Grossing Hoods – The Front Line of Protection

Grossing Hoods – The Front Line of Protection

All laboratory personnel should be aware of and know what personal protective equipment (PPE) they should wear while performing various tasks in the histology laboratory.  Employers are responsible for educating laboratory personnel about what hazardous chemicals they might handle, how to handle them safely and what specific protective equipment to wear for each and every task that is performed in the laboratory.

Employers must make use of engineering controls to help protect workers as well.  In addition to the usual heating and cooling system of the work area, the histology laboratory should also have workstations that are vented to the outside, or make use of filters if vented back to the inside air.

Usually, there is at least one chemical fume hood located in the laboratory vented to the outside.  Employees can use this space to pour off flammable/noxious chemicals, coverslip, or perform special stains that may generate hazardous fumes (i.e. mixing hydrochloric acid with potassium ferrocyanide to make the working solution of the Gomori’s stain for iron).

Performing the surgical grossing of specimens is one task that requires both full PPE and a ventilated work station.  Laboratory employees must be protected against formaldehyde fumes and blood borne pathogens.  Most pathology laboratories make use of units referred to as “grossing stations”.  The most common grossing station is made of stainless steel which comprises the work surface, sides and front.  This accommodates ease of cleaning and disinfection.  Plumbing and a sink may be included for applications where large specimens (i.e. whole organs, limbs, etc.) are received.  Strong lighting is required as well.  Generally, a grossing station has a series of small exhaust fans (usually four) situated at the back of the work surface.  Since formaldehyde is heavier than air (i.e. vapor pressure = 1.1), these fans pull the formaldehyde vapors into the back of the station, where they are collected into one vertically rising duct.  The vapors are propelled along the inside of the duct with extra fans to move the vapors up the ductwork, to the outside of the building.  An important regulation is that the exhaust duct on the roof of the building must not be anywhere near any intake vents for the building ventilation.  Figure 1 shows an example of such a grossing station.

Another grossing station uses side and downdraft principles to manage heavy formaldehyde fumes.  Figure 2 shows how the intake fans pull the fumes sideways, and move then downward.  Once propelled downward, the fumes can go through a filter system to remove the hazardous fumes.  This clean air can now be moved back into the laboratory.  Clearly, the filters must be changed on a regular basis, according to the manufacturer’s recommendations.  It is important to select the exact grossing station configuration that will work the best for your laboratory.



[Author’s note: Please be aware that OSHA’s regulatory standard 29 CFR Part 1910 describes exactly what employers and employees need to know with regard to Personal Protective Equipment (PPE), including mechanical controls.  The entire standard can be found on the OSHA website.  The following bullet points are taken from 29 CFR 1910.132 for your information, as an addendum to this article.]

29 CFR 1910.132    General Requirements

Application. Protective equipment, including personal protective equipment for eyes, face, head, and extremities, protective clothing, respiratory devices, and protective shields and barriers, shall be provided, used, and maintained in a sanitary and reliable condition wherever it is necessary by reason of hazards of processes or environment, chemical hazards, radiological hazards, or mechanical irritants encountered in a manner capable of causing injury or impairment in the function of any part of the body through absorption, inhalation or physical contact.


Design. All personal protective equipment shall be of safe design and construction for the work to be performed.


Select PPE that properly fits each affected employee

The employer shall verify that the required workplace hazard assessment has been performed through a written certification that identifies the workplace evaluated; the person certifying that the evaluation has been performed; the date(s) of the hazard assessment; and, which identifies the document as a certification of hazard assessment.


Defective and damaged equipment. Defective or damaged personal protective equipment shall not be used.


  1. Theory and Practice of Histological Techniques. JD Bancroft, A Stevens ed. Churchill Livingstone, NY.  Fourth edition. 1996
  2. Theory and Practice of Histotechnology.  DC Sheehan, BB Hrapchak.  CV Mosby Company, St. Louis. First edition. 1980.
  3. Dermatopathology Laboratory Techniques.  CM Chapman, I Dimenstein.  2016.
  4. Dapson and Dapson.  Hazardous Materials in the Histopathology Laboratory.  Anatech Ltd.

Your participation with comments and questions are much appreciated. They may just help other histotechs.

Bar Code Tracking in Histology

Specimen volumes continue to increase in both hospital and private pathology histology laboratories.  Histology laboratories must adopt new procedures and strategies for managing this increasing volume of specimens to ensure the highest quality of patient care.  Integration of new equipment and technologies for better management of all histology specimens is crucial.

Within the hospital pathology laboratory a standard protocol is to make certain to never assign consecutive accession numbers to the same tissue type.  That is, the accessioning department would accession a skin specimen, then perhaps a liver specimen, before accessioning another skin specimen.  This is the first in a long line of procedures developed to maintain specimen integrity from specimen receipt through final sign out of the report – a built in “double check” mechanism.

Private laboratories may not have this option.  Usually, the majority, if not all, of the specimens are skin tissue.  Therefore, it is the rule, rather than the exception, that there are many skin specimens accessioned consecutively.  The integration and utilization of a bar code tracking system is one method of helping to ensure 100% accuracy in specimen identification.

The first opportunity for a unique specimen checkpoint is during the accessioning of the specimen. During accessioning, a unique two dimensional (2D) bar code label is affixed to (1) the specimen requisition, (2) the specimen bottles, and (3) each specimen cassette.  When the surgical grossing process begins, the first step is to scan the 2D bar code on the requisition, the specimen bottle and the cassette.  The information must match on all three items.  If it does not, the laboratory information system (LIS) will not allow the grossing technician to continue.  This procedure insures 100% accuracy with regard to the identity of the tissue within the cassette.

When used in conjunction with a bar coding identification / tracking system, the information from standardized surgical grossing techniques can be used to help maintain specimen integrity.  During accessioning and grossing, patient and specimen information, in the form of a 2D bar code, are applied to the requisition and grossing cassette.  Tissue processing cassettes are then placed into the tissue processor.

After processing, during the embedding phase, each cassette is removed one at a time from the holding well.  The 2D bar code on the cassette is scanned, and the case information appears on the screen of the LIS.  This information includes the gross description of the specimen type, along with the number of pieces of tissue in the cassette.  Having access to this information is critically important to the embedding histologist.  The information in the LIS can be double checked against exactly what is in the cassette, with regard to number of tissue pieces and specimen type.  This step guarantees 100% accuracy of the specimen information at the embedding phase.

After the embedding is completed, the solidified blocks are taken out of the embedding molds, and any excess paraffin is removed from the block.  This step is documented by scanning the 2D bar code on the block, and indicates that the blocks are now on a cold tray, in a refrigerator, waiting for microtomy.

The microtomy phase begins when a histologist removes a cold tray, containing blocks, from the refrigerator and takes it to their microtomy work station.  The microtomy work station is standardized, and each histologist must follow the block cutting procedure exactly.  Workflow is unidirectional; a block designated for cutting moves in only one direction, into and out of the microtome cutting area.  In addition to the unidirectional workflow, the only labelled slides present in the work envelope are those for the block that is being cut.

Scanning the 2D bar code on the block time stamps the block as being “cut”.  It also provides the histologist with the case information in the LIS, which is used to generate a unique slide label. The scans in the microtomy phase provide two additional check points to ensure specimen integrity, and “one piece’ work flow.

The block is cut into paraffin sections which are picked up on the corresponding microscope slide.  Once a block is cut, it moves into the “block done” box – never back to the “block to be cut” area.  The slides are placed into the “slides done” rack and moved into the oven for heating in order to remove water and melt the paraffin, thereby attaching the sections to the slides.  When this microtomy procedure is followed, it ensures 100% accuracy with regard to the cut tissue matching the slide label information.  Accidental “switching” of slides is not possible.  The block is now logged as being “cut” in the LIS system.

Racks of mounted and baked slides for routine hematoxylin and eosin (H&E) staining are brought to the H&E slide staining area.  After staining and coverslipping, each slide is visually inspected and checked against the corresponding block to provide a final check on specimen accuracy.  The 2D bar code on the slide is scanned to indicate “slide checked”.  Additionally, slides are checked for H&E stain quality, and the results documented on a log sheet.  Specifically, nuclei must appear blue with chromatin material visible, with eosin staining in the cytoplasm resulting in three shades of pink. The slides can now be brought to the office area for interpretation by the pathologist.

In summary, constant vigilance is required in the histology laboratory in order to guarantee specimen integrity.  This vigilance can be enhanced to a greater degree by using a bar code tracking system.  This Bar code tracking technology is recommended by the College of American Pathologists and the National Society for Histotechnology (4). In combination, bar code tracking and human diligence can result in an increase in patient care quality – a goal that all laboratorians should strive for.


  1. Theory and Practice of Histological Techniques. Chapter 10.  JD Bancroft, A Stevens ed.  Churchill Livingstone, NY.  Fourth edition. 1996
  2. Theory and Practice of Histotechnology.  Chapter 9.   DC Sheehan, BB Hrapchak.  CV Mosby Company, St. Louis. First edition. 1980.
  3. Chapman CM: Barcoding and Dermatopathology.  Advance for Medical Laboratory Professionals: Vol. 23 No 9, May 9, 2011.
  4. Brown et al.  Uniform Labeling of Blocks and Slides in Surgical Pathology.  Guideline from the College of American Pathologists Pathology and Laboratory Quality Center and the National Society for Histotechnology.  Arch Pathol Lab Med.  Accepted for publication March 12, 2015.

Microwave Devices – Why can’t I use a microwave oven that I can buy from an appliance store? Part 2

This blog is Part 2 on microwave devices. Please check the website for Part 1 of the blog where regulations and safety issues related to microwave devices are explained.

When I was shopping for a new kitchen microwave for my home, there seemed to be hundreds of models with different wattage, sizes, features, etc. These kitchen microwave ovens are useful for cooking at home, but better consistency and quality is necessary when working with patient tissue.


  1. Exposure Cycle: Most kitchen microwaves have a 30 second cycle. That means, if you set the exposure at half-power, the magnetron is on for 15 seconds, and off for 15 seconds. It does NOT mean that if you have a 1000 watt microwave at half power, it is now a 500 watt microwave. It means the power is on for half the cycle time. Let’s say you heat your coplin jar for 1 minute at half-power. That’s 15 sec on, 15 sec off, 15 sec on, 15 sec off, for a total of 30 seconds on. However, the solution in the coplin jar is cooling for the last 15 seconds of off time. So after 1 minute, the temperature may read 60 degrees C, but after 45 seconds it may have reached 70 degrees C and then cooled off 10 degrees during the last 15 seconds. Laboratory microwave devices are different, in that they have cycles of 1-2 seconds, with some having continuous power, allowing better cut off time, and thus better control of the final temperature.
  2. Hot and Cold Spots: Kitchen microwaves are designed to heat casseroles and other yummy meals. The magnetron releases beams of microwaves in a grid pattern, so that there are concentrations of beams in a low, wide pattern, similar to the size and shape of the casserole dish. What is the shape of a coplin jar? Tall and thin. If a corner of the food gets a little too cold or a little too hot, we can still eat it. But what about patient tissue that gets a little too hot, or not hot enough? That’s why we have to pour-off-pour-on the solutions in the coplin jar when heating in the kitchen microwave. The laboratory microwave has concentration of beams more evenly dispersed over the entire chamber (side to side, and top to bottom) so there are no hot and cold spots.
  3. Temperature probe: Most kitchen microwaves do not come with temperature probes. As a result, a histotech would have to rely on time to bring the solution up to a certain temperature (see Quality/Consistency #1). Most laboratory microwave devices come with a temperature probe, so you can program it to reach exactly, say, 60 degrees C, before cutting off.
  4. Agitation: With kitchen microwaves producing hot and cold spots, maybe the bottom half of the tall coplin jar gets too hot, or maybe the top half does. Either way, with a kitchen microwave, the histotech usually stops the microwave halfway through the cycle, pours the solution off and on the slides to mix it up, and then heats it for the remaining time, and again repeats the off and on pouring to mix the solution. With a laboratory microwave, there is a “bubbler” built into the temperature probe, so the solution is stirred the entire time it is being heated.
  5. Power and time settings: Kitchen microwave settings are not highly accurate. If the timer is off by 5 seconds, or the wattage is 50 W higher than the setting it is no big deal when heating food. We eat around the overcooked or undercooked areas. This kind of inaccuracy is not acceptable when staining slides or processing tissue. Laboratory microwave devices are designed with much more accuracy in the settings.

I hope I have given you enough information so that you can justify the additional cost of a laboratory grade microwave device.

Microwave Devices – Why can’t I use a microwave oven that I can buy from an appliance store? Part 1

I still get asked this question, particularly by people whose lab is becoming CAP accredited for the first time and they are suddenly confronted with a non-compliance citation by the CAP. Laboratory microwave oven specification standards are strictly regulated by federal agencies governing laboratory safety. CLSI addresses the standards in publication GP-281 “Microwave Use in the Histology Laboratory”, which summarily states that kitchen microwave ovens are forbidden in the laboratory setting. OSHA regulation 29CFR1910.303(b)(2) addresses the laboratory microwave oven standards by stating that lab equipment is to be used in accordance with the manufacturer’s instructions. Underwriters Laboratories safety instruction UL 923 for the common kitchen microwave oven states “Use this appliance only for its intended use as described in the manual. Do not use corrosive chemicals or vapors in this appliance. This type of oven is specifically designed to heat, cook, or dry food. It is not designed for industrial or laboratory use.

So why did all these agencies decide that kitchen microwave ovens cannot be used in the histology laboratory? Two main reasons: they are designed with inadequate Safety features and they cannot produce Consistency and Quality to the degree required in laboratory procedures for reliable results.


1. Seal: The seal around the door of a kitchen microwave device was designed for food vapors, not chemical vapors. The laboratory microwave device was designed for chemical exposure, though the quality of the seal should still be checked every year, to see if there is breakdown of the seal, or leaking of microwaves.

2. Ventilation: Kitchen microwaves vent the fumes out into the atmosphere. This is no problem when food is being heated. In a laboratory however, fumes from silver nitrate or alcohol should never be released into the laboratory, exposing lab techs. Laboratory grade  microwave ovens are constructed to vent the fumes through the laboratories ventilation system.

3. Electrical: The electrical system  of a kitchen microwave oven is not insulated from flammable vapors. Laboratory chemicals inside the chamber, especially being heated, release flammable vapors that would likely cause a fire or explosion. The electrical system of a laboratory microwave is designed so there is no exposure to flammable vapors.

The next blog will cover the Consistency/Quality issues related to microwave devices (Part 2).


– Bancroft JD and Gamble M: Theory and Practice of Histological Techniques, 5th edition, 2002, Chapter 19 “Application of Microwave Technology to Histology” by Steven Slap

What Should The Blade Angle Be On My Microtome?

What should the blade angle be on my microtome? When I set the blade angle at one place on the marks of the blade holder, it works for company X’s blades. But I got some trial blades from company Y, and they wouldn’t cut a ribbon, until I changed angles. Why?

Think of it like the steering wheel in a car. What is the ONE correct height and angle? Doesn’t it depend upon the height of the person, the girth of the person, the make of the car, the angle of the seat, and what feels right (it works) for that person?

So the first thing to realize is that the marks on the side of the blade holder do not mean anything. They are simply reference marks. They do notindicate degrees of angles.

BEVEL ANGLE: Think of the shiny edge of the blade – the bevel. If you looked at it from the side of the blade, the bevel comes to a point, similar to a triangle. This is the bevel angle. If you are using a sturdier blade, the base of the triangle is wider across, so the bevel angle at the tip is a larger number, than if you were using a thinner blade, which is narrower across the base and thus has a smaller bevel angle. The thinner blade is less sturdy, so it can’t cut harder tissue, but probably gives you a nicer ribbon.

CLEARANCE ANGLE: The marks on the side of the blade holder are reference points for clearance angle. This is the angle between the front face of the block and the one side of the bevel triangle that is facing the block. Normally, this bevel angle should be between 3-8 degrees. The smaller the clearance angle, the sharper but less sturdy the blade is. Conversely, the larger the clearance angle, the sturdier the blade but less sharp it is. So the “correct” angle depends upon what type of tissue is being cut (need for sturdiness) and how thin the section needs to be (need for sharpness).

CHANGING ANGLES: Let’s say you were using a thicker, sturdier blade, with a wider bevel angle, and had set the clearance angle at 5 degrees. If you switched over to the thinner, sharper blade with the narrower bevel angle, but didn’t move anything else (didn’t move the angle), the new clearance angle would be wider, say 6 or 7 degrees, because of the thinner bevel.

This is what is happening when you change from one vendor’s blade to another. The bevel angle may not be exactly the same, so therefore the clearance angle is not the same as you were using. In addition, the height of the blade may not be exactly the same.


  1. Contact the manufacturers: Both the vendor who sold you the microtome and the vendor who wants to sell you their blades, want you to be able to microtome. Tell them the vendor microtome you have, and the vendor blade you are using. They should be able to tell you which mark on the blade holder usually works the best. You may have to adjust it a mark up or down, to get the blade to work right for you.
  2. Test out the microtome yourself: Start with a plain block of paraffin, or a block with non-dense tissue in it. Set the blade angle to the highest setting (e.g., 10). Try getting a ribbon. If that doesn’t work, lower it one mark. Try again. Keep doing this, until you are getting good, strong ribbons without bunching. Now try is with other blocks with various types and sizes of tissue, and at different thicknesses. Adjust the angle a little bit either direction, as needed.

You will soon have the best clearance angle for the way YOU cut YOUR tissue on YOUR microtome with YOUR blade!

What Other Departments do I Need to Contact, if I’m Buying a Piece of Equipment?

Congratulations on being able to buy equipment for your laboratory! Usually, the supervisor has looked into several vendors’ versions of the equipment, researched cost (outright and down the road), and looked to see if it would fit in allotted space. Then comes the matter to convincing department manager that there is a need to spend the money. But what other departments might need to be contacted, way before the decision to buy is made?

ENGINEERING: Get a drawing of the area – floors, walls, ceiling. It helps to find water lines, electrical lines, etc. It will also help to plot out if there is the right location – does it add steps to the workflow, do you have to back-track, go in a different room, etc.? Can you find extra space that you hadn’t considered for storage of new supplies? And remember, drawings are not always accurate, so check!

What size electrical line? Where should it be hooked in? Where are the nearest plugs? How easy, and at what cost, is it going to take to drop another line right there.

And what about running water – hot or cold, does it need to be at a regulated temperature? What about drainage? Can the trap and the pipes handle the type of chemicals coming out of the equipment?

How big is the equipment? How heavy? Will the counter/floor be able to handle the equipment? Will it fit through the door? In the elevator?

VENTILATION: Maybe this is Maintenance, maybe you need to bring in an outside company. What is your current ventilation in that area? What direction will the fumes be going – past the noses and the eyes of the people using the equipment? If a large piece of equipment is placed there, what direction will the air flow be going now? Are the fumes heavier than air, so a backdraft ventilation is needed? What is the material in the ventilation ducts? Can it handle the chemicals coming from the equipment?

SAFETY: What chemicals are being used? Is there anything radioactive? Is the equipment UL tested? Is there enough electrical power? What happens if there is a 6” flood of water in the room? Or water pouring from the ceiling? What type of safety training will need to be done for the people using the equipment? Are there SDS (Safety Data Sheets) available? How much space is required to allow people to pass through in case of an evacuation? Any ergonomic issues?

WASTE MANAGEMENT:  This may be part of your Safety Department. In your locale, what are you allowed to pour down the sink? How much per day/week/month/year? If you cannot dispose of the waste down the sink, is there a company that Safety is currently working, with willing to haul the waste away? At what cost? Is there a way to neutralize the material first? How labor intensive? What safety concerns for the people neutralizing the material? At what cost? What if there is a spill on the floor – where is the floor drain? How fast can the water treatment plant be notified about a spill into the waste water line? Is there a way to prevent the spill from getting to the drain, such as putting the recycler or the tissue processor in a large “spill pan”?

INSURANCE/RISK MANAGEMENT: Is there going to be an increase in the possibility of a flood, fire, waste release, etc? How much is that going to cost in additional insurance? Is there a better location to reduce these risks? What types of alarms will be needed if there is a problem? Who should be notified?

FIRE MARSHAL: Have a fresh set of eyes look at electrical equipment, evacuation routes, rescue routes, and let the fire marshal know what new chemicals are coming into the laboratory.

It is much better to get all these departments involved early in the decision making, rather than AFTER the equipment has been bought and is now setting in the hall outside your lab.