A sulfuric acid drain cleaner can be an effective tool for cleaning a clogged drain, but it also can be incredibly dangerous. It is simple to use, readily available in low concentrations and can chemically break down many materials, as well as generating some heat to melt blockages. On the other hand, it also emits fumes, is corrosive, can cause serious harm if it touches the skin and can cause death if used improperly. If a sulfuric acid drain cleaner is used in strict accordance with all recommended safety precautions, then many of the concerns involved in using the chemical can be put to rest, although there might always be some factors that are either unknown or beyond the user's control that could cause a disaster.
One of the main benefits in using a sulfuric acid drain cleaner is that it has the ability to remove nearly any reasonable clog, with the exception of very heavy, solid clogs that are caused by inorganic materials. It also does not require any special training to use, because it is simply poured into a drain and left to work until the clog is gone. A cleaner with a sulfuric acid base also is very convenient and economical, because leftovers can be stored for later use, and it can be applied to any drain that can be reached without requiring space for tools.
There also are a number of disadvantages to using a sulfuric acid drain cleaner. The largest one is that sulfuric acid is a highly toxic, caustic material that will emit harmful fumes the second it is exposed to air. These fumes can cause severe eye irritation and have the potential to burn the tissue inside the nose and lungs if inhaled deeply. The fumes will persist in the room in which the cleaner is used in until it has flushed out of the drain, requiring good ventilation in the meantime.
Another consideration when using a sulfuric acid drain cleaner is that the same chemical effect that causes the cleaner to easily dissolve the matter in a clog also will dissolve nearly anything it comes in contact with over time, including skin and clothing. Once the acid has been poured into a drain, it must be left alone until the acid has worked. If the clog does not clear out, then the acid will be left in the drain and could cause problems for a plumber who arrives later to clear it. It also cannot be used in drains with garbage disposals or other devices that have the potential to splash the acid back outside the drain.
Most importantly, sulfuric acid drain cleaner has a very powerful chemical reaction when it meets water or some other drain-cleaning chemicals. It generates heat that could cause violent explosions or eruptions of toxic fumes, so it can really only be applied to a mostly dry drain. This is one reason why sulfuric acid solutions with higher concentrations of the chemical are regulated and only available to professional plumbers.
Even once a clog has been cleared, sulfuric acid drain cleaner could still cause problems. It has the potential to kill the necessary bacteria in a septic system and it can cause pipes to corrode. Sulfuric acid also can cause environmental problems, depending on the type of sewage system in an area where it is used.