This is the first of a three-part article on bunker gear materials, design and selection. In A we will consider factors that determine the criteria for bunker gear selection. We will then discuss the characteristics of the most widely used bunker gear outer shell fabrics. In Parts B and C we will discuss moisture barrier and thermal barrier materials, and the care and maintenance of your bunker gear. The selection of modern bunker gear involves three factors:

• recognizing and defining the fire fighting environment in which your firefighters function (Fire Fighting Environment);
• the performance requirements of the bunker gear materials that are defined by your fire fighting environment, (Materials Performance Requirements) and;
• the garment design which is most compatible with the fire fighting environment and the required bunker gear materials (Garment Design Criteria).

Fire Fighting Environment

The nature of fire fighting and fire fighting injuries has changed substantially over the years. Major departments are consistently reporting that less than 2% of calls involve structural fires. Concurrently, vehicle extrication and EMS calls are steadily increasing.

As well, the NFPA statistics on firefighter fatalities show that stress is the leading cause of death.

These two facts -- the low percentage of calls involving structural fires and the high percentage of firefighter deaths and injury resulting from stress -- suggest that fire departments should be focusing attention on stress reduction, in other words, on increasing firefighter mobility and comfort.

It is therefore important for the department preparing to purchase new bunker gear to first perform a diagnostic of the environment in which its firefighters work. Such a diagnostic should consider the following:

• the number of calls made per year
• the percentage of calls that involve structural fires
• the percentage of calls that are EMS related
• the percentage of calls that involve vehicle extrication
• the distribution of calls between summer and winter
• the local climate (e.g. temperate & wet, cold or hot & dry, etc.)
• the department's fire attack procedures
• the physical conditioning and age of its firefighters

Materials Performance Requirements

The department should then define the performance requirements of the materials it wants in its bunker gear in relation to the environmental diagnostic. These requirements can be grouped as follows:

1. hose requirements affecting garment life:
   • Tear and abrasion resistance
   • Resistance to UV degradation (strength and appearance)
   • Ability to be reused after exposure to high temperatures (thermal damage tolerance)
   • Resistance to molten metal splatter or burning embers
   • Cleanability

• Ice-shedding ability
• Water absorption on the fire ground
• Weight and suppleness Increased mobility (this is a function of both materials and design)
• Visibility
• Thermal protective performance (TPP) of all the layers together in the garment
• Breathability of the moisture barrier

It is important to remember that there is often a trade-off between the different performance requirements or characteristic; for example, the fabric with the best thermal damage tolerance may have relatively poor UV degradation performance. And there is always a trade-off between price and performance: the higher the performance, the higher the cost.

Garment Design Criteria

Garment design is no less important than the fabrics that go into bunker gear. And like the materials performance requirements, the garment design requirements or criteria flow from the needs of the particular fire department's environment.

The criteria the fire service should consider in evaluating the design of any bunker gear include:

• comfort and fit
• lightness
• mobility
• protection
• availability of extra features

And one of the most important things to remember about bunker gear is that it is a three-layer system consisting of an outer shell, a moisture barrier and a thermal barrier. It is these three layers working together that determine the comfort and the protection the gear will offer.

PART A Outer Shell Fabrics

The outer shell is the first line of defense for the firefighter. It provides flame resistance, thermal resistance, and mechanical resistance (to cuts, snags, tears, and abrasion). There is a variety of outer shell fabrics available with different advantages and disadvantages. The following summary gives a brief overview of the most commonly used fabrics. To avoid accusations of bias we've listed no disadvantages for any of the fabrics.. However, test results from independent laboratories and the experience of user departments can be obtained to help in the evaluation of any outer shell fabric.

NOMEX IIIA® 7.5 oz

Characteristics

Weight 7.5 oz/yd²
Plain weave blend of Nomex (93%), Kevlar (5%), and carbon fiber (2%)
Low price
Wide choice of colors
Good tear and abrasion resistance
Good price performance/ratio

ADVANCE^TM

Characteristics

Weight 7.0 oz/yd²
Ripstop weave of Kevlar (60%) and Nomex (40%)
Priced between Nomex and Kevlar/PBI
Good tear and abrasion resistance
Better thermal damage tolerance than Nomex
Good TPP-to-weight ratio

DELTA T®

Characteristics

Weight 7.0 oz/yd²
Twill weave of Nomex (75%) and Kevlar (25%)
Supple and soft
Higher thermal damage tolerance than Nomex IIIA
Priced between Nomex and Kevlar/PBI

KEVLAR/PBI

Characteristics

Weight 6.2 or 7.5 oz/yd²
Ripstop weave of Kevlar (60%) and PBI (40%)
High thermal damage tolerance, i.e. high char temperature and remains flexible after charring
Highest priced outer shell fabric

DURALITE^TM

Characteristics

Weight 6.0 oz/yd²
Twill weave of multi-filament Kevlar (50%), multi-filament Nomex (25%) and spun Nomex (25%)
Very high tear and tensile strength both new and after UV exposure and after washing
Lightweight
Slippery and supple
Thermal damage tolerance between Nomex and Kevlar/PBI
Excellent ice shedding properties
Cleans up more easily than some other fabrics
High TPP-to-weight ratio
Price close to that of Kevlar/PBI

N.B. Duralite is made up predominantly of filament yarns whereas all the other outer shell fabrics are made up of spun yarns (filament yarns are to spun yarns as fishing lining is to sewing thread). The advantages of multi-filament fabrics are an exceptionally high strength-to-weight ratio and very low coefficients of sliding and static friction (i.e. increased mobility) compared to spun yarn fabrics.

Z200^TM

Z200 is the exclusive outer shell of DuPont's Nomex Omega® Turnout System.

Characteristics

Weighs 7.5 oz/yd²
Good thermal damage tolerance Very high TPP-to-weight ratio
Soft and supple
Good resistance to color fading

BASOFIL®

This is a new fiber from BASF and chemically is essentially the same as melamine®.

Characteristics

Weighs 7.5 oz/yd
Ripstop weave of Kevlar (60%) and Basofil (40%)
Mechanical strength characteristics similar to Kevlar/PBI
Good thermal damage tolerance.
Very high TPP-to-weight ratio
Available only in natural (straw yellow) or tan colors.

What is the Best Outer Shell Fabric?

One often hears this question and the answer too often depends on who is selling the fabric or the bunker gear rather than on the facts. The best outer shell fabric depends on the individual fire departments needs. For example, if a fire department has a tight budget but wants gear that is durable and will provide good protection, then the "best" outer shell fabric may be 7.5 oz/yd² Nomex. If a fire department's concern is maximizing firefighter comfort, durability and protection then Duralite may be considered to be the "best" fabric. And if a fire department's principal concern is to be able to repeatedly expose its bunker gear to temperatures in excess of 1000 °F. and have fewer replacements or repairs of burned outer shells then Kevlar/PBI may be the "best" choice.

The Choice of Outer Shell Fabric vs. Thermal Protection

There is, however, one misconception that should be recognized and dispelled. That is the widely held belief that the type of outer shell fabric is the critical factor in determining whether or not a fire fighter is injured during flashover conditions. More specifically, it is often believed that Kevlar/PBI provides better burn protection than other fabrics.

However, the TPP test has always shown that Kevlar/PBI provides no more thermal protection than any other fabric of an equivalent weight. In fact, repeated testing on thermal mannequins at North Carolina State University and at DuPont's facility in Wilmington Delaware has shown that all the currently approved outer shell fabrics provide approximately the same degree of protection in flashover conditions. In fact, these mannequin tests revealed that after a 12 second exposure to flashover conditions-- after which the reflective tape was completely burned off the gear, the outer shell was crisped and broke open (even Kevlar/PBI) -- there were less than 5% second degree or third degree body burns registered by the sensors on the mannequin, irrespective of the outer shell fabric on the garment.

And as for protection from burns in less than flashover conditions, e.g. from compression burns, testing being done on the behalf of NFPA for the 2000 revision of NFPA 1971 and by the 3M corporation has shown that the type of moisture barrier and the water absorption characteristics of the different layers of the garment, not the type of outer shell fabric, are the critical factors influencing the likelihood of burn injury.

Conclusion

There is no simple answer to bunker gear selection. Your selection of materials and design will be determined by the unique operating environment of your department. The selection of the outer shell fabric for your bunker gear is a compromise between many competing factors: cost, comfort, protection, durability, etc. Go beyond the salesman's hype to select the outer shell that best meets your needs and constraints.

More information...

B. About Moisture Barriers In Turnout Gear
C. About Thermal Liners

• NOMEX, KEVLAR, NOMEX OMEGA TURNOUT SYSTEM, Z200 and DELTA T are trademarks of E. I. DuPont
• ADVANCE is a trademark of Southern Mills
• DURALITE is a trademark of Securitex Inc.
• Basofil is a registered trademark of BASF AG