Problems & Solutions

Published:  01 September, 2006

Question from an
industrial firefighter
Question: I heard that toxic gases and vapours from hazardous materials can get inside a self-contained breathing apparatus facepiece, even if you have a good seal between the mask and your face - is this true?

Question: I heard that toxic gases and vapours from hazardous materials can get inside a self-contained breathing apparatus facepiece, even if you have a good seal between the mask and your face - is this true?
Answer:
Yes, this can occur through the process known as permeation.  While it is possible, it rarely occurs during routine firefighting. However, if you deal with hazardous materials in higher concentration then the possibility increases quite a bit.  There are chemicals out there that can degrade the lens piece and the actual mask itself and that can also lead to a direct leak through the failure of a component of the facepiece, but for this discussion we will focus on the concept of permeation.
If you think about it, even though your facepiece is clear enough to see through, it is still made out of a material that is solid to the touch.  Facepieces for respirators are constructed from one of several different types of material. There are both natural and synthetic materials used for this purpose. 
However, all materials are comprised of molecules representing the actual chemical contents of the substance(s) used in the manufacturing process.  Each molecule of the clear material used in the lens of the facepiece, which you can see through, is a defined size and while they may be extremely small in size they still have a fixed size and shape.  As the chemical atoms bond into molecules and the molecules bond together they create a material, the product that your facepiece is made from.
In this case, the material happens to be see through, but none the less a solid.  When we look at a solid material at the molecular level one can see that there are indeed spaces between the molecules and that the electrical charges of the atoms that comprise the molecule hold the material together in a natural state of bonding.
As far as various toxic and hazardous vapors are concerned, each chemical has its own size and shape at the molecular level and the vapours comprised of these molecules also have a shape and size. 
If a hazardous product has a molecular size that is less that that of the open spaces between the molecules of the material that comprise your facepiece, then eventually (time weighted) if there is a high concentration of the product in the area of your facepiece’s lens exterior surface it may begin to weave its way through the molecular space of your facepiece lens or through the facepiece itself. 
How permeability can occur
Through the bonding process of the hazardous chemistry to your facepiece materials and the permeation effect of smaller molecules squeezing past the larger molecules, vaporous molecules can arrive on the inside of your facepiece and specifically the lens piece. 
The amount to enter your facepiece will be based on the duration of exposure, the ability of the hazardous molecule to fit through the molecular space of the material comprising your facepiece and the concentration of exposure (the more product in a confined area the more likely the permeation may occur).
      Of course, the answer to this predicament relies on the Assigned Protection Factor of your respirator and the use of Level A Chemical Protective Clothing. 
The first concern is what the “Assigned Protection Factor” (APF) is for your respirator.  Each respirator is assigned a specific protection factor (APF) to rate its ability to filter out hazardous vapours and particulate matter. 
The second piece of information we need to know is the exact contaminant that you are dealing with and the concentration level of that material in the environment (usually identified in parts per million - ppm) you are going to be working in. 
You then take the contaminant concentration level (for example 5,000 ppm) and divide it by the APF of your respirator (a typical Positive Pressure SCBA is rated (APF) at 10,000).  The result is the level of exposure that would be affecting you, even with the respirator on and worn correctly.  In this case the exposure would be .5 ppm of the hazardous product.
This may not sound like much but if the maximum permissible exposure is under this amount (and there are plenty of chemistries that are dangerous in less than this concentration) then you will need to wear Level A Fully Encapsulating Chemical Protective Clothing (CPC).  The concept of Level A is to provide a barrier between the hazardous environment and your skin as well as your respirator. 
Permeation occurs also with CPC, but the concentration that makes it through the CPC is very little and therefore your APF of your respirator is adequate to protect you from inhalation injuries.  CPC also has time restrictions of use based on concentration of the product as your skin must be protected from the maximum exposure to absorption issues. 
Remember that there are also different types of CPC based on the core material that the suit is constructed from, or if it is suit made of layers of different materials, and then it is based on the thickness and type of each layer.  You must select the appropriate type of Level A CPC to make sure that you are properly protected from the hazardous materials involved.
You never know what you might meet
In a firefighting situation it is rather unusual to know explicitly what the exact chemistries are in the smoke and fire scene environment air, as well as the exact concentration of these vapours.  The Positive Pressure SCBA respirator has the highest APF of all the various types of respirators and it works in Oxygen deficient and high temperature environments.  Many respirators cannot function in these  two types of environments. So, the fire service traditionally uses the PPSCBA on all responses. 
However, due to permeation, it can be compromised and firefighters should be aware of this and realize that the PPSCBA is not infallible.  Minimal exposure times typically save most firefighters from the lack of awareness regarding what the vapours are actually doing to their respirators, but it certainly is recommended that the responding departments evaluate the air for the presence of contaminants and then evaluate their concentrations and apply the rules for respirator safety as applicable.
In conclusion
One last point is be sure to properly decontaminate your respiratory gear and all your other protective equipment as well.  Decontamination procedures vary based on the chemistries involved and the types of equipment you are wearing at the scene. 
Make sure you refer to the manufacturers specifications when determining how to decontaminate your equipment.  Some decon procedures can be destructive if applied incorrectly or to the wrong types of materials, so check it out first and before you need to perform this important function.
I hope this answer your question and that you seek out the manufacturer’s information for your respirator and protective clothing to ensure you know what the APF is and which chemistries your CPC is capable of protecting you from when operating at emergency scenes.

KEVIN MELLOTT

  • Operation Florian

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