It is apparently not safe, among the poor today who have to use it as they have no alternatives, it leads to all sorts of health problems.
It is also a worse polutant than burning wood.
On the reverse side of the environmental equation, raw biomass is known to emit a number of particulates as well as polycyclic aromatic hydrocarbons (PAHs). Burning solid biomass directly contributes to reduction in air quality, often to a greater degree than oil or other hydrocarbons. Burning animal waste creates more dioxin and chlorophenol pollutants than burning wood does. This is particularly harmful when it is burned indoors without venting.
PAHs are well-known carcinogens having the potential to damage DNA and cause birth defects. Dioxins are derivatives of PAHs and are known to be highly toxic to fish and wildlife. A dioxin level as low as 0.5 micrograms/kilogram (about 0.0000005% by mass) are lethal to some species. Chlorophenol is also an aromatic compound. It is commonly used in pesticides, herbicides, and disinfectants. It is one of the primary components of mothballs. Chlorophenol is less toxic than the above compounds, with lethal doses in the range of 600 milligrams/kilogram or about 50% by mass. Long-term exposure to relatively high levels can lead to damage to red blood cells and to the immune system.
The burning of biomass in the developing world for heating and cooking results in high indoor particle concentrations. Long-term exposure to airborne particulate matter (PM) has been associated with increased rates of acute respiratory infections, chronic obstructive lung disease and cancer.
Combustion of dried animal dung as biofuel results in the generation of highly redox active fine particulates
According to health experts, the smoke released in the burning process contains hazardous gases. Studies show that by inhaling these, people suffer from diseases. There are specially made chulhas or stoves for using of dung cakes. Usually these cakes consist of groundnut husk; paddy straw is also used. When the cakes are burnt, dangerous gases are released, which is then inhaled by people. .
The study by Jadavpur University's School of Environmental Studies says the region's groundwater is contaminated with the cancer-causing chemical which gets into paddy through contaminated water. Cattle that feed on contaminated paddy husk and water produce dung that is likely to contain arsenic.
Researchers say while the dung is burnt in kitchen, as much as 25 per cent of the arsenic in fumes could be absorbed by the respiratory tract of people and lead to diseases such as persistent cough and chronic bronchitis. The arsenic particles in the air might also settle on food and water and contaminate it.
Cow dung smoke could cause arsenic poisoning
In 2010 there was an effort to create and distribute better stoves to avoid these problems but while better, it seems that they still had safety problems.
But “clean” is a nebulous term. Of those 28 million cookstoves, only 8.2 million — the ones that run on electricity or burn liquid fuels including liquefied petroleum gas (LPG), ethanol and biogas — meet the health guidelines for indoor emissions set by the WHO. The vast majority of the stoves burn wood, charcoal, animal dung or agricultural waste — and aren’t, therefore, nearly as healthy as promised. Although these cookstoves produce fewer emissions than open fires, burning biomass fuels in them still releases plenty of toxins. “As yet, no biomass stove in the world is clean enough to be truly health protective in household use,” says Kirk Smith, a professor of global environmental health at the University of California at Berkeley and the leading health researcher on cookstoves
These cheap, clean stoves were supposed to save millions of lives. What happened?