Mines, pits and related facilities.
My experience with mines is rather negative. It is very difficult to meet mine explosion safety requirements, so I have never been able to place security equipment directly at depth — the cost of the solution was always higher than the customer's desire to observe something at depth.
Even at De Beers, monitoring directly in the mine is considered unprofitable. There is dust, terrible lighting, and generally not very spacious.
Therefore, equipping mines with security equipment is usually limited to protecting ground structures. However, on the surface, many mines are indeed equipped primarily with an access control system. And not at all because they want to protect the mines from strangers. Quite the contrary, they want to protect people. Mines have strict measures for recording everyone going underground. Additional recording through an access control system is not superfluous.
As for open mines (quarries, open pits), the need to protect them arises extremely rarely. Unless gold-bearing or diamond mines, where there may be prospectors willing to dig manually. In terms of protection, open mines are practically no different from any other large-area objects.
Much more interesting are the associated facilities, often located directly next to the mine — processing plants or metallurgical plants. Of course, first of all, diamond enterprises, gold mining or those mining other expensive, rather rare metals — nickel, chromium, etc. require protection. However, to some extent, aluminum or copper enterprises also need to be protected. Firstly, they usually have very expensive equipment such as platinum electrodes. Secondly, in our time, even the simplest, but massive equipment, and especially long and thick copper cables, are subject to careful protection.
So, it is precisely the presence of thick copper cables (or rather, powerful energy consumers) that is the main feature of enrichment and metallurgical facilities. Small (twenty meters high) ore mills, screens, electric furnaces or electrolysis baths — all this equipment not only consumes megawatts of electricity, but also produces serious electromagnetic interference.
In a residential building, a regular elevator can cause considerable trouble when installing video cameras. In the subway, to protect against nearby trains, equipment racks are sometimes covered in permalloy shielding casings. And near ore mills, fiber-optic equipment has to be used to transmit a video signal over 50-100 meters. An analog video signal is very susceptible to interference at a frequency of 50 Hz. This frame rate was chosen for a reason: when the frame rate coincides with the interference frequency, they (the interference) are not so noticeable. On the other hand, because of such a coincidence, the interference cannot be filtered out in principle without damaging the video signal itself (if the interference were ideally sinusoidal, this could still be dreamed of, but for some reason real machines produce interference of exclusively irregular shape).
In addition to the usual security tasks, mining enterprises also have technological television. In this regard, the tasks of monitoring the melt or hot blanks are technically interesting. The brightness of such blanks significantly exceeds the illumination of surrounding objects. And the dynamic range of the CCD matrix of the video camera is small (in reality, in one frame it does not exceed two orders of magnitude, and even with tricks like SuperDynamic or PIXIM it does not reach three orders of magnitude). Thus, by adjusting the diaphragm, the video camera can be configured either to transmit an image of hot metal or to transmit an image of relatively cold equipment. There is no good solution to this problem. Moreover, automatic diaphragm or automatic shutter speed control, as a rule, react very poorly to sudden changes in illumination when a hot blank (or melt) appears in the field of view. I can only recommend installing two different video cameras, with fixed diaphragms (fortunately, the illumination at the rolling mill is usually stable). A video camera with a small aperture will only show the hot metal, while the second one, with a wide-open aperture, will show the equipment itself. If desired, these two images can even be combined on one monitor: on a computer or even in an analog way, if one of the video cameras supports the full (both frame and line) external synchronization mode. Please note that the camera that is configured to display the «cold» equipment operates in a strong overload (overexposure) mode in the hot metal area. It is necessary to use video cameras that are resistant to such overloads. These must be cameras with a large matrix size (half an inch is the minimum), preferably with a special overload limitation mode (or overexposure inversion).
As unique solutions, I will also mention video cameras designed for monitoring the inside of a furnace. For example, for monitoring the melt in a blast furnace. Or video cameras for monitoring the uniformity of fuel oil combustion in the furnace of a thermal power plant. Such technological solutions allow, by optimizing the technological process, to save a couple of percent of fuel, and these 2-3 percent pay for the very expensive special equipment in a week — water-cooled casings with long thin lenses with a remote pupil, made of high-temperature materials. With such lenses, you can look inside the furnace without the risk of accidentally melting the delicate electronics of the video camera.