Primary awareness of vulnerability to a fire is provided by emergency warning from fire authorities and in particular warning in real-time of significant fires which pose an on-going threat. That is available from the VicEmergency App, and its warnings are built into the system control panel.

The next threat is the approach of wind bearing embers -- sometimes called firebrand attack.3 Flame detectors are available, but the range tends to be limited and resolution either too good or not good enough. The crucial question is whether there is an incoming wind carrying embers of sufficient thermal output to pose a threat to wooden structures or ignite grass or other flamable materials which can create such a threat. The system here is designed to greatly reduce the impact of such an attack, but can only do so if ember attack at dangerous levels has commenced.

In this system the approach taken has been twofold:

  1. to create some direct measurements of threat by setting up "ember traps" filled with flamable material, but sheltered from rain, and equipped with simple thermal sensors which will report when either radiation from a glowing ember is detected, or the flamable "bed" within the trap is set alight. The choice of flamable material in this system is cloth soaked in hardened paraffin wax which is resilient not only to the elements in normal days (eg rain) but also to the early temperature rise in an on-coming fire, but highly flamable. These are maintained in an open but roofed metal box (the normal metal chimney cowls which are cheaply available). The wires are above ground, since once a trap has detected on-coming embers it and its connected wires has served its purpose. The relevant detection signals are available both to the autonomous module of the defence system, and on the remote control panel.
  2. To create a single infrared flame sensor in the 720 nm frequency range, which although only short range (1 m) can detect with considerable sensitivity small burning embers, supplemented by detection of small particles.

A video camera is also helpful for as long as it lasts, to survey the area of fire approach. Most of these operate in both the visual and infrared frequencies and a moveable camera is provided with its input able to be viewed in the remote control panel.

Later, as the fire front itself arrives, this is determined by both the external temperature, and the external temperature rise, since in bushfires, the temperature rises very rapidly in the later stages of the fire-front's approach.

Sprinkler Layout Around House

Attach:armaca_image2.png Δ

Attach:armaca_image3.jpg Δ

Sprinkler System Overview

Three sprinkler heads were chosen.

  • Red (1, 7, 9) are VYR60 -- dual nozzle sprinklers (3.6 mm, 2.4 mm) and are fed by 20mm copper pipe from the feeder pipe. Their published characteristics are for different pressures: 180 kPa radius 16.3 15.3 lpm; for 420 kPa radius 24.6 24 lpm
  • Blue (2a, 2b, 3, 4, 5, 6, 10) are Pope Heavy Duty sprinkler heads which are fed by 15mm copper pipes. Their published characteristics are 10LPM at 100kPA, 18.9LPM at 350kPA; and in each case a 12.5 m max radius.
  • Shed cooling sprinkler heads whilst not explicitly shown are 12mm fan sprays fed by 12mm copper pipe with 5 angled to cool the pump shed roof and walls.

The siting of sprinklers was determined by pre-planning considering their rated spray radii, followed by testing. To do this at each position a corresponding sprinkler was placed on a flexible moveable pole, and was fed by a rubber hose with tap water further pressurised with a small electric centrifugal pump. The positions were then experimented with at different heights, angles and positions to achieve optimum overall coverage.

This at least gave initial confidence as to the likely capabilities of the sprinklers, their minimum area of wetting, and the heights and positions to place them. However, later even after the feeder pipe and pump were operational and the poles established, the sprinklers were still initially connected by rubber hose so that their heights could be adjusted, and only when that was finalised were they plumbed in with copper pipe.

  1. This VYR60 dual nozzle has the double job of wetting the side as well as deck front of the house. It is positioned at the steps on the W side of the house. Height of bottom of sprinkler to ground is 2 metre.

Attach:armaca_image4.png Δ

  1. If we had used a VYR60 here it would need to be to be 3.6 m above ground and the far bedroom wall would still require supplementary spray. So the single VYR60 was replaced with two Pope sprinklers which do an excellent job at their minimum operating pressure of 36 PSI covering from the end bedroom to the middle living room window.

2a is positioned on third of the way from the middle of the two living room windows, on the boundary and at a height of 2.2 metres

2b is positioned two thirds of the way, on the boundary at a height of 2.2 metres.

Attach:armaca_image5.png Δ

  1. Pope at a height of 500 mm, produces a small segment of spray to protect end of house

Attach:armaca_image6.png Δ

  1. Pope at height of 150 mm to keep side of house wetted including windows. Tree in corner nearest house (end of dog run) to be removed both to reduce fire risk and remove wetting obstruction.
  2. Pope at height of 100mm keeping shed, gas bottles, and north facing door, deck and walls wetted.

Attach:armaca_image7.png Δ Attach:armaca_image8.png Δ

  1. Pope at height of 100mm to keep north wall of shed wet. It is intended to supplement this with another 12 mm fan spray to wet up to roof peak (adding to water consumption by 0.5 l/min -- 1/l/min on low and high pressure modes respectively).
  2. VYR60 mounted over house roof (over end of barrel roof) sprinkler runs 360 deg wetting not only the roof and gutters but also surrounds. It is attached to the wall below the roof and penetrates the external barrel roof and is sealed with copious amounts of silicon sealant.

Attach:armaca_image9.png Δ

  1. Pope attached to vacuum breaker post (see later) wets the clerestory windows above the W side verandah roof.
  2. VYR60 at N brush fence entrance to house at a height of 1.2 metre. Job is keeping West and South of shed, North facing door, deck and walls wetted (overlapping 5) and east deck (overlapping 1) wetted.
  3. Pope at height of 2 meter was added after the main system was already put in place since it was seen that additional wetting was required for the clerestory windows and roof above the back (guest) section of the house. One sprinkler was seen to be able to do the job well adding only a further 10 L/min of water draw.

Attach:armaca_image10.jpg Δ

Adjustable Sprinkler mounting

The sprinklers mounts are designed to enable their angle of spray to be adjusted vertically and horizontally. The precise segment of spray can be adjusted at the sprinkler based on the geometry of the area of application. The initially chosen configuration of sprinklers after experimentation is shown below.

Attach:armaca_image11.png Δ

Five Modes of Sprinkler Action

The system operates in five modes (controlled by four motorised valves, and one solenoid valve).

  1. Shed cooling only.
  2. High Volume: to run for up to 30 mins when the fire front is close to arriving or has arrived (say when temperature sensor indicates > 65 deg C)
  3. Low Volume: for cinder attack prevention, capable of running for at least 3 hours.
  4. Intermittent low volume: spray mode by means of a 3-way motorised valve switching between flow and recirculation to the tank, or, when battery voltage > 12.25 V and cycle length ≥ 5 min, by starting and stopping the pump.
  5. Low Volume -- gel injection: capable on command or near exhaustion of water to apply a coating of Barricade gel to the house.

A pressure gauge and flow meter4 allow manual observation of the flow characteristics, and an online flow sensor provides important information when the system is in operation under remote control.

The 30.3 k litre tank is fed from house main controlled by a float valve. A ¾" Floating Ball Automatic stainless steel valve ($10.17 on Aliexpress) was used for automatic refill, given the max working pressure is 1MPa which is greater than residential tap pressure (0.3-0.5 MPa).5

Whilst in order to keep options open, the tank was ordered with a 65mm outlet in the end it was decided that the DN50 outlet to DN50 pipes would be sufficient. A suitable silicon wire reinforced inlet hose with appropriately sized inlet and outlet sleeves was available on Aliexpress.

Pipe connection method

There are of course various choices for connecting up a plumbing system. Obvious choices are brazing, press fittings, brass compression fittings using copper olive inserts, or the more old fashioned brass flared compression fittings.

The cheapest approach is to use flared copper compression fittings, and these can often serve in place of barrel unions to allow pipe sections to be removed for maintenance.

It is possible to use Kempress press fittings from Plumbingsales.com.au and cheaper than the B-Press fittings available from Reece (even at trade rates). Appropriate press tools such as the Rothenberger 4000 B-Press Tool kit can be hired from Reece (Torquay) for $100 a day, or an equivalent from Kennards (Geelong) for a little less. The Kempress fittings are universally able to be fixed with any of the major available press tools. They are however more vulnerable to heat because of their inner silicon sealing olive. Fire rated fittings are available but at an considerably more elevated price.

Ultimately, for reasons of availability, flame resilience, and cost (but not necessarily ease of construction), flared fittings were used in most situations, with an occasional use of a copper olive insert compression fitting where it was cost effective and appropriate. Where DN50 copper pipe was utilised, the ends were annealed using a MAP gas torch prior to flaring with a flaring block and pin.

Plumbing in the pump shed

The pump shed provides shelter for the pump, its electronics and its pipes. A shed cooling system is designed to keep the temperature inside the shed at tolerable levels.

A decision was required as to whether to stick to brass and copper plumbing in the pump shed or to utilise cheaper PVC piping throughout. The maximum temperature for PVC pipes is cited as 50 deg C at which temperature the design pressure rating drops from 2 to 0.46 The maximum temperature for auto wiring is 120 deg C with self ignition temperature of Dieseoline at 210 deg C so these are not immediate issues. The maximum operating temperature of Garpen pump is not yet clear, but 120 deg F = 49 deg C is cited in the US standard7 which is also cited as the max temperature for a fire room, and also the maximum ambient temperature for Bianco Pumps. However, practical experience of those in the field suggests the Garpen pump can continue to operate at much higher temperatures. Perhaps the most vulnerable component is the Dosatron with a rated maximum operating temperature of 40 deg C. For this reason it is to be clad with insulating lagging and provided with a fail safe arrangement so that it is monitored, and will be isolated if failure is detected.

Based on the above, even though we are relying on the shed sprinkler to keep temperatures within workable range it was decided to continue with brass fittings and copper piping, and fire rated hose, wherever available.

Pump system layout

Attach:armaca_image13.png Δ

Placing of tank on crush rock bed (view towards house)

Attach:armaca_image14.png Δ

Pump connections to tank

The pump comes with 3" outlets and corresponding hose tails. On the basis of performance curves for the pump (see later) the inlet and outlet was ultimately reduced to 2" utilising brass/stainless steel reducers.

Planned:

Attach:armaca_image15.jpg Δ

Footnotes

1 As Dr Leonard from CSIRO says: "I find that the perimeter sprinklers, ones out in the broader area of the garden projecting back towards the house, are potentially far more effective [than roof mounted sprinklers] because they get it under the eves, they get it on the wall surfaces, and they deliver water to all those ground and surface fuels. I've never seen a spray [ie fixed spray] system design that's particularly effective at solving all aspects of bushfire risk that an otherwise vulnerable house could face." https://bushfireresilience.org.au/topics/sprinkler-systems/

2 See https://bushfireresilience.org.au/wp-content/uploads/2022/03/Video-07-Sprays-2.pdf Justin Leonard "Minimum 100mm" ... unless a vehicle or pile of wood or a fence is burning above the line, in which case needs to be deeper.

3 Jeffrey D. Kepert, "Ember transport for bushfire simulation, Natural Hazards Research in Australia, Report No. 12.2023, Australian Bureau of Meteorology, 2023, https://naturalhazards.com.au/sites/default/files/2023-02/Ember%20transport%20for%20bushfire%20simulation_12.2023.pdf

4 Example: https://www.aliexpress.com/item/1005005638559437.html

5 https://www.aliexpress.com/item/1005005482258775.html

6 https://www.vinidex.com.au/technical-resources/pvc-pressure-pipe/pvc-temperature-considerations/

7 https://higherlogicdownload.s3.amazonaws.com/SFPE/93e7d31c-6432-4991-b440-97a413556197/UploadedImages/FPE_Extra/Issue_83/22_November_FPE_Extra2.pdf

Continue to: Part B | Part C

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Page last modified on February 09, 2026, at 12:38 pm