Gas detector in industrial refrigeration processes and biological degradation processes, including exhaled breath. Depending on the required sensitivity, different types of sensors are used (e.g., flame ionization detector, semiconductor, electrochemical, photonic membranes). Detectors usually operate near the lower exposure limit of 25ppm; however, ammonia detection for industrial safety requires continuous monitoring above the fatal exposure limit of 0.1%. There are several different sensors that can be installed to detect hazardous gases in a residence. Carbon monoxide is a very dangerous, but odorless, colorless gas, making it difficult for humans to detect. Carbon monoxide detectors can be purchased for around US$20–60. Many local
Lawn mower be made. If more, however, the grass will slip through. Reel mowers also have more difficulty mowing over uneven terrain. There are many variants of the cylinder mower. Push mowers have no engine and are usually used on smaller lawn areas where access is a problem, where noise pollution is undesirable and where air pollution is unwanted. As the mower is pushed along, the wheels drive gears which rapidly spin the reel. Typical cutting widths are . Advances in materials and engineering have resulted in these mowers being very light and easy to operate and manoeuvre compared with their predecessors