Fortunately, ethanol is not generally considered to be a dangerous material. It can cause harm, even death, but the circumstances needed for that are not usually met and harm from ethanol is not a major concern in histotechnology.

Much ethanol is manufactured by distillation from fermentation of sugar by yeast, although it can be manufactured from other sources, such as oil, in chemical processes. Ethanol made industrially from fermentation should not be considered comparable to that made in small batches for human consumption as whiskey, vodka and so on. The scale is much larger, and the likelihood of some non-potable contamination is of concern. These aspects are strictly controlled in authorized distilleries for the production of drinking ethanol and the products are potable. This may not be true in the case of ethanol produced industrially for industrial purposes.

It is not unknown for laboratory workers to dilute some ethanol for consumption on the basis that ethanol is just ethanol and when diluted with water it is the same as vodka. It is not the same, and some words of caution are needed.

The process is much the same for potable or industrial production except for the scale. A sugar source is fermented with yeast, and the low-concentration ethanol is then distilled. It may be distilled more than once to get the maximum concentration of ethanol possible. From these solutions of water and ethanol only, ethanol of about 95% may be obtained. To get higher concentrations of ethanol, other materials may be added, and this may be of major concern if the resulting ethanol is consumed. The other material used is usually benzene, and from a mixture of ethanol, water and benzene distillation can produce 100% ethanol, or as near to it as makes no difference. It does mean, however, that 100% ethanol contains trace amounts of benzene, a known carcinogen. This kind of ethanol should never be consumed.

Ethanol has been controlled by many governments throughout the world, some ban its sale and consumption completely while others tax it to varying degrees. So those having a legitimate need for high-concentration ethanol may use it without paying tax. Some governments make it available without tax if it is adulterated to make it undrinkable. A common means of adulteration is to add methanol, and this mixture has given rise to the name “methylated spirits”. Today, materials other than methanol may be used and it is more properly named “denatured alcohol”.

Denatured alcohol is usually relatively easy to obtain, and is suitable for dehydration during paraffin processing. Whether it is suitable for other purposes should be determined by trial in a specific case, but it often is. It is usually possible to obtain unadulterated ethanols but doing so comes with some inconvenience, as strict record-keeping is usually involved.

A second concern with ethanol is its flammability. This is particularly so as modern automatic tissue processors often have heated chambers to improve dehydration and clearing. Firefighting materials should always be readily available for use when needed, although large fires should be left for professional firefighters.

Ethanol spills may be cleaned up by soaking into a cloth or paper towels, then washing out the cloth and wiping down the area with a wet cloth. Other than sufficiently large quantities of water being used, no further treatment is necessary.

The disposal of used ethanol may be problematic, although many jurisdictions permit it to be discharged into their wastewater systems. The amount may be reduced by redistilling if your jurisdiction permits that. Recovered ethanol may be used during the dehydration step in processing. Keep in mind that both waste and recovered ethanols may be contaminated with materials from the tissues dehydrated.