Blending conventional High Speed Diesel Fuel (HSD) with Biodiesel (usually methyl esters of vegetable oils) is presently the most common form of use of Biodiesel. The most common ratio is 80% conventional High Speed Diesel fuel and 20% vegetable oil ester, also termed B20, indicating the 20% level of Biodiesel. There have been numerous reports that significant emission reductions are achieved with these blends.

No engine problems are reported in large scale tests with, for example, in urban bus fleets running on B20. Fuel economy was comparable to HSD, with the consumption of Biodiesel blend being only 2 to 5% higher than that of conventional HSD. Another advantage of Biodiesel blends is the simplicity of fuel preparation, which only requires mixing of the components. Ester blends have been reported to be stable. A blend of 20% oil or Biodiesel with 80% HSD did not separate at room temperature over a period of 3 months. A 50:50 blend of oil with HSD was also found quite stable. Several studies have shown that Diesel / Biodiesel blends reduce smoke opacity, particulate matter, un-burnt hydrocarbons, carbon dioxide and carbon monoxide emissions. Nitrous monoxide emissions are slightly increased. One limitation to the use of Biodiesel is its tendency to crystallize at temperatures below 0°C. Methyl and ethyl esters of vegetable oils will crystallize and separate from diesel at temperatures often experienced in winter. Such crystals can plug fuel lines and filters, causing problems in pumping of fuel and engine operation. One solution to this problem may be the use of branched-chain esters, such as isopropyl esters. The isopropyl esters of soy bean oil crystallize 7 to 11°C lower than the corresponding methyl esters. Another method to improve the cold flow properties of vegetable oil esters is to remove high melting saturated esters by inducing crystallization with cooling, a process known as winterization.

Pure vegetable oils are completely harmless to the environment, especially the groundwater. However, esterification of vegetable oil increases its water hazard. Some Environment Protection Agencies classify waste vegetable oil as a toxic waste. As a general rule blends of Biodiesel and petroleum diesel should be treated like petroleum diesel. It is recommended to store biodiesel in clean, dry and approved tanks. Though the flash point of biodiesel is high, storage precautions somewhat like that in storing the diesel fuel still need to be taken. Biodiesel can be stored for long periods in closed containers with little head room but the container must be protected from direct sunlight, low temperature and weather. Underground storage is preferred in cold climates but Biodiesel can be stored in open with proper insulation, heating and other equipment should be installed. B20 fuel can be stored in tanks, above ground depending on the pour point and cloud points of the blend. Low temperature can cause Biodiesel to gel. Additives can be used for low temperature storage and pumping. The Biodiesel / its blends should be stored at temperatures at least 15°C higher than the pour point of the fuel. While splash blending of the Biodiesel, care should be taken to avoid very low fuel temperatures, as the saturated compounds can crystallize and separate out to cause plugging of fuel lines and filters. Condensation of water in the tank should be avoided as hydrocarbon degrading bacteria and mould can grow and these use Biodiesel as food.

Biodiesel and its blends are susceptible to growing microbes when water is present in fuel. Biocides, chemicals that kill bacteria and moulds growing in fuel tank, can be added in small concentration. Biocides do not remove sediments. Moreover, storage of Biodiesel in old tanks can release accumulated deposits and slime and can cause very severe filter and pump blockage problem. For long term storage stability of Biodiesel and blends, adequate data are not available. Based on experience so far, it is recommended that Biodiesel can be stored up to a maximum period of 6 months. Some anti-oxidant additives are also used for longer periods of storage. Similar periods are applicable for storage of Biodiesel and its blends in vehicle fuel tank. Since Biodiesel is a mild solvent, Biodiesel has a tendency to dissolve the sediments, normally encountered in old tanks, used for diesel fuel and these cause filter blockage, injector failures in addition to clogging of fuel lines. Brass, copper, zinc etc oxidizes diesel and Biodiesel fuels and create sediments. The fuel and fittings will start changing color as the sediments are formed. Storage tanks made of aluminum, steel etc should be used.

As a general rule blends of Biodiesel and petroleum diesel should be treated like Petroleum Diesel. Biodiesel (vegetable oil methyl esters), contain no volatile organic compounds that can give rise to poisonous or noxious fumes. There are no aromatic hydrocarbon (benzene, toluene, xylene) or chlorinated hydrocarbons. There is no lead or sulfur to react and release any harmful or corrosive gases. However, in case of Biodiesel blends, significant fumes released by benzene and other aromatic chemicals present in the petroleum diesel fuel can continue. On contact with eye, Biodiesel may cause irritation to eye. Safety glasses or face shields should be used to avoid mist or splash on face and eyes. Fire fighting measures to be followed as per its fire hazard classification. Hot fuel may cause burn. Biodiesel should be handled with gloves as Biodiesel may cause soft skin. Mild irritation on skin can occur.

Indian Explosive Regulations classify the product as C Class (Similar to Heavy oils due to its high flash point). The glycerine also falls under same classification. There is no risk of explosions from vapors of Biodiesel as the flash point is high and the vapor pressure is less than 1 mm Hg. Large Biodiesel spills can be harmful. Biodiesel, while not completely harmless to the larvae and fish, is less harmful than petroleum diesel fuel.

Biodiesel (methyl esters), have very low solubility in water (saturation concentration of 7 ppm in sea water and 14 ppm in fresh water at 17°C) compared to petroleum diesel that contain benzene, toluene, xylene and other more water soluble, highly toxic compounds. However, when the Biodiesel is vigorously blended into water, the methyl esters form a temporary emulsion of tiny droplets that appear to be harmful to the swimming larvae. The half life for biodegradation of vegetable methyl ester is about 4 days at 17^oC, about twice fast as petroleum diesel. In the laboratory tests, rape seed methyl ester degraded by 95% while the diesel fuel degraded only 40% at the end of 23 days.

Any accidental discharge / spill of small amounts of Biodiesel should have little impact on the environment compared to petroleum diesel, which contains more toxic and more water-soluble aromatics. Nonetheless, the methyl esters could still cause harm. Environmental Protection Agency still considers spills of vegetable oils and animal fats as harmful to the environment. Spilling Biodiesel in water is as illegal as spilling petroleum. Biodiesel need to be handled like any other petroleum fuels and laws should be reviewed to ensure that Biodiesel is covered in the same class, if not included already. When biocides are used in the fuel tank to kill bacteria, suitable handling precautions like use of gloves and eye protection is must. One must check if the laws on disposal of petroleum products are applicable to Biodiesel also. Similarly check if laws for spill prevention and containment action for those who produce or store Biodiesel exists. Discharge of animal fats and vegetable oil are order of magnitude less toxic than petroleum discharge, do not create carcinogenic compounds and, are really biodegradable by bacteria thus minimizing physical impact on environment.

Nevertheless, extreme discharges of animal fats, vegetable oils and Biodiesel can cause negative impact on aquatic life. Biodiesel spills compare more favorably to petroleum oil spills. Moreover, likelihood of a vegetable oil or Biodiesel oil spill being comparable in magnitude to a petroleum spill is also very small due to differences in volumes in the two industries. Petroleum tankers exceed 2,50,000 ton capacity whereas vegetable oils are carried in tankers with 3,500 to 5,000 tons capacity.

There is a need to differentiate between the vegetable oils and petroleum oil through the creation of separate classes for animal fats and vegetable oils from petroleum oils, and apply separate standards based on the differences in physical characteristics between the classes. Biodiesel is currently controlled in the same manner as animal fats, vegetable oils and petroleum oils are controlled under oil spill laws and regulations, Biodiesel facilities and tanker vessels transporting Biodiesel remain controlled in the same manner as if they were petroleum oil facilities or tanker vessels transporting petroleum oil.