An article in this month’s issue of Develop 3D intrigued me. It features the Davy Safety Lamp and the production of an exact replica for museum display by 3D printing. The article reminded me of the controversy surrounding the impact of the Davy lamp on miners’ safety. Mining is a dangerous business. There is always the possibility of tunnels collapsing but the use of strong props and careful monitoring of vibrations interpreted by miners’ experience goes a long way to mitigating this. The presence of dangerous and invisible gases is much more pernicious. If flammable such as methane they can cause explosions. And some such as carbon dioxide can cause asphyxiation. The lamp was devised to combat these hidden hazards. The way it works is ingenious. A wire mesh screen encloses the wick. This allows air to enter the lamp and for the fuel evaporating from the wick to burn but the holes are too fine to allow a flame to propagate through them and ignite any combustible gases outside the mesh. The lamp also provided a test for the presence of gases. If flammable gas mixtures were present, the flame of the Davy lamp burned higher with a blue tinge. Lamps were equipped with a metal gauge to measure the height of the flame. If the flame burned higher with a blue flame the miners would know that methane was present. Miners could also place the safety lamp close to the ground to detect gases, such as carbon dioxide that are denser than air and so could collect in depressions in the mine; if the mine air was oxygen-poor the lamp flame would be extinguished. The lamp gave an early indication of an unhealthy atmosphere, allowing the miners to get out before they died of asphyxiation. So the Davy lamp must surely have been a boon to miners, not the case unfortunately. Paradoxically, the introduction of the Davy lamp led to an increase in mine accidents, as the lamp encouraged the working of mines and parts of mines that had previously been closed for safety reasons. Men continued to work in conditions which were unsafe due to the presence of methane gas. Although extractor ventilation fans should have been installed to reduce the concentration of methane in the air, such fans were not installed, as the mine owners claimed this was too expensive. One way to interpret this is that the owners valued the lives of miners less than they valued profits. Also the miners had to provide the lamps themselves, not the owners, as traditionally the miners bought their own candles from the company store. Another reason for the increase in accidents was the unreliability of the lamps themselves. The bare gauze was easily damaged, and once just a single wire broke or rusted away, the lamp became unsafe. Even when new and clean, illumination from the safety lamps was very poor, and the problem was not fully resolved until electric lamps became widely available in the late 19th century. A lamp invented with the intention of making mines safer for those who worked in them had the opposite effect; surely a poignant example of unintended consequences? David and Torben would be pleased to hear about other examples of unintended consequences that might be taught in D&T lessons.