The merino wool that we use has many unique performance properties and here we look at the fibre's naturally occurring flame resistance (FR). This natural FR is generating interest as we are hearing more and more about the importance of fire fighter well being with growing concerns about clothing toxins. Added to this uncertainty is that to make some textiles flame resistant they are treated with a number of chemicals and should these chemically treated textiles be exposed to heat or flames they can produce hazardous gases (known as off-gassing) which may be inhaled by the wearer. With these facts in mind the naturally occurring fire resistance of the Armadillo Merino® wool looks more and more attractive.
Why is Armadillo Merino® Naturally Flame Resistant?
This flame retardant properties are due to its unique chemical structure (a high nitrogen content (14%) combined with a high relative moisture content), which displays the following beneficial properties:
- A very high ignition temperature (570-600°C)
- Doesn’t melt or stick upon burning, rather, it forms an insulating char
- Self extinguishing
- A high Limiting Oxygen Index (20- 25%) – with the LOI being a measure of the minimum % of oxygen required to sustain combustion
- A low heat of combustion
- A low rate of heat release
- Evolution of less smoke and toxic gases than formed during combustion of most synthetic fibres
What does this mean?
Wool requires higher levels of oxygen in the surrounding environment in order to burn. Wool may ignite if exposed to naked flame but it wont support the flame and will instead smoulder – usually for a short time. Take the flame away and it goes out (self extinguishing). In addition, wool’s cross-linked cell membrane structure will swell when heated to the point of combustion forming an insulating layer that prevents the spread of flame. This also means that wool produces less smoke and no toxic gas unlike synthetic fibres.
Of the commonly used textile fibres (cotton, rayon, polyester, acrylic and nylon), wool is widely recognised as the most flame resistant, as can be seen in the summary below.
The flame resistance key points for Armadillo Merino® are:
- Naturally flame resistant, and its performance exceeds that of all other commonly encountered textile fibres.
- Has a low heat of combustion and a low rate of heat release.
- If it comes into direct contact with another burning surface it won’t melt or stick.
- Is self extinguishing once the initial ignition source is removed.
- If it does burn it forms an insulating char. When the fibre burns it generates less smoke and toxic gases compared to the combustion of most synthetic fibres
In conclusion, we believe there is no place for chemically treated flame resistant base layers in the first responder environment especially when there is a superior natural solution available. Often the user is unaware until it is too late of the extreme danger they are exposing themselves to when wearing a “wicking” synthetic base layer.
When you consider all of the above, the case just keeps getting stronger for merino wool as the safest option for first responders next-to-skin clothing and as their last line of defence.
If you are interested in more, see "Is it time that Police consider the base layer as their last line of defense".