Levels of air pollution in parts of northeastern China have hit dangerously high levels, with the concentration of airborne hazardous particles reaching 50 times the recommended safety limit in some places. The worst affected location appears to be Shenyang, capital city of Liaoning Province, which has become engulfed in a cloud of smog, thought to be caused by an increase in coal consumption for heat with winter on the horizon.

Among the variables measured to determine air quality is fine particulate matter (PM 2.5), which refers to the number of particles 2.5 microns or less in width within each cubic meter of air. According to the World Health Organization’s (WHO) air quality guidelines, this should not exceed an average of 25 micrograms over a 24-hour period, although the BBC has reported that levels reached 1,400 micrograms in Shenyang on Sunday.

Though the WHO insists that its guidelines are intended “for worldwide use,” its recommendations are not a legal requirement, and the organization acknowledges that “national standards will vary according to the approach adopted” by each government. However, failing to stick to suggested levels can lead to a number of public health risks. For instance, particles can cause irritation of the eyes, nose and throat, and can also reach the lungs, causing respiratory and cardiovascular complications.

State media in China has criticized the local government, which it accuses of poor standards of organization and communication in its attempts to protect the city’s air from “unreasonable modes of energy consumption.” For instance, emergency measures to tackle the haze – which include government directives for coal consumption to be halted – were not passed down and implemented quickly enough, and there was a delay in warning the public of the situation.

In August of this year, environmental scientists belonging to the group Berkeley Earth released a report in which they revealed that air pollution is responsible for 17 percent of all deaths in China, killing an average of 4,000 people each day. According to the group’s scientific director Richard Muller, breathing the air in Beijing when pollution is at its worst can be the equivalent of smoking a cigarette and a half per hour.