The client is a supplier of safety monitoring systems into healthcare, education and other public buildings. Their systems currently monitor the active parts of fire safety systems such as alarm buttons and fire and smoke detectors. The more passive parts of fire safety systems, such as equipment to tackle small fires, are currently monitored via manual inspections and our client saw an opportunity to enhance their current systems by automating the monitoring of passive items such as extinguishers and fire doors.
In our initial meetings, the client identified a base feature set and an extended feature set for monitoring doors and extinguishers. At the most basic level doors need to be monitored to ensure they are closed to stop the spread of fire, and extinguishers need to be monitored to ensure they are present at all times in the correct locations. The enhanced features include being able to determine if an extinguisher is full charged (with water, foam or carbon dioxide gas) and ready for use and also if anything has been placed in front of an extinguisher to obstructing its visibility. To make the installation of the monitoring units easy they needed to be battery powered with minimum 1 year battery life and use a wireless method to communicate to the backend monitoring software. Update frequency of the door state and extinguisher presence can be low as the typical expectation is that these items will remain in their default state nearly all the time. To ensure a resilient system the monitor units need to alert the backend management software in case of low battery level and the backend software needs to know if a monitor unit is lost from the wireless communication network for an extended period of time.
Meeting the basic requirements of monitoring door state and extinguisher presence needed a simple solution based on magnetically operated switches such as you find in most security systems for door state detection. The magnet is attached to the door and the magnetically operated switch is attached to the door frame. For the extinguishers, the magnet is securely attached to the extinguisher and the magnetically operated switch is mounted to either the wall or extinguisher bracket as appropriate to give reliable operation.
Meeting the enhanced requirements could also be achieved using fairly standard sensing techniques. A fully charged extinguisher will have a known weight. The weight of the extinguisher can be measured by a pressure sensor mounted either on the floor (for a floor standing unit) or on a wall bracket. Detecting an object obscuring the visibility of an extinguisher can be achieved using an ultrasonic ranger which will indicate anything in the way up to a range of 3m.
The design work was done to include support for these additional features but in doing so it became clear that, at least initially, the extra cost of these sensors would bring the unit cost to a level where it could be difficult to sell, and identifying a solution to fit the variety of extinguisher brackets could be difficult. So at least for the first stage of the work these enhanced features were put on ice.
The wireless connectivity required some thought. Initially a mesh network appeared a good solution but given the unknown nature of the radio environment in a target building and the unknown distances between monitor units and gateways we could see there may be situations where not all units would be able to join the mesh network successfully. Instead LoRa appeared a more reliable option – although mainly intended for longer range requirements – it’s use internally is fine and allows coverage across even the largest of buildings.
During initial testing it was established that signals from the LoRa devices could be blocked by internal structures i.e. elevator shafts. It was decided to document a process for the client to enable them to do a survey of a building where an installation was being planned. This would enable them to check propagation of the LoRa signal around the building specifically looking at communication between the furthest ends of the building and between floors. The results of the survey then guides the specification of the number of gateways required and their best location.
The battery requirement is aided by the low update rate requirement, so for most of the time a unit can be in a very low power state just making a reading of its magnetic switch sensor once an hour and reporting this back to the gateway.
The client’s existing back end monitoring and management software needed to be interfaced to this new monitor network. We provided a simple API for the client to invoke from the existing system.
We spent the first part of the project on detailed design and specification work to address the client’s requirements, the known challenges and also to identify other points requiring client input or decision making. The result of this being a final specification for the monitoring unit, the gateway unit and the API to interface with their management software. Once the client signed off on this specification the work moved into the building of prototypes, both hardware and software to prove out the solution concept.
Primary benefit of this solution is to replace a manual inspection process to ensure that fire doors are closed and extinguishers are present. This automated solution enables the freeing up of resource to focus on more valuable activities while ensuring that in the unlikely event of a real fire situation doors are closed to contain the fire and extinguishers are available to tackle minor situations.
The monitor units are easy to install as they are battery powered and use wireless communication, so only a short run of wiring is needed to connect the magnetic switch to the monitor unit in the most secure way.
The client can continue to use their well known management solution as they have a simple API reporting back to them the confirmed presence of all monitor units on the network, the battery status on each unit and the status of the magnetic switches detecting the door or extinguisher state.
The client also has an enhanced unit option available should a particular customer find the benefits of improved extinguisher monitoring be required and the unit could be used to monitor presence of any other health and safety relevant statically located item or any other high value item.