Every time he enters an industrial warehouse engulfed in flames, a firefighter puts his life at risk. The smoke is extremely toxic and visibility is very low. He has around 20 minutes of oxygen stored in his tank and typically, given the obstacles, can only advance 12 metres a minute. That equates to a maximum range of 120 metres whereas, on average, a modern day warehouse is some 400 x 200m2. Fire crews from the South Yorkshire Fire and Rescue in the UK told researchers that industrial warehouses are a particular concern. The combination of a large surface space and smoke makes it notoriously difficult and sometimes even deadly to navigate. Numerous firefighters have lost their lives in warehouse fires. The near total black out caused from smoke easily disorients them. They risk getting lost. Taking its cue from there, the EU- funded Guardians ('Group of unmanned assistant robots deployed in aggregative navigation supported by scent detection') project constructed a swarm of autonomous robots specially designed to assist firefighters searching large warehouses. Swarming, in robotic terms, is based on pioneering research that simulates a flock of birds in flight. The project built on this concept so that their autonomous robots are able to move in a manner that is influenced by geometric distribution. 'As far as I know, we are one of the first who are trying swarm robotics in a real environment,' says Jacques Penders, Guardians' project coordinator. 'The focus is to get the robots to cooperate with one another and be able to operate in both small and large groups.' For firefighters, every second and every minute count. In Worcester, USA, six firefighters lost their lives when they became lost in a six-storey warehouse. Concrete walls, reinforcements and metal racks interrupted vital communication lines. Similar tragic incidences have also occurred in Europe. The swarm of robots developed by Guardians, therefore, needs to provide viable guidance information between themselves, and rescuers under extreme conditions. This required the researchers to design and experiment with interfaces that present only the most essential information to guide the firefighter. And in conditions that exposed robots could withstand. A firefighter will first move along the edge of a wall when he enters a warehouse. The wall is his point of reference. Only on very rare occasions will fire crews advance into a void because the smoke becomes progressively thicker. 'The smoke concentration increases the further away one moves from the walls,' according to project literature. Most robotic sensors, like cameras or laser range finders (LRF), do not always optimally perform under stressful conditions. Warehouses can contain metal racks with shelves that may also store metal-based packaging such as tins or buckets. This intricate metal landscape interferes with the transmission and reception of radio signals. Additionally, particles in the smoke deflect lasers. 'Firefighters usually have a map of a building they are about to enter. As they enter the building they count their steps to keep their bearings and locate themselves. The robots basically do the same thing,' says Mr Penders. The first robot positions itself at the entrance and establishes a beacon. It remains there throughout the search. The second robot moves along the wall, and then a third. The third robot becomes the third vertex of an equilateral triangle. More robots then advance and use a triangle of nodes and communication lines between relay nodes. The robots are able to communicate with one another through a wireless communication network. 'Smoke interferes with the conventionally used, light-based sensors,' notes Mr Penders. 'This is why we are looking at using microwave,' he adds. As the robots venture further into the building, they develop a grid that becomes a 2D metric map and they use networking behaviour to maintain and expand communications. However, if a robot becomes detached and loses the swarm's signal, it will either return to a 'predefined site, return to the last known position where the wireless signal was strong enough or be opportunistic and search forward assuming some fellow swarm members will soon be found,' according to the Guardians project. Project researchers also want the robots to actively support the firefighter during a rescue operation. The swarm must be able to interact directly and coherently with the rescuer and determine the direction he should follow. At the most basic level, the swarm will react autonomously to the movement of a firefighter. When he moves, the swarm will as well. Because firefighters are already under considerable mental and physical stress, the swarm must not present an additional burden or unnecessarily distract his attention. Instead, the swarm must complement the search and rescue mission. Researchers, therefore, had to ensure the robots express appropriate and consistent behaviour, as well as interfaces that allow firefighters to keep their bearings. Most robot-assisted search and rescues are operated by a human outside the danger zone. The Guardians project is unique because a human being is able to cooperate with several robots in the field. But this requires innovative interfaces which enable the firefighters to interact with the swarm with no additional effort. Also, given the harsh conditions, firefighters cannot rely solely on eyesight and hearing or even commonly used audio-visual technology. To overcome these challenges, researchers designed a feedback interface ― a visual device that is then installed inside the firefighter 's helmet. Researchers are also developing a tactile interface that can be installed on the firefighter 's body. Guardians designed and built two light array visors. Each visor was tested by the South Yorkshire Fire and Rescue and enabled researchers to adjust settings to increase performance. However, this meant multiple tests through trial and error as firefighters expressed some initial ambivalence with the devices. 'Swarm robotics in combination with a human being was both interesting and challenging. The long-term aim though is to earn the confidence of the human being because the signals can sometimes distract,' says Mr Penders. 'We need to look at how the firefighters can use this system.' First of all, the interface needs to provide a visual feedback of the swarm's streaming data. This is done by displaying an array of RGB LEDs on the inside of the visor. At the same time, the firefighter needs to have complete confidence that the information is correct. Understandably, few firefighters will venture or stray from a wall or other landmark because of the inherit dangers involved. The first visor tested indicated both the safest and best direction to take. During the test, firefighters were asked to undergo regular search and rescue activity. They were also required to perform several additional tasks including verbally reporting to the coordinating researcher about their progress and to their fellow participating colleagues. Results indicated that the firefighters sometimes ignored the RGB LED direction signal. The firefighters informed the researchers that the direction data displayed inside the visor needs to be more simple and unambiguous. The second visor was mounted on a fully operational fire fighting helmet. Alongside the LED display, researchers placed an internal measurement unit (IMU) sensor that detects the firefighter 's orientation while following commands. As in the first test, the firefighters were asked to perform a number of activities. But unlike the previous trial, where direction information was constantly updated, the second trials provided the firefighters with fewer commands. The outside of the visors were covered so that the lead firefighter had to rely on the visor's signals for navigational commands. A second firefighter, also blind folded, then followed the lead firefighter as is standard practice under normal search and rescue protocols. Both were tethered to a rope. The firefighters were asked to count the number of times two different coloured lights flashed inside the visors. The flashing lights were added to create additional stress. The firefighters were still able to follow the commands of the lead firefighter. The project has laid the foundation of promising research that combines cutting-edge technology with pioneering swarm techniques. The robots designed by Guardians can also warn the firefighters of any toxic chemicals in the air. As well, these new systems could be used in other disaster scenarios. The algorithms developed by Guardians mean the robots can follow a firefighter without communication. It is this autonomous feature, along with their ability to transfer information to the firefighter in specially designed visors, which makes the Guardians project stand out. 'We did a final demonstration at the South Yorkshire Fire and Rescue,' says Mr Penders. 'And they confirmed that the use of robots could help especially in high-risk situations.' Guardians project received funding under the 'Information and communication technologies' theme of the EU's Sixth Framework Programme.