Understanding respiratory hazards

- [Instructor] The organ in our bodies that is most sensitive to small particle exposure is our respiratory system. Breathing in particles that at sufficient concentrations are toxic to our body can have immediate, acute effects, or it can cause chronic or longterm health conditions, or both. When it comes to identifying particles that might be hazardous to our respiratory system, particle size matters. The smaller the particle, the longer it can float around and stay in the air, and as particles become smaller, they have the ability to penetrate deep into the gas exchange region of our lungs when we inhale them. Let's take a closer look. When looking at particle sizes, it helps to refer to things that are familiar to us, so let's do that. Remember we're looking at very small particles here, so the largest thing I'll start with is a grain of sand. Very course sand can be the in range of 1000 to 2000 micrometers in size. Very fine sand is about 60 micrometers. Sawdust can range from 600 all the way down to 30 micrometers, so we're getting smaller now. Much smaller than you'd be able to see without, say, a microscope. Particles of silt which can be described as extremely fine dust are about 10 micrometers in diameter, which is the same size as what we call respiratory droplets, the droplets that we expel when we cough. Let's stop here and start to apply some health terms to these particle sizes. The first term I'll talk about is inhalable. Particles that are considered inhalable are less than 100 micrometers in diameter. Inhalable means that these particles can make it into our nose and mouth when we breathe. Getting smaller, thoracic particles are smaller than 25 micrometers, and these are the ones that can make it into our upper respiratory airways when we breathe them in. Last we have respirable particles. These are the ones that are so small that they can make it all the way into the gas exchange region of our lungs, and these particles are defined as being about five micrometers or smaller. Particles this size and smaller can include spores, bacteria, and viruses. To get inert particles down to the size where they fit that definition of respirable generally takes some sort of processing. Let me tell you what I mean here. So, in my industry, construction, we're concerned with exposure to respirable crystalline silica. Those respirable particles of crystalline silica can be inhaled. They can make it all the way into the gas exchange region of our lungs, where they get stuck and they cause irreversible lung damage. But this is where particle size matters. Because crystalline silica does not naturally exist in a particle size that is small enough to be considered respirable. In fact silica's one of the most plentiful elements on the planet. The sand on the beach is mostly silica. I don't wear a respirator to the beach, because the particle sizes that exist in nature are too large to be respirable. They only become small enough to be dangerous through industrial activities like cutting or grinding products like concrete and asphalt that contains silica. So this issue of how the particles exist in the space around you also complicates the assessment, and that's true for biological particles as well. The individual bacteria that causes anthrax, for example, is smaller than one micrometer, but in nature those bacteria form spores larger than that. The other issue related to particle size is the length of time particles remain in the air. Particles larger than five micrometers, including those respiratory droplets that I mentioned are heavier than air, and they'll typically fall to the ground in seconds, and will only travel about two or three meters. The respirable particles that I discussed, the ones that are five micrometers and smaller? They can remain in the air for minutes to hours, and can travel much further. Particles this size, five micrometers and smaller, are considered to be aerosolized when they're dispersed into the air. So the conclusion that I'm getting to here is that respiratory hazards can be difficult to assess, because there can be many factors to take into consideration. There may be a dangerous particle or virus, or bacteria, but the question is, will it present itself in a form and a quantity where I could breathe it in and it's harmful? Or will I be doing something that could cause the particles to become aerosolized? In the case of working with products you purchase, like paints or solvents, or industrial gases, you should have an easy source of information in the Safety Data Sheets, which should clearly identify any respiratory hazards. But in the case of doing things like processing raw materials, cleaning up or demolishing an existing site, working in contaminated environments, or working with infected patients, it may be really difficult to assess the hazard without using the services of a trained professional. For example, an industrial hygienist, who has the knowledge, experience, and the equipment to do a proper hazard assessment.