Fire Suit Outer Fabric Material
All the fibres used in the construction of a fire Suits would be fire resistant and are composites of either PBI, PBO, Nomex, Kermel, Conex, Twaron , Kevlar or alternative unbranded fibres. All these fibres make claims of what they do well, if the outer fabric was constructed of 100% singular fibre they would not be suitable for use, as they all have their positive and negative aspects. The three common materials we use i in our suits are:
Nomex
Nomex used to be and still is in some countries the main outer fabric used in the construction of fire suits due to its lower cost, versatility in the variety of colours the yarns can be supplied in, good colour and lightfastness and in the handle of the of the fabric itself. The downside of the fabric is unless the Nomex is blended with a high concentration of para-aramid the fabric will break open after a flash over. The very nature of the flashover causes Nomex fibre to carbonise making it brittle after the flame/heat has been removed causing the fabric to crack of break open. One of the latest developments from Nomex to counteract this break open is Nomex 360, which is a fabric blend of Nomex, filament Kevlar and PBO. This is an exceptionally strong fabric due to the increased percentage of Para aramid and PBO blended.
Kevlar
Compared on a strength-to-weight ratio, Kevlar is about 5–6 times stronger than steel wire and twice as strong as ordinary nylon fibre. … Unlike its sister material, Nomex, Kevlar can be ignited but burning usually stops when the heat source is removed.
Kevlar® filament is engineered into premium fabrics to help reduce fabric profile while strengthening fabrics to new levels of performance.
The Kevlar filament will provide excellent thermal stability; equal to or better than Nomex. And the tensile strength of Kevlar filament is four times that of Nomex. Kevlar is a great fibre for both strength and fire resistance; unfortunately, it is not for moisture management.
Kevlar® is very strong and is slightly stronger than Carbon Fibre per unit weight. … Aramid fibre exhibits similar tensile strength to glass fibre, but can be twice as stiff. It is a light, polyacrylamide plastic fabric, which has a high tensile strength. this means it takes a huge amount of energy to make its fibres stretch even a little. The disadvantages of Kevlar are the ability to absorb moisture, difficulties in cutting, and low compressive strength.
PBO
Is a high-performance, heat-resistant fibre with a benzene-fused oxazole ring structure. The fibre is almost twice as strong as aramid fibres (Kevlar, Nomex) and about 10 times stronger than steel making it the strongest manmade organic fibre Probably one of the strongest fibres in the world but like PBI has its weaknesses, the main one being that when its subjected to UV light it degrades and weakens. But since the fibre is traditionally blended with Para aramids like Kevlar even after exposure to UV light the fabric will still give a good tear and tensile strengths values more than those required by the fire standards. Then benefits of PBO blends are that the fabric gives exceptional strength retention after exposure to heat and flame without break open coupled with the claimed exceptional breathability which would reduce heat stress.
