Masks, masks and more masks

How big is a germ? How tight does my mask have to fit to repel germs? We looked at these questions and more. 

According to an Agri-Facts factsheet published by Alberta Agriculture (Agdex 086-8), the two main classes of respirators are air-purifying respirators and atmosphere-supplying respirators.

Air-purifying respirators (APRs) are the most common. They depend on the users breathing to draw air in through the filter. They remove contaminants from the air with cartridges or canisters before the air reaches the person.

APRs should only be used in an environment that has enough oxygen to sustain life. A half-mask only covers the nose and mouth. A full-face mask covers the nose, mouth and eyes and should be used if the hazard irritates the skin or eyes.

Atmosphere-supplying respirators have fresh filtered air blown in to the user. They must be used instead of air-purifying respirators in these situations:

  • oxygen-deficient environment such as silos and manure pits
  • contaminant level is high beyond the capability of the air-purifying respirator to capture and filter it
  • contaminant is highly toxic

The Kansas agricultural department adds to the information provided by Alberta. It warns that there is no single type of respirator appropriate for all work situations. It’s critical to identify the correct respiratory protective equipment for each situation. The Kansas farm and ranch extension service divides atmospheric contaminants into three categories:

  • particulate contaminants include dust, mist and fumes that can be inhaled
  • gases and vapours that are gaseous at room temperature, such as those found in silos and manure pits. Vapours are released from liquid applications such as pesticides, paints adhesives
  • oxygen-deficient atmosphere is a danger when oxygen levels are as low as five percent in such areas as sealed silos, manure storage facilities and controlled atmospheric storage for fruits and vegetables.

Pennsylvania State goes into greater detail in defining the various types of masks and respirators.

Nuisance dust masks are constructed of light filter paper. A single thin elastic band circles your head to secure the mask. This type of mask provides protection against large dust particles, but little to no protection against smaller airborne particles. Wear this type of mask only if you are working on a short-term task involving nontoxic dust, such as sweeping the shop floor. A nuisance dust mask is not a respirator. A nuisance dust mask is not adequate for general farm service.

The following descriptions will help determine whether you need air-purifying respirators or atmosphere-supplying respirators for your work.

Disposable particulate respirators are commonly referred to as dust masks. They should not be confused with a nuisance dust mask. Main uses for the disposable particulate respirator include protection from dusts, mists, and some fumes in jobs such as haying, applying fertilizer and grinding feed.

This is a molded mask that covers the nose and mouth, held in place by two elastic straps. The filter is made of fibrous material that traps particles as you inhale. This type of respirator can be disposable or reusable, but should be disposed of when saturated with a liquid. Replace the filter of a disposable mask when:

  • breathing becomes difficult
  • the mask loses its shape
  • the mask does not seal to your face
  • you can taste or smell a substance known to be in the air

Chemical cartridge respirators use an absorbent material such as activated charcoal to absorb contaminants and filter out low concentrations of toxic gases and vapours. A full-face mask provides eye and face protection and offers greater protection against contaminants.

A chemical cartridge respirator consists of a soft silicone facepiece that covers the nose and mouth and a valve to regulate air movement through the filter. This type of respirator is appropriate for areas that have vapours and dust because these respirators can be equipped with different filters. The filtering cartridge generally screws into the front of the mask. You can select and insert the correct cartridge for the type of gas or vapour contaminant in your work area.

Combination cartridges are designed to provide both gas/vapour and particulates protection in a cartridge. For example, if you wanted to protect yourself from formaldehyde and residual airborne particulate matter, the most appropriate choice would be the 3M 60925 Formaldehyde & P100 Cartridge. Most respirator manufacturers offer such combination cartridges.

When heavy particulate filtration is required, you may consider a standard gas/vapour respirator cartridge in combination with a respirator pre-filter, as opposed to the combination cartridge. This configuration is commonly used in applications involving spray paint or pesticides. Examples of a respirator pre-filter include the 3M 5P71 P95 Respirator Filters and 3M 501 Filter Retainer. This configuration allows the wearer to replace the particulate filter as frequently as needed without having to also replace the gas and vapour cartridge.

Keep in mind, you must buy a mask and cartridge by the same manufacturer. For instance, a 3M half-face/full-face will only function properly if used in tandem with 3M cartridges.

Replace cartridges when you begin to smell or taste the contaminant, a situation called “breakthrough” or when dizziness or irritation occurs. Do not use a chemical cartridge respirator in areas that may contain gases designated as immediately dangerous to life or health.

Gas masks are also called chemical canister respirators. The canister holds more chemical absorbent than a chemical cartridge, thus they can be used in areas where gases are extremely toxic or highly concentrated. The canister can be mounted on a person’s belt, worn on the back or chest, or screwed onto the mask at the chin and connected to the facepiece via an air hose.

Positive pressure powered air-purifying respirators (PAPR) are different from respirators that require human breathing to move air. A PAPR is equipped with a motorized blower that forces air through the filter. For this reason, PAPRs are also called “positive-pressure respirators.” This type of respirator is recommended for people with respiratory impairments or cardiovascular conditions.

Most PAPRs have a hard helmet and rigid visor, although half-masks and full-face models with nonrigid helmets are also available. A PAPR with a full-face mask or closable hood provides the greatest protection against contaminants.

Depending on the filter, the PAPR can be used to provide protection against dusts, mists, gases and vapours. The constant flow of air makes the unit cooler for the user. This unit should not be worn in areas considered at risk if there’s a fatal breakthrough.

The two types of supplied-air respirators are air-line and self-contained breathing apparatus (SCBA). An air-line respirator provides clean air via a hose connected to a stationary air pump located in a clean-air area. SCBA is the other style. SCBA has a portable air tank carried on the back, similar to the unit carried by a scuba diver or firefighter.

Supplied-air respirators are expensive and require proper fit and maintenance to operate correctly. In addition, a user should receive instructions for using this type of respirator and should practice.

A supplied-air respirator is the only respirator that should be worn in an area considered at risk of a fatal accident, such as a manure pit or sealed silo.

Using a supplied-air respirator is the only safe way to enter such an area because of potentially dangerous gas and lack of oxygen. As a farmer, you risk your life by entering an oxygen-deficient atmosphere without a supplied-air respirator.


How big is a germ? How tight does my mask have to fit to repel germs? We looked at these questions and more.

  • Actually, there are no germs. It’s all a big mistake dating back to the Romans, who used the word “germen” meaning seed or sprout or “germinate”. They thought germs were little seeds.
  • The idea that disease-spreading organisms could pass from person to person existed as far back as ancient Greece.
  • Today, we use the word “germ” as a catch-all term that covers bacteria, viruses, fungi, protists, prions, amoebas and any other microscopic particle that cause illness in humans.
  • Bacteria are microscopic single-celled organisms, many of which don’t cause diseases. They live on the tops of mountains to the deepest sea vents. They live in water, soil, the air, clouds, your carpet, the ocean, and inside your body.
  • Some bacteria cause disease. Once pathogenic bacteria enter your body, there are a variety of ways they can cause illness. Some species cause infection of open wounds, others proliferate in your kidneys causing urinary tract infections, some affect the spinal cord causing bacterial meningitis. Still others only grow in fluid inside the lungs leading to bacterial pneumonia. Antibiotics only kill bacteria, which is why a doctor won’t prescribe antibiotics for viruses, such as the flu or common cold.
  • Viruses are smaller than bacteria. The largest virus is still smaller than the smallest bacteria, therefore more difficult to filter out with a mask or respirator.
  • A virus consists of a small piece of DNA or RNA genetic material surrounded by a small protein capsule. They basically float around until they bump into a compatible cell. Then they attach themselves to the target cell and inject their genetic material. The naïve cell is tricked into replicating the virus’s DNA, using the instructions it contains to build more viruses. The newly created viruses explode out of the cell, perpetuating the process, thus spreading the disease.
  • Unlike bacteria, viruses cannot survive, reproduce or self-replicate without a host. That’s why scientists debate whether viruses are objects or organisms, whether they are alive or not.
  • In the Middle Ages, during the time of the Black Death, the prevailing theory held that rotting organic matter created a vaporous mist filled with disease-causing particles. It was believed that breathing “bad air” was the cause of disease. They weren’t far off the mark.
  • The famous Crimean War nurse Florence Nightingale was a proponent of that ancient theory. Her idea that foul-smelling vapours caused illness led to hospital sanitary reforms.
  • In the late 1800s, the “bad air” gradually was replaced by germ theory thanks mainly to the experiments of Louis Pasteur and Robert Koch.
  • As to the question of how tight your mask should fit, the answer is simple: Tight as you can get it. If you feel air seeping in or out, then COVID-19 virus germs can also move through it.
  • In buying or building a mask, remember the virus can be as small as 0.5 micron. Those half-micron viruses can slide in through your N95 mask when inhaling if it doesn’t fit tight enough. And they can blast out if you cough or sneeze.

Source: Sabrina Stierwalt, Professor of Physics at Occidental College

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