pollution-related deaths. Coal mining is one of the most dangerous professions in the United States, resulting in between 20 and 40 deaths annually, compared to between 10 and 20 for oil and gas extraction. Worker accident risk is also far higher with coal than gas. In the United States, the oil and gas extraction industry is associated with one to two injuries per 100 workers each year. Coal mining, on the other hand, contributes to four injuries per 100 workers each year. Coal mines collapse, and can take down roads, water and gas lines, buildings and many lives with them. Average damages from coal pollutants are two orders of magnitude larger than damages from natural gas. SO2, NOx, and particulate matter from coal plants create annual damages of $156 million per plant compared to $1.5 million per gas plant. Coal-fired power plants in the United States emit 17–40 times more SOx emissions per MWh than natural gas, and 1–17 times as much NOx per MWh. Lifecycle CO2 emissions from coal plants are 1.8-2.3 times greater (per KWh) than natural gas emissions. The air quality advantages of natural gas over coal have been borne out in Pennsylvania, according to studies by the RAND Corporation and the Pennsylvania Department of Environmental Protection. The shale boom in Pennsylvania has led to dramatically lower emissions of sulfur dioxide, fine particulates, and volatile organic compounds (VOCs). Physicist Richard A. Muller has said that the public health benefits from shale gas, by displacing harmful air pollution from coal, far outweigh its environmental costs. In a 2013 report for the Centre for Policy Studies, Muller wrote that air pollution, mostly from coal burning, kills over three million people each year, primarily in the developing world. The report states that "Environmentalists who oppose the development of shale gas and fracking are making a tragic mistake." In China, shale gas development is seen as a way to shift away from coal and decrease serious air pollution problems created by burning coal. Social impacts Shale gas development leads to a series of tiered socio-economic effects during boom conditions. These include both positive and negative aspects. Along with other forms of unconventional energy, shale oil and gas extraction has three direct initial aspects: increased labour demand (employment); income generation (higher wages); and disturbance to land and/or other economic activity, potentially resulting in compensation. Following these primary direct effects, the following secondary