Every time you take a breath, air rushes into your lungs where hundreds of millions of delicate little sacks, called alveoli, enable life-sustaining oxygen to enter the blood stream before it is transported throughout the body to each living cell. While it is easy to take breathing for granted, maintaining a healthy respiratory system is essential. Unfortunately, the by-products of industry produce a multitude of airborne chemicals, gasses, dust, and particles which can easily damage the sensitive tissues of the respiratory system. Some of these resulting in illness and even death.
Respirators are an effective means of protecting the whole of the respiratory system. Respirators work by sealing off the nose and mouth from the environment and only allow air to enter which has passed through a filter to remove harmful substances. Unfortunately, many do not fully comprehend that the defense respirators provide depends heavily on whether it fits the wearer well.
Airborne hazards and your lungs
Industrial environments are often rife with airborne hazards, both organic and inorganic. Some hazards, such as toxic gasses, pass through your lungs into your circulatory system and can cause systemic issues. Other hazards, such as asbestos, spores, and silica dust cause damage to the lung tissue. To understand how these airborne hazards cause disease, and why it is so important to protect against inhaling these hazards, it is first important to understand how the lungs function.
Think of the lungs as an upside-down tree. After passing down the trunk of the tree, your trachea, the lungs split of into two large branches – the left and right lung. Each branch continues to split off into more branches, then finally splits into hundreds of thousands of tiny twigs. Like leaves on a tree, each of these twigs are covered in tiny sacks of air, the alveoli. These air sacks fill up every time you breath and are responsible for transporting oxygen into your blood stream. Each alveolus is lined with tiny capillaries the width of a single blood cell. Air diffuses through the wall of the alveolus into this capillary where red blood cells pick up life-sustaining oxygen molecules. The reverse operation is how the body expels carbon-dioxide.
To enable diffusion of oxygen, the tissues of the alveoli must be thin and delicate. Unfortunately, these tissues can be easily damaged by infection, harmful particles, spores, dust, and chemicals. Airborne hazards can cause inflammation and scarring of these delicate tissues, and this scarring means oxygen and carbon dioxide can no longer diffuse across the barrier. The more alveoli which are damaged, the less oxygen gets into your body. With enough exposure, so much of the lung’s alveoli will be damaged that there is not enough oxygen to sustain life.
“if a gap exists between the respirator and the wearer, air suddenly has a new path”
Airborne hazards can cause other harm to the lungs as well. Irritation from airborne hazards can cause inflammation in the lungs. Many hazards are also carcinogenic, increasing your likelihood of developing cancer. A great way to understand the many harmful effects airborne hazards can have on the body is to examine the impact of smoking tobacco. Smoking tobacco is particularly damaging because it involves combustion and contains a mix of over 7,000 chemicals which make their way throughout the body. The carcinogenic compounds in tobacco smoke increase the smoker’s chance of cancer all over the body, including, of course, the lungs. In addition, the carbon monoxide of tobacco smoke compromises the primary function of the respiratory system by displacing oxygen in the blood.
Respiratory hazards can also damage the upper parts of the respiratory tract. For instance, smoking damages the little hairs, cilia, which line the respiratory tract. When healthy, these move mucus up and out of the respiratory tract. Respiratory hazards, such as smoking, can kill these little hairs. With no cilia, mucus cannot be easily moved out of the lung. This process contributes to microbial infections and the further breakdown of lung tissue and eventual scarring, and this scarring can result stiffening of the lungs which impede breathing. The fragile alveoli can also become infected, leading to damage and eventual death. In many cases, the damaged portions of the lung cannot repair themselves. This means damage from airborne hazards can be permanent and irreversible.
This should convince anyone of the importance of protecting the lungs from airborne hazards. The best way to protect the lungs is to block the hazardous substances from entering the body. Respirators are an effective way of doing this if, and only if, the respirator fits well.
Importance of fit
For a respirator to fully protect you, all incoming air must pass through a set of filters which remove targeted harmful substances. Passing air through a filter creates resistance, making breathing through a filter harder than breathing normally. If a gap exists between the respirator and the wearer, air suddenly has a new path of lower resistance; instead of struggling to make its way through a filter, air easily and quickly flows through the gap. This is bad news for the wearer, as air coming through the gap still contains harmful substances.
Leaks are usually caused by a gap, although they can also be caused by a defect in the respirator. If the respirator does not fit you correctly, little gaps between the contours of the face and the seal of the respirator will develop through which unfiltered air can easily pass. The larger the gaps, the less air will be forced through the filter of the respirator.
Unfortunately, fitting a device to the human face, especially fitting one around the nose and mouth, is a difficult engineering challenge. The face is made up of multiple convex and concave planes, many of which may move and change shape as we talk, smile, or make facial expressions. Each face is also unique, so a one-size-fits all model simply does not work. Not only will the bone structure, width of nose, and shape of the chin affect the way a respirator fits, the amount of fat beneath the skin also impacts the fit of a respirator. In a recent study on the fit of N95 masks, our research team discovered that the respirators which fit adult children often did not fit their parents, even when both had similar facial structures. As we get older or lose weight, the layer of fat beneath our skin becomes thinner. This changes the way a respirator will fit, meaning a respirator which fit you when you were younger may not provide a good fit twenty or thirty years later, or after gaining or losing weight.
Sadly, humans have a poor ability to ascertain if a respirator fits. Multiple studies have shown that even experienced heath care workers cannot tell if a respirator fits properly. People tend to overestimate the fit of their respirator and miss small gaps which result in compromised protection. Thus, it is essential that each new respirator be fit tested to ensure there are no leaks.
Fit testing should be performed every time you get a new make, size, or model of respirator to ensure it fits properly. Respirators come in many different designs and sizes, and it is unlikely that all will fit any one person. Fit testing is done to ensure the respirator you will be wearing in a hazardous environment seals to your face and does not allow unfiltered air to enter your body.
So how big must a leak be to be a problem? The answer to that question depends on many factors, such as how big the hazardous airborne gas or particulate is, how quickly the user is breathing, and the location of the leak, to name a few. Some research suggests that gaps as small as a pinhead can compromise the protection of a respirator! This helps explain why fit testing is so essential.
Types of respirators
There are several types of respirators, and each has its own risk of fit issues. The three main types of respirators are:
1. Full-face respirators, which have a rubberised seal and cover the eyes, nose, and mouth
2. Half-face respirators, which have a rubberised seal and cover the nose and mouth
3. Filtering facepiece respirators, which are disposable respirators that cover the nose and mouth
How easily and well a respirator fits seems to depend on the type of material utilised in its construction as well as its shape. Both full-face and half-face respirators have a flexible, rubber-like gasket at the edges which secure to the contours of the face creating a good seal. The flexible nature of this aids in maintaining a good seal, compensating movement of the face and body.
These respirators are outfitted with filter cartridges or continuous supplied air. If continuous supplied air is used, a positive air pressure will prevent hazardous air from entering the mask. These types of respirators do not usually need to be fit tested and will normally have a loose fit. Respirators with rubberized seals often uses built in filters or changeable filter cartridges. Filter cartridges provide flexibility, as they can be changed depending on the type of airborne hazard present. These cartridges are colour coded for identification and should be replaced after a predetermined amount of time or exposure. When performing fit testing, it is important the correct type of cartridge is utilised, as some fit testing methods will provide accurate results only when a certain type of cartridge is used. For example, if banana oil is to be used as a qualitative fit testing agent, an organic vapour cartridge must be installed.
“research suggests that gaps as small as a pinhead can compromise the protection of a respirator”
Other commonly used types of respirators are filtering facepiece respirators, such as dust masks, N95 masks, and FFP1/2/3 respirators. Unfortunately, these respirators can be quite difficult to fit. Commonly, the only contact between the respirator and the skin is usually the border of the respirator, which in some cases can be quite narrow, and most importantly, does not function like a gasket. This makes it easier for a leak to develop, either during testing or while performing occupational tasks. Some respirators have a flange to help prevent this problem, but the fit of filtering facepiece respirators tends to be less reliable than the fit of respirators with thicker, flexible gaskets. In a recent study from Cambridge University, seven people each tried on five different models of filtering facepiece respirators. Only three of the seven people were able to find a respirator which fit them correctly. Out of the 35 fit tests performed, only seven had an adequate fit.
How fit testing is performed
There are two main methods by which fit testing is performed: quantitative and qualitative.
Quantitative fit testing uses a machine to measure and compare the number of particles in the air and inside and outside the respirator. Quantitative fit testing takes place in an enclosed space, such as a small or medium sized room. Sodium (salt) is aerosolised to generate airborne particles for the mask to filter. A thin tube is connected to the respirator. This allows air samples to be taken from inside the respirator while it is being worn. If the respirator fits correctly, air inside the respirator should have no or very few particles. Another tube collects samples of the surrounding, unfiltered air. A particle counter takes in air from both tubes and calculates how many particles are in each. The particle counter then compares these filtered and unfiltered samples to calculate what is known as fit factor. The fit factor score is a measure of how well a respirator fit. If no particles are found inside the mask, the mask fits well and no air is leaking in. If, however, even a small number of particles are found inside the respirator, this indicates there is a leak somewhere caused by poor fit.
“qualitative fit testing is not as accurate as quantitative fit testing”
Qualitative fit testing is not as accurate as quantitative fit testing; nonetheless, qualitative fit testing is an OSHA approved method of testing fit. Qualitative fit testing relies on the test subject being able to detect the taste or smell of a substance, depending on the type of respirator and filter used. If a respirator fits, these substances are filtered resulting in an absence of taste or smell. If, on the other hand, there is a leak in the respirator, the substance enters the respirator and is detected through smell or taste.
The type of substance used depends on which type of respirator one is using and which type of filter that respirator is equipped with. When testing filtering facepiece respirators, such as an FFP1/2/3 respirator, a bitter or sweet solution is used. When testing respirators with filters that can handle organic vapours, isoamyl acetate (also known as Banana Oil) is also used. The test procedure involves placing a small hood over the head of the test subject wearing the respirator in order to concentrate the test solution which is nebulised or aerosolised into the hood. Any taste or smell detected by the test subject indicates that the respirator does not fit properly. Most test subjects can taste or smell the test solution when not wearing a respirator. Research has shown that some people simply cannot taste or smell certain substances used for qualitative fit testing. In these cases, a different substance or quantitative fit testing must be used.
Movement and fit
The way you move can have a great effect on how well a respirator fits. Just think of how much your face moves when you talk, smile, or laugh. The skin around your mouth stretches, crinkles, and compresses. When smiling, your cheeks raise up and your eyes crinkle. While talking, your jaw moves up and down, changing the shape of your face. Although these actions may seem minor, they change the shape of your face and thus the way a respirator will fit. Physical action can also impact if a respirator fits. Running, bending, turning our head, and nodding all exert pressure on the respirator, which can cause it to move out of place.
Standard fit testing procedures try and simulate such daily activities. While performing a fit test, the test subject is usually asked to perform a set of actions which may involve jogging in place, reading or speaking normally, bending over, and turning the head. These activities seek to simulate the normal range of occupational activity.
Both qualitative and quantitative fit testing utilises a mix of activities. If the respirator’s fit is compromised while performing one or more activities, it may not be the respirator for you.
It may be worth thinking about the types of activities you regularly do while wearing respiratory protection. If you do something not simulated by the test, it may be worth mentioning to the person conducting your fit testing. It is also good to pay attention to how your respirator feels while you work. If you notice the respirator sliding around or feeling lose while performing an activity, it should be brought to the attention of the relevant safety professional.
Vulnerabilities and new horizons
Although fit testing is very effective, there remains room for improvement. Qualitative fit testing can be more expensive, as it requires the purchase purchase or rental of expensive fit testing machines and adapter cartridges. Qualitative fit testing is less accurate than quantitative fit testing; some studies suggest qualitative fit testing has an 80% accuracy. While this may be sufficient for some applications, many occupations require complete certainty that a respirator fits. Both forms of fit testing must be conducted by someone who has received training in how to administer the test and record and interpret the data.
As the science of respiratory protection continues to advance, new concerns and new technologies evolve. One troublesome assertion some researchers have made is that the protection achieved during fit testing may not accurately represent the degree of protection the wearer gains in occupational settings. Fit testing is performed in a controlled setting using substances different from the hazardous ones encountered in the occupational environment. In addition, the activity panel used during fit testing may not accurately reflect the activity experienced during occupational work. This is a potential problem even with quantitative fit testing. Performing quantitative fit testing in the occupational environment has been suggested to improve accuracy, although the machinery required for the testing makes this unrealistic in some situations. Fortunately, the science of respiratory protection is rapidly growing at present as scientists and engineers across the world tackle the new challenges the SARS-CoV-2 viral epidemic has highlighted. New technologies to assess the fit of respirators are being proposed and tested, and the future may see a whole new way of fit testing. Respirator design is also undergoing rapid innovation, with technologies such as 3D scanning and printing offering the potential for respirators with a custom fit. Yet for now, fit testing remains the best way to ensure the respirator you are using is a good fit for you.