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Controlling Chemical Hazards

PACE credits are no longer available for webinars more than 6 months old.


Histology is an occupation that potentially places employees at risk of exposure to chemical hazards. Appropriate hazard and exposure assessment procedures are necessary to protect ourselves and assure a safe working environment for everyone. This webinar is designed to familiarize participants with signs/symptoms of exposure, permissible exposure levels and training. Hazard assessment and routes of exposure will be used to determine engineering controls, appropriate work practices and personal protective equipment.

Learning Objectives:

  1. Recognize potential chemical hazards in the workplace.
  2. Evaluate hazard assessment and control measure.
  3. Develop appropriate safe work practices to lessen or eliminate exposure.

Webinar Transcription

Maureen Doran B.A., M.S., HTL (ASCP):

We're going to take a look at our chemical hazard assessment. This is where we start with proper identification. Because chemicals can have many synonyms, we're going to refer to or list what we called the chemical abstract numbers, abbreviated CAS, to identify the proper chemical. Our safety data sheets list CAS numbers along with other hazard information and also now include the global harmonization system, GHS, as classification and labeling of chemical hazards. This system uses pictograms, warnings, and numbers to help us identify these hazards. On the bottom here you can see some of the familiar placards that we see on our labeling, flammable, corrosive, and oxidizer.


When we look at our chemical hazard assessment, we're going to focus first on our exposure. How does this exposure occur? A concentrated chemical we would think would be more likely to increase our exposure than if it was diluted. And maybe using smaller volumes of chemicals may decrease the exposure hazard. If the duration of exposure is prolonged, we may have to increase our protective equipment such as selecting a pair of gloves that may be a little bit thicker or even changing the material. Heating a chemical or changing the pH may also affect the hazard by increasing the acidic alkalinity of the solution. Or, it may make it more volatile or even more penetrating through our glove material. We’ll focus on our routes of exposure. So in our lab, we're mostly going to consider the first two here, inhalation and absorption. Usually, ingestion and injection are not an issue if we're using good laboratory practices. We know that inhalation is how most of our liquid or volatile chemicals are going to have access to our body. And absorption, we have a lot of chemicals that will have dermal exposure and will be able to be assimilated into our body.

The first group that we are going to concentrate on is our flammables. Flammables are defined by a specific characteristics and one of them is flashpoint. Flashpoint is the lowest temperature of the flammable liquid at which it gives off vapor sufficient to form an ignitable mixture with air near the surface of the liquid. In histology lab, flammable liquids comprise the largest volume of our reagents and a category we have the most contact with on a routine basis. Because of this, it’s very easy to become complacent when handling flammables.

We're going to talk a little bit about what our exposure limits are to all of our chemicals. Usually, I refer to these as occupational exposure limits and are usually expressed as threshold limit values. There’s actually four categories that we commonly use. The first one is our time weighted average. This is for an eight hour workday for 40 hours a week. And the value here assumes that you can be exposed to this chemical at this level for eight hours a day, 40 hours a week all year and not experience any adverse health effects. Of course, this does not include those people that may be hypersensitive to the chemical.

The next one is short term exposure limit, sometimes abbreviated as STEL. This is a 15 minute exposure. It should not be more than four times a day and it can never exceed the time weighted average. The other one that we’re going to look at is our ceiling value. And this is a concentration that should never be exceeded at any time. The last one is our biological exposure indices. This is sometimes abbreviated as BEI and this represents a concentration of chemicals in the body that correspond to exposure. So this measurement is a concentration of chemical markers in the human body, such as blood or urine, that indicate that we’ve been exposed.

Let’s take a look at some of our flammables here. As you can see on the left, we have listed our chemical abstract number. And then, on the right to the chemical, we either have a permissible exposure limit or a TWA. Ethanol usually is the one that has the highest exposure allowed in our lab and this is because of its low toxicity. Ethanol is processed in the body to CO2 and water. Mixing ethanol with isopropanol, remember, or mixing it with bleach can produce toxic fumes. This produces chloroform and hydrochloric acid. Exposure to ethanol and isopropanol can be increased if we add it to stains which we heat. And a good example of this is when we are making up our Luxol fast blue or Oil Red O, and we proceed to put these stains in the solvent in the oven or the microwave and therefore, we're increasing the volatility of the solvent.

You will notice that both isopropanol and methanol, although they are in the same group of solvents, have a much lower exposure limit than ethanol. That is because methanol is a cumulative poison in the body. It’s oxidized to formaldehyde and formic acid. Its target organ is the central nervous system, as the other ones are. But isopropanol can be absorbed through dermal exposure much more than both methanol and ethanol. Isopropanol is metabolized to acetone in the body. Now let’s consider that most of us, when we’re using our tissue processor, are not using 100% ethanol. Usually, we are using reagent grade alcohol, which contains both methanol and isopropanol in 5% each. Since these have the same effect on the same organ system as ethanol, we actually have a lower exposure limit to reagent alcohol then we would to hundred percent ethanol.

We also want to look a little bit here at our iso pentane. This is actually the most flammable solvent that we have in our lab. It has permissible exposure limit a little less than ethanol up 600 ppm. It’s often used as a quick freeze technique for frozen tissue and it’s noted that its flashpoint is so low that it usually is right at its boiling point even at room temperature. Here’s a list of some other flammable liquids that we also deal with in our lab. You’ll notice that pyridine is listed here and it has a very low permissible exposure limit. And that is because this one is actually toxic by inhalation. Its chronic exposure can cause central nervous system depression, G.I. upset, liver and kidney damage. 6 to 10 ppm cause headache and nausea, so those are our signs and symptoms of exposure.

There was, in 2005, a chemical spill in Belgium of only 2.5 L of pyridine. It came in a package in the package had been damaged. They left the package on the floor and there was a little bit of spillage. And they went through the whole shift and no one cleaned it up. By the time the night shift came through, two people had noticed this noxious smell because it smells sort of like fish. They went to clean it up and those two individuals actually experienced enough of the fumes that they passed out. So they transported them to the hospital. By the time it was all said and done, 51 people had to be treated for exposure. So this was very expensive and if they had just cleaned it up to begin with, it wouldn’t have been that big of an issue.

We have a picture here of the ductless fume hood and is a container of pyridine in front of it. So if you use these types of fumes systems, remember that they are limited in their use. They have charcoal filters and those filters are very good for a lot of solvents, like ethanol and isopropanol. However, they are not adequate for pyridine because it’s an amine. It goes through the filters and it goes right back out into the lab environment. Also, when you're using these ductless fume systems, remember that if you have a spill, you need to clean it up immediately because it can very quickly concentrate those vapors in there and saturate the filters that are being used.

You also see toluene and xylene. Xylene will have a permissible exposure limit of 100 ppm whereas toluene, which is 60% of most of our mounting medias, is only 20 ppm. So when we're using these solvents, we want to use our engineering controls. Here you have an example of a fume hood being used when someone is using the fixative Carnoy’s. They have a large volume here and unfortunately, they have it too close to the edge. So we want to have it behind the sash. We want the sash lower than the chin. We want it 6 inches from the opening. And we want to be concerned about the chemical mixtures. So in Carnoy’s, the fixative, 60% of it is ethanol, 10% is acetic acid and 30% is chloroform. So you want to remember, chloroform is a group 2 possible carcinogen and the odor threshold is the point where we would, if you can smell it, you're probably way over your permissible exposure limit.

Ethanol increases the volatility of the chloroform and the acetic acid, of course, makes it corrosive. Chloroform is metabolized to a toxic metabolite in our bodies called phosgene. Since the effect is on the same organ system, there is an additive result and it lowers the permissible exposure limit even more. So if chloroform has a permissible exposure limit of 10 ppm, because we added volatility, it’s going to be about half that.

Control plan for flammables

Let’s look at our exposure control plan for flammables. Of course, we make our determination and when we do this, you can’t say I don’t have any exposure because I’m always wearing protective gear. You do this determination as if there is no protective gear available and what am I going to do to protect myself. So list the tasks you could potentially be exposed to. And these are things like painting solutions and the stainers and the processors. There, we have our ethanols and xylenes, and even our xylene substitute. Cover slipping, again, we think about that we're not only cover slipping maybe from a solvent like xylene but we're also using the mounting media, which has that slightly more toxic chemical toluene and methyl methacrylate in it. We think about dispensing our flammable liquids. We might have exposure to more volume when we’re doing that. And also, where are we going to put the flammables when we're considering our hazardous waste?

So our standard operational procedures for flammable liquids is the same as with all our procedures. We want to get information so we look at our labels, our GHS system. We refer to our safety data sheets and also our reference material. We're going to use our engineering controls because we're mostly working with liquids here. We want to reduce inhalation exposure. If, for some reason, our engineering controls cannot meet with us to get below that permissible exposure limit, we’re going to have to use respirators. But remember, that’s our last line of defense.

We also want to be aware about signs and symptoms of exposure. With most of our flammables, it’s lightheadedness, headache, and dizziness. So again, we want to pick appropriate personal protective equipment and review our proper storage and emergency response. So again, engineering controls, those are our first line of defense. And we use ventilation hoods. However, most people have strong misconceptions regarding the efficiency of these devices. The regulating agencies all agree that the face velocity is not a determining factor for safety in hoods. Reliance on face velocity specifications for safety has no sound basis. In fact, it is the internal vortex that develops good performance and containment, not face velocity. Therefore, it is essential to have your hood performance tested.

Remember that if we are using things that are heavier than air, like most of our solvents that you can see in this picture down here, those vapors fall low. They can adjust the baffles in the back of your hood so that would take in more from a lower level and give you more of a containment when you're using those kind of solutions. And remember, the best safety device does not compensate for poor safety practices. Examples of the good work practices when using a ventilation hood are listed here. As seen here, as most flammables are heavier than air, they want to place the solution 6 inches from the opening so it contains the fumes. And keep in mind that competing airflows can disrupt this containment. Someone walking behind you can create as much as 300 feet per minute of a competing airflow and can draw that chemical into your breathing zone.

When we're storing our flammables, we usually are using flammable storage cabinets. So the National Fire Protection Agency and International Code Counsel have developed guidelines for the safe storage and use of flammable liquids that’s under a uniform fire code. Flammable storage room requirements are different from flammable dispensing room requirements. Structural considerations for flammable liquid indoor storage facility include a sprinkler system with two exit self closing doors and a 4 inch open grate trench to drain spills to a safe location. Ventilation should be at least 150 cfm. Storage should not exceed more than 10 gallons per square foot or about 3,000 gallons. The cost of upgrading or modifying an existing storage facility may be significant.

For indoor flammable dispensing, a grounding or bonding system must be in place. As you can see here, the technician is dispensing 100% alcohol out of a 55 gallon drum. So she must have it grounded so there is a metal core going from the 55 gallon drum to the proper wire that is grounded on the wall. There is also a cord that you can’t see that’s going from the drum actually to the container that she’s dispensing in. This is to prevent the buildup of static electricity. The NFPA 30 is enforceable by OSHA and European standards EN 14471.

Ventilation of a chemical storage cabinet is not required or even recommended. Venting storage cabinets has not been demonstrated to be necessary for fire protection purposes. Additionally, venting a cabinet could compromise the ability of the cabinet to adequately protect its contents from involvement in a fire, since the cabinets are not generally tested with venting.

So you may ask, I’m going to store my flammable liquids in the refrigerator. Do I really need a flammable or exposure proof refrigerator? Vapors from stored chemicals can come into contact with electrical spark that occur in the normal operation of a regular refrigerator. And these are the defrost timer, the thermostat switches, or the internal lighting unit. Once the vapor ignites, a powerful explosion can occur. Flammable storage refrigerators, like we see here, have no electrical sparking devices inside the cabinet. They're all located outside and you can see all the electronics are on top of this refrigerator in a contained little box. Explosion proof refrigerators are only required when storing flammable material in an area with an explosive atmosphere, such as a solvent dispensing room. They require special hazard location wiring rather than a simple cord and plug in connection.

These are actually pictures from a histology lab here in the United States. This article was published in the Histologic May 2003. These are pictures from 2002 where, in a histology lab, they were using isopentane to quick freeze in liquid nitrogen. The researcher wanted to reuse 50 mL of isopentane the next day and placed into a loosely capped 1 L bottle in a nonflammable refrigerator. In the early hours of the next day, at electrical spark ignited the vapors. The histology lab freezer door detached and was jettisoned 12 feet from the unit. As you can see, the damage was extensive. $165,000 does not include the facility cleanup, reconstruction, water damage to the floors below, loss of productivity, and data.

Fortunately, this occurred when no personnel were in the facility. And all this was caused by shortening the time of the experiment the next day by two minutes and saving two dollars worth of reagent. And this was not done by novice personnel. This same procedure have been done for many years by people that had worked in this lab for 15 and 20 years. So you might want to make sure that your non-rated refrigerator units are clearly marked as not approved for flammable liquids.

Going to take a look at corrosives. We all know that corrosives are capable of irreversible alterations in living tissue and chemical action at the site of contact. We also know that their ability to corrode metals is evident. In these two pictures, you can see corrosives have been stored in metal environments where they have caused a lot of corrosion. Acids we know have a low pH and they also have good warming properties. So when we come in contact with them at low levels, we’ll experience itching. If it’s more concentrated, we definitely will feel that burn very quickly. Whereas bases have a high pH, they feel slippery. They’re more difficult to remove and they have poor warming qualities. So they actually can also defat our skin as they burn and sometimes, you will get a much deeper burn before knowing that you actually come in contact with a base. Facilities for quick drenching or washing of the eyes and body for at least 15 minutes are required whenever the eyes or body of any person may be exposed to injurious corrosive materials.

Control plan for corrosives

The first one here is ammonium hydroxide. This is a strong base that we use often with our silver stains. So we’ll use it in our Fontana Masson, our Gomori’s Reticulin, and even our Steiner’s has a 1% solution of ammonium hydroxide in our developer. When we make these ammoniacal silver solutions, we’ve always heard that they possibly could be shock explosive. We want to remember that we don’t want them to dry out. Most of the information that we have regarding these ammoniacal silver solutions comes from the industry where they make mirrors. And their solutions are not that more concentrated than the solutions that we are using. And remember, a lot of these solutions we're also heating, so that also allows them to become more concentrated. By storing these solutions in a refrigerator, it does not prevent the formation of the explosive compound that occurs in these solutions, which is silver nitride.

But just because you’ve never heard of the stories of these things exploding in histology lab doesn’t mean it has not happened. And we have a good example of that. I’m just thinking back to our explosion with our isopentane. Formic acid is something that has a fairly low permissible exposure limit of 5 ppm. This is something that we use when we decal our bones and it’s also something that we use if we're going to inactivate some prions. So let’s make sure that we're aware of where we store our formic acid.

Other corrosive chemicals that we use are glacial acetic acid. This is very common. We add this to a lot of our stains and even it’s used in our common stains to acidify some of the solutions to make them work a little bit better. Oxalic acid is something we used in a melanin bleach method and we do have a little information of this from industry. There was a study in Norway that found that workers who were exposed to oxalic acid solutions in vapors revealed an increased prevalence in the formation of urinary stones. Also, hydrochloric acid is volatile and could emit a corrosive mist upon contact with the air. So inhalation damage can be to the respiratory tract.

Let’s take a look at our exposure control plans here with corrosives. Again, we're going to do our exposure determination as if we don’t have protective gear. So we're going to list the places where we could possibly be exposed. Preparing those staining solutions that have corrosives, cleaning our glassware, if we're still acid cleaning glassware for some of our silver stains, changing solutions in the stainer, so when they need to come off and we need to refresh them. Again, our bone calcification will use corrosives and then we want to consider how we’re going to store our corrosive waste safely.

As you can see here, someone is actually weighing out a corrosive. This is periodic acid as a powder and they're weighing it out on the scale. And then here, they’re using concentrated nitric acid and so they actually have a respirator on because their engineering controls are not adequate for decreasing their exposure in this instant. So we're using corrosive liquids again for our standard operational procedure, we're going to look at the same things to gather information. We’re going to again use our engineering controls and a respirator if the engineering controls are not adequate. And again, will focus on signs and symptoms. This is going to be mostly dermal exposure and respiratory exposure. And we’re going to look for the burning, itching, tearing. And were going to a select appropriate protective equipment to prevent this from happening.

We want to consider that the Bureau of Labor Statistics reports that eye injuries in the workplace cost over $300 million per year in loss of production time, medical expenses, and Workmen’s Compensation costs. Three out of every five workers injured were either not wearing eye protection at the time of the accident for wearing the wrong kind of eye protection in the lab. A single drop of corrosive may cause blindness within 2 to 10 seconds. And this is from direct destruction of the cornea. So let’s think about where are our eyewash stations? Do we properly check them? Do we make sure that our emergency equipment is working because we may not have that time to do that when there actually is an injury?

So remember, we want to make sure that we store all our corrosives below eye level and we want to use chemical splash goggles, not chemical glasses because they usually have openings that would allow a chemical to get into our eye if there was an accident to occur. We want to wear these when we're handling chemicals that are hazardous to our eyes, using chemicals that are unknown, or even working with liquids that are hotter than 60°. Remember, we also want to add a face shield if we are using concentrated chemicals or corrosives if we're using them more than 10 mL at a time. In this example here, they're dispensing from a 4 L bottle. They’ve added the face shield along with the chemical goggles.

In this picture here, the technician has selected a lot of appropriate gear and some not so appropriate. She has on her laboratory coat. She has on a thicker gauge of gloves to protect her from the acid, and she is in a fume hood and it’s pulled lower than her chin. But unfortunately, she has selected safety glasses instead of safety goggles. And we do have several instances, if there was a splash to occur that, it actually seeps down the edge of the glasses and can cause burning to the eyes. Again, we’re going to take a look at appropriate protective practices and equipment here.

In the picture on the left, you see the technician has safety goggles on, not safety glasses. She has a thicker gauge of gloves and her lab coat. And she is actually using a transfer bucket. This is secondary containment when transferring a concentrated corrosive. So in many times, most of our accidents with corrosives occurred during the transport from the storage facility to the ventilation hood where we're working with them. The bottle could slip out of your hands or possibly the little thumb ring breaks off. So secondary containment is a way of preventing this from happening. In the picture on the right here, you see in an example of inappropriate protective equipment. The young man here does not have safety goggles on. Yes, he’s not using a chemical yet but it’s coming to him during transport. He has gloves on but here, he does not have closed toed shoes on. And that is an issue in many of our labs, especially during the warmer months.

Waste disposal regulations will vary depending on our location. That being said, it is not good laboratory practice to use our sinks as dilution vats to dispose of corrosives. As we say dilution is not a solution. Remember that even though you're running copious amounts of water, these acids are heavier than water and they tend to accumulate in the drain area.

Control plan for reactive chemicals

We're going to move on to our reactive chemicals. And for us, in histology, these are mostly our oxidizers. Oxidizers are those reagents that are capable of starting fires without a source of ignition. They're defined as substances that yield oxygen to stimulate the combustion of organic matter. These are one of the things we want to keep separate, especially from our flammables. In this picture below here, you can see where they’ve actually stored oxidizers—this is an oxidizing acid, such as nitric acid—with some flammables. And what had happened, the doors were closed and the fumes from the two reagents had reacted, causing not only breakage from those bottles but also from the other bottles that were near it.

Here you can see with the oxidizer has leaked out from the small a bottle because it has a cork on it and it was not properly sealed, onto the metal and caused corrosion to the point where we were unable to determine what the chemical was in this bottle. So our global harmonization system will categorize oxidizers into several groups and as you can see, they use three groups of numbers here. Our H270 indicates that it may cause or intensify a fire, whereas an H271 says it may cause fire or explosion and it’s a stronger oxidizer. So when we look at our placards, we also want to look at the notes on there that will give us some more indication on what our chemical hazards are.

Here we have listed some examples of our oxidizers. The benzoyl peroxide which some of you may not know, is actually the catalyst for our JB4 or our glycol methacrylate. This is a very active catalyst and it needs to be handled very specifically. You never want to contaminate a catalyst with any other kind of reagent or actually utensils. Usually, when you’re weighing out this catalyst, you only use that utensil and you never use it for anything else because a very small amount of contamination can cause a very large reaction. The second chemical we have here is chromic acid. This is one we use often if we’re doing our fungus stain, our GMS. This actually has a fairly low permissible exposure limit. It’s an acid but it also is a very strong oxidizer.

Hydrogen peroxide is something that we use routinely in the lab if we doing immunohistochemistry. This is one that we usually take from a bottle that’s like 30% and we dilute it out to maybe .01 or even 1%. Periodic acid is an asset that we use quite often for our stain for our Schiff’s reagent. And then, we have picric acid. Picric acid is something that we use sometimes in a fixative for Bouin’s or Zamboni’s. But it’s also present in some of our special stains. Our Van Geisen stain has more picric acid in it than our Bouin’s does.

Some other reactive chemicals that we have our potassium permanganate. This is one that we use for melanin bleach. And then, we also have silver nitrate. This one is used in many of our silver stains, which we’ve talked about before. Uranyl nitrate is one that’s used in our Dieterle’s and also in a reticulum stain.

Let’s take a look at our exposure control plan for our oxidizers. Again, we want to make this determination on what tasks that we are going to do is going to expose us to these. Again, we’ll look at our fixatives, our special stains, our immunohistochemistry and again, our hazardous waste. And in this one particular, we want to be concerned with where we're going to dispose of these because they will react with some of our other reagents. Our standard operational procedure will include, again, determining what we can find out from our label, our safety data sheet, and also for our reference material. Again, using our engineering control to reduce inhalation exposure and what are our signs and symptoms of exposure because if we don’t know what those are, how can we evaluate our workplace to see if we're properly containing these? Select our appropriate personal protective equipment and again, what is our emergency response when we're handling these?

Here in this picture, you will see that they separated out all their oxidizers. They do have them in secondary containment. They have them in something that’s not reactive. It’s a small wooden cabinet. And there’s no combustible material, so there is no paper towels or lab paper or anything in with our oxidizers in this scenario here.

I’m going to talk a little bit about our glove selection here. But when we think about gloves, we don’t only want to think about thickness, and thickness is our gauge. We also want to think about our permeation rate and breakthrough time. So permeation rate is the diffusion of a chemical throughout the glove material and the breakthrough time is the time it requires that chemical to get to the inside of the glove. Now remember, both permeation rate and breakthrough time can occur without any degradation of the glove. So if you do find some contamination on your glove, just because you don’t feel it on the inside next to your skin, you still want to remove that glove and replace it and wash your hands, too, because this may have occurred without your knowledge. Some of the chemicals we work with do have delayed reaction. And remember, there is no universal protective material. All of these materials will degradate. It’s a matter of what time that it affords you protection.

Remember our work practices, changing gloves when they're contaminated, and not to, once you put the glove on, to touch things that would cause you exposure, like your face, your nose, other things like that. And avoid contamination of equipment that other people might touch with their bare hands.

This is an example of silver nitrate. We’ve talked about this as being at oxidizer. In this first picture here, there’s an example someone weighing out their silver, possibly to do one of their silver stains. They have lab paper down and they’re in a closed and balanced enclosure here. And then, they come back the next day and you can see that everyplace with the silver nitrate had fallen off the scale. It is oxidized to this black precipitate. And remember, this is a corrosive, so it’s not something that’s just there and looks ugly. It is damaging if someone were to touch this. If you remember, when we make up our silver solutions we put them in ammonium hydroxide, which makes that, in that basic solution, more penetrating to the skin. So if someone had spilled some ammoniacal silver on a counter and you had put your bare skin on it, you might notice some itching and then maybe you would go to the sink and wash it off. The next day, 24 to 48 hours, you would probably notice that the skin has turned black because the silver has oxidized at that point. You want to be concerned with unwanted oxidizer reactions. We want to avoid returning unused chemical to the original container.

Here in this picture, you see the tech extracting with a pipette some hydrogen peroxide for an IHT procedure. This is 30%. So she’s going to put it into another container and then dilute it. She is not going to return what she doesn’t use to that because this is an oxidizer. If there is a small amount of contaminant in that pipette, it could introduce something into that solution to cause an unwanted reaction. So remember, hydrogen peroxide is a peroxide former. If you're going to buy a bottle of 30%, you’ll notice in the cap, there is a little hole in the top so that some of that can come out. If you don’t have secondary containment around that, it’s going to take that oxidizer and place it on the outside of the bottle and so you’ll wonder, why does the label always disintegrate on my bottle of 30% hydrogen peroxide? That’s because the oxidizer is fuming around the label. So it’s a good idea to use secondary containment. If you’re going to store in the refrigerator, put it into a larger container so it’s not having those fumes come in contact with anything else in the area.

We're going to look a little bit at picric acid. This is one of our strongest oxidizers. This is our tri nitrile phenol and it actually only differs from TNT by hydrogen bond. Picric acid, as you can see in this bottom picture, actually cause an explosion in the 1800s of a factory where it was made. Several workers were killed and the factory was soon closed after that. It’s also used as a military explosive. So in the top picture here, you’ll see a technician who is weighing out picric acid to make Bouin’s and she is actually wiping the edge of the jar where the cap screws on to make sure there is no chemical residue there. So when she screws the cap back on, it will be clean because she doesn’t want it to dry out and therefore the friction of opening the bottle could cause a problem.

In the next picture here, this is actually a 5 gallon container of Bouin’s that is made up for a histology lab. And as you can see, there is some corrosion on the container because there was some leakage. In this facility, they had a concrete floor and actually, picric acid reacts with concrete violently. So you have to keep these apart. If you have concrete floors and you're using Bouin’s, make sure you use some secondary containment. Actually did have an incident where somebody had taken Bouin’s out to a farm to fix testes for animals and they dropped the glass container on the gravel going into the barn. That gravel had to be professionally scooped up, lab packed into a 55 gallon drum and disposed of. The cost was $4,300 to do that.

This is our potassium permanganate. This is one of those chemicals that we use in some of our stains. For example, it could be a replacement for our zinc or our mercury in our phosphotungstic acid stain. Potassium permanganate is an oxidizer that sometimes will react with some of the solvents we use in the lab and also with glycerin. And I know there are some comments that say that you could put these two things together and it’s just a myth that they actually react. It’s funny because actually, the firefighters use what they call Premo fireballs to fight fire with fire. A Premo fireball consists of 3 g of potassium permanganate and they add 1 mL of an automotive coolant ethylene glycol and they drop these. And they immediately start a counter fire.

So in this instance here, this is a laboratory situation where the technician was changing out the solutions in the processor and she was using a xylene substitute. She had previously weighed out potassium permanganate for phosphotungstic acid hematoxylin. Some of it is spilled but it was in the hood and it was on the laboratory paper. Well, she didn’t realize, when she was changing the solutions with her xylene substitute that also, some of the substitute had come in contact on the paper. And it didn’t do anything so, at the end of the day, they cleaned up. They wrapped up the paper and they threw it into the trashcan that you can see here on the edge. And as they were talking, getting ready to leave for the shift, all of a sudden, one of the technicians felt this warmth behind her. And they turned around and the entire trashcan was on fire. What had happened is, the solutions had dried out a little bit and allowed them to come in contact and therefore, started the fire with the potassium permanganate as being the oxidizer.

Another example we have here of our oxidizer incompatibility, this is a case that happened in the United States. They were working in a lab and they were reusing some of their hazardous waste bottles and didn’t realize that there was a significant amount of solvent in one of the hazardous waste bottles. And then, they used that same bottle to get rid of some nitric acid, which is a very strong oxidizer and as you can see, the bottom picture here is just a picture of the hood area where this explosion had occurred. And also, you can see the damage to the entire lab because it actually blew out the sash of the hood. There were two students that had to be transported to the hospital that did require medical treatment from this.

When we want to think about our emergency equipment when we're working with oxidizers, we want to remember that water may be the most effective way to contain an oxidizer fire. And you have to use copious amounts of water. So in the case of the potassium permanganate, they actually took the hose from the eyewash station on the sink and filled the entire trashcan with water to douse the flames. The oxidizer in non-miscible flammable liquids, you may just have to evacuate and isolate the fire. Dry chemical and carbon dioxide extinguishers are really not effective for oxidizer fires. And so this is something you need to be aware of if you have these in the lab, that this is something you’ll write in to your standard operational procedures. Remember that accidents and illness prevention is the responsibility shared by employees, managers, and the institution as a whole. And everyone needs to work together so that we can make a safer work environment.

Questions & Answers

The first is, do the barrels for disposal, which are 55 gallon drums, require a bond and ground? The barrels are heavy plastic or metal. The chemicals are held until the fourth barrel is full. And they are in a fire proof room. So do they require a bond and ground?

They require a bound and ground if you're dispensing out of them. Now if you are just pouring liquid in them, no.

Next, does a small tabletop fan, located 7 to 8 feet from the grossing station, interfere with the airflow of the grossing station?

That is something that an airflow specialist would have to determine. They have complicated equipment that will actually figure out if that’s competing enough with that grossing station to not have the fumes for the from the formaldehyde or whatever you’re using to come back into the work environment. I mean, enough difficulty because the people that are working in the station may think it’s better but it actually may be not the best for everyone else that’s working in the facility.

And this next question, I’m not sure exactly what she means or if you can answer it at the question is, what is the number for the splash goggles? I don’t think she means the phone number.

No, that’s actually an ANSI number and that comes from the regulation agency. And they do have a number on what the splash goggles are rated. And she is correct. They do have a number and I don’t see it right now. But it’s easily looked up on any of their websites.

Next question, how do I know if I’ve experienced symptoms of xylene exposure?

As we talked about, with most of the solvents, they are central nervous system and is the target organ and so symptoms usually are headache, dizziness, drowsiness, lethargy. And that being said, we can experience that on several days during the week, depending on what our workload is. What you want to look at is if the symptoms occur when you're exposed to higher volumes or tasks where you actually are changing out xylene or when you have your most exposure. And the other key element is, are you the only one that’s exhibiting these symptoms? So a marker to be concerned is if two or three of the lab personnel at the same time, if we change the processor every Friday, every Friday morning, we all get a headache. We all feel these same kind of symptoms. That’s an earmark that maybe we had an issue with exposure.

Speaking of gloves now, what type of glove is recommended when handling concentrated acids?

A lot of us in our histology labs, we use a lot of disposable nitrile gloves. And those gloves are usually a gauge or a thickness of either 3 to 4 mils. And those are adequate, usually, for splash resistance if we are using dilute assets anywhere between five and 10 minutes. When we go to concentrated acids when where measuring out things like hydrochloric or glacial acetic acid, they want to pick a heavier gauge and they recommend at least 8 mils. So that means you can double glove with two pairs of 4 mil gloves. Or you can look when you're purchasing gloves. A lot of them will sell the 8 mil gloves. And a lot of us like to put the 4 mil on the inside, 8 mil on the outside, depending on what your needs are. But definitely pay attention to that gauge when you're handling those more concentrated corrosives.

How do I handle combustible material contaminated with an oxidizer?

If you have worked with these combustibles and there is some spillage on disposable material, what you want to do is rinse that material, paper towels, lab paper, whatever into the waste container for that chemical so that you have rinsed it all out, so it’s no longer an issue to start a fire with that combustible.

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