Histotechnology Safety in the Histology Department

Flashcards covering chemical, biological, mechanical, and fire safety regulations, exposure limits, and waste management protocols in the histology laboratory.

What three requirements must be detailed in institutional and laboratory SOPs as part of an exposure control plan?

Housekeeping details, personnel protection, and waste disposal.

Which laboratory tasks place personnel at risk of exposure to blood or potentially infectious materials?

Frozen sectioning, autopsy, gross dissection, handling fresh tissue/body fluids, and cytology preparation.

What are the four major classes of hazards encountered by staff working in histology?

Biological/infectious, mechanical, chemical, and health/physical.

What solutions can be used for disinfection against HIV in the histology lab?

$1\%$ Bleach, $2\%$ glutaraldehyde, formaldehyde, and ethanol.

Why is the Hepatitis B vaccine required for laboratory employees with continuous blood exposure, and when should antibody titres be evaluated?

Hepatitis B is the most frequently encountered laboratory-associated infection ($7\times$ greater in lab personnel); antibody titres should be checked $30$ to $60\,\text{days}$ post-vaccination.

Which disinfectants are recommended for Hepatitis B Virus (HBV)?

$1\%$ Bleach, formaldehyde, $70\%$ ethanol, and $2\%$ alkalinized glutaraldehyde.

What conditions of moist heat are required to inactivate Tuberculosis (TB)?

Moist heat at $121^\circ\text{C}$ for $15\,\text{minutes}$.

Which disinfectants require longer contact times to effectively inactivate Mycobacterium tuberculosis?

Formaldehyde and $1\%$ bleach.

Why should cryogenic sprays be avoided on frozen sections or poorly fixed tissue?

They generate infectious aerosols that increase exposure to airborne pathogens such as TB.

What are prions, and what pathologic brain alteration do they produce in CJD/vCJD?

Prions are abnormal proteins ("Proteinaceous infectious particles") that cause spongiform encephalopathy, creating a porous, sponge-like structure in the white matter of the brain.

In which histological preparation stages has CJD been proven to remain infectious?

Well-fixed tissues, paraffin blocks, and stained slides.

What chemical treatments are effective against prions?

$5\%$ sodium hypochlorite for $2\,\text{hours}$, concentrated formic acid for $1\,\text{hour}$, or $1\,\text{N}$ sodium hydroxide for $1\,\text{hour}$.

What autoclaving parameters are required or preferred to inactivate prions?

Autoclaving at $121^\circ\text{C}$ for $1\,\text{hour}$, though increasing the temperature to $132^\circ\text{C}\text{ to }134^\circ\text{C}$ for $1\,\text{hour}$ is preferred.

What are the four classifications of infectious waste in histology?

1. Pathologic material specimens, 2. Blood, 3. Microbiological or culture specimens, and 4. Sharp objects.

What is the recommended disposal method for pathologic waste compared to other infectious waste?

Only incineration is recommended for pathologic waste, whereas steam sterilization or incineration is recommended for all other infectious waste.

What design criteria are required for sharps containers used as engineering controls?

They must be puncture-resistant, closable, color-coded, upright, and mounted at a height where the technologist can view the contents.

Which repetitive tasks in histology are most commonly associated with musculoskeletal ergonomic injuries?

Coverslipping, manual microtomy, opening cassettes, and the use of forceps.

How is Time-Weighted Average (TWA) defined?

The average airborne concentration of a substance over a specified period, typically an $8\text{-hour}$ work shift, intended to protect against chronic exposure.

What is the formaldehyde Action Level, and what does it mandate?

$0.5\,\text{ppm}$ as an $8\text{-hour}$ TWA; it triggers additional exposure monitoring and medical surveillance programs.

What is the Permissible Exposure Limit (PEL) for formaldehyde?

$0.75\,\text{ppm}$ as an $8\text{-hour}$ TWA.

What is the Short-Term Exposure Limit (STEL) for formaldehyde and how is it sampled?

$2.0\,\text{ppm}$ averaged over a $15\text{-minute}$ period, measured $4\,\text{times}$ daily with at least $1\,\text{hour}$ between exposures.

What is a Ceiling Limit (CL) in chemical safety monitoring?

The concentration that must never be exceeded at any time during the work shift; it has no exposure time limit and protects against immediate toxic effects.

What adverse respiratory outcomes occur when airborne formaldehyde concentrations reach $10\text{ to }20\,\text{ppm}$ versus $> 20\,\text{ppm}$?

Concentrations of $10\text{ to }20\,\text{ppm}$ cause difficulty breathing, while concentrations $> 20\,\text{ppm}$ can cause pulmonary edema.

What dangerous compound is produced when formaldehyde reacts with hydrochloric acid (HCl)?

Bis-chloromethyl ether vapor, which is highly carcinogenic.

How does "toxic dose low" differ from "toxic concentration low"?

"Toxic dose low" is the lowest dose of a substance producing any toxic effect in humans by any route other than inhalation; if toxic by inhalation, it is termed "toxic concentration low."

What is the definition of $LD_{50}$?

The calculated dose of a chemical expected to cause the death of $50\%$ of an experimental animal population through exposure by any route except inhalation.

What is the primary physical hazard of picric acid, and how must it be maintained in the laboratory?

It is impact-sensitive and explosive in dry form (similar to TNT); it must always be stored wet/damp and inspected regularly.

Why are ethers categorized as insidious chemical hazards, and what precaution must be observed after opening them?

They oxidize with air and light exposure to form shock-sensitive explosive peroxides; opened containers must be discarded after $6\,\text{months}$.

What is the maximum permissible volume of flammable liquids stored outside of an approved storage cabinet?

A maximum of $10\,\text{gallons}$ stored in approved containers.

What requirement must be met before disposing of acids and bases down the sanitary sewer?

They must be neutralized to between $\text{pH } 3$ and $\text{pH } 11$ with water running.

Which metallic compounds must NEVER be disposed of into the sewer system?

Mercury, chromium, and silver.

What is the definition of flash point (FP)?

The lowest temperature at which sufficient vapors are produced to form an ignitable mixture with air near the surface of the liquid or container.

What materials are involved in Class A fires, and what extinguishing agents are used?

Ordinary combustibles such as paper, wood, textiles, and plastics; extinguished using water, water-based solutions, or dry chemicals.

What fuels a Class B fire, and how must it be extinguished?

Flammable liquids and gases; extinguished by blocking oxygen using dry chemical or carbon dioxide ($CO_2$).

What defines a Class C fire, and what agents are suitable for extinguishing it?

Electrical fires; extinguished using nonconductive agents such as carbon dioxide ($CO_2$), dry chemical, or Halotron (Halon).

What defines a Class D fire, and how must it be handled?

Fires involving combustible and reactive metals (metallic sodium, potassium, lithium, magnesium); extinguished only with an agent specific to the type of metal.

What do the numerical ratings from $0$ to $4$ indicate in the NFPA system?

$0 = \text{None}$, $1 = \text{Slight}$, $2 = \text{Moderate}$, $3 = \text{Severe}$, and $4 = \text{Extreme}$.

What hazard classes are represented by this WHMIS/GHS pictogram?

Flammables, pyrophorics, self-heating substances, substances emitting flammable gas, self-reactives, and organic peroxides.

What specific health hazard classifications are indicated by this WHMIS/GHS pictogram?

Carcinogen, mutagenicity, reproductive toxicity, respiratory sensitizer, target organ toxicity, and aspiration toxicity.

In the NFPA 704 standard diamond shown, what hazard is represented by each color section?

Red represents Flammability, Blue represents Health, Yellow represents Instability (Reactivity), and White represents Special hazards.