Common Accidents in a Histopathology Lab

Hospital pathology laboratories are dangerous places to work due to the many hazardous chemicals employed during histology and molecular biology techniques, as well as equipment that contain sharp blades. Of the different kinds of laboratories located within a pathology setting, histology labs are where the most accidents—40 percent—occur.

In this article, I explore some examples of accidents that have occurred within the setting of histology/histopathology laboratories, and what you can do to avoid such accidents in your own laboratory.

Eye injuries caused by chemical fumes

The worst accident I’ve seen in a histology lab was when a medical student was heating paraformaldehyde in water to dissolve it. He was doing this work in a certified, chemical fume hood, in which he had placed a stirring heat plate and added the paraformaldehyde to the water, then added a stir bar and started to heat and stir the solution. He wanted to check to see if the paraformaldehyde solid had dissolved completely in the water, so he opened the sash of the fume hood and stuck his face over the large beaker of swirling, hot paraformaldehyde. The fumes from the hot liquid instantly glued his contacts to his eyes.

Safety equipment isn’t effective if not used correctly. The paraformaldehyde solution was being made inside a chemical fume hood, which is the proper procedure. But by sticking his face directly over the beaker, the fumes didn’t have an opportunity to be removed by the fume hood’s fan before making contact with his eyes. 

Paraformaldehyde should only be used in a certified, chemical fume hood. Other precautions to protect the user’s face include wearing unvented goggles (so there is no chance of fluid splashing through the goggles into the user’s eyes) and a face shield if there is the possibility of a large splash. Staff should never put their faces into a chemical fume hood or look at mixing chemicals inside the fume hood by placing their faces above the mixing solution.

Burns caused by acid splash

It is often necessary in a histopathology lab to dilute concentrated acid and bases. When doing so, it is important to add the acid or the base to the water, rather than the other way around. Most lab staff have understood this since they were undergrads and are very careful when mixing up solutions involving concentrated acids and bases. In fact, most lab staff likely take it for granted that all others in the lab are aware of the proper procedures for mixing up these solutions.

Unfortunately, I have encountered a new staff member in the lab who did not know how to safely mix these solutions. He added concentrated hydrochloric acid to a beaker and then proceeded to pour a large volume of water into the beaker. The fluid exploded, causing chemical burns to his face and forearms.

Lab managers should not take anything for granted when it comes to training lab staff on how to work safely in the lab. Teaching new staff even the most basic of safety precautions may save someone from being seriously injured.  

Explosion due to incompatible chemicals

Improper storage of chemicals accounts for nearly 25 percent of all lab accidents. Histopathology labs use many chemicals that are identified as hazardous, including flammables, irritants, corrosives, sensitizers, and toxic chemicals. When incompatible chemicals come into contact with each other, the results can be disastrous. Many of us may understand the dangers of combining incompatible chemicals, or storing them in close proximity to each other. But how many of us would question adding chemical waste to an empty container?

One lab worker added organic solvent waste to what he believed to be a clean, empty container in a chemical fume hood. He then capped the waste container, left it in the hood, and walked away. It turned out to be lucky that he walked away, because that seemingly clean and empty waste container actually contained nitric acid residue. Nitric acid is a strong oxidizer and organic solvents are highly flammable. The result was an explosion that caused a flash fire within the hood. The shock wave from the blast continued up through the hood ductwork and into the corridor where a secondary explosion blew out the false ceiling panels in the corridor. 

It’s important to understand chemical compatibilities in labs and to ensure that incompatible chemicals are properly segregated, to prevent them from coming into accidental contact with each other. Equally important is rinsing out waste bottles thoroughly prior to adding chemical waste. 

Amputation by microtome

A histology lab employee was setting up a paraffin block in the specimen-holder clamp of the microtome in her lab when she inadvertently activated the machine through a foot pedal. Her left hand came into contact with the knife, which amputated the tip of her thumb and index finger. The employee was hospitalized and treated for her injury, which included bone loss.

It is important when using microtomes to always use the safety devices that are built into the instrument. Always shield the blade with the knife guard when not actively cutting sections and engage the hand wheel brake to prevent your fingers from getting caught in the microtome. It’s also critical that new staff who are unfamiliar with the operation and use of a microtome be carefully trained and monitored until they become proficient with the instrument and its safety features. 

Formaldehyde inhalation

Sometimes lab staff get so desensitized to the inherent safety risks of working in a histopathology lab (or any laboratory setting for that matter) that, after many years of experience, they do things they know to be unsafe.

A good example is the case I witnessed of a lab manager who was presented with an unlabeled, 2 ml tube of clear liquid by a staff member who was asking what the liquid was. In an effort to decode the unlabeled tube’s contents, the lab manager uncapped the tube, place it close to her nostril, closed the other nostril with her other hand and took a whiff, as she had numerous times before under similar circumstances. This time, however, there was a different outcome and the entire contents of the tube went straight up her nose. At this point, she knew with certainty that the mystery liquid was formaldehyde. The incident took place many years ago, but to this day, the lab manager still has no sensation at all in that nostril, which has now essentially been fixed in formaldehyde. 

The take home message from this incident is two-fold. First, we all know how important labeling is in the lab, but sometimes may find ourselves being overly lax about following through. It’s very important to always label containers, no matter how small, or how inert the contents may be, even if it’s just a balance tube filled with water. Second, no matter how skilled you may be in the lab, or how many years of experience you may have, never ease up on safety precautions. They are there to protect you, and senior lab staff owe it to the more junior staff to set an example by working safely in the lab. Becoming lax with safety procedures doesn’t do anyone any favors.