Written by: <Authors><Author><Id>185</Id><Name>Hireni Mankodi</Name><FriendlyName>hireni-mankodi</FriendlyName></Author><Author><Id>185</Id><Name>Hireni Mankodi</Name><FriendlyName>hireni-mankodi</FriendlyName></Author></Authors>
Written by: <Authors><Author><Id>185</Id><Name>Hireni Mankodi</Name><FriendlyName>hireni-mankodi</FriendlyName></Author><Author><Id>185</Id><Name>Hireni Mankodi</Name><FriendlyName>hireni-mankodi</FriendlyName></Author></Authors>
"Jerry McGee is an Oklahoma pipeline field foreman. Onwhat started out as a routine workday, Jerry set off alone to inspect abroken-down pump motor. The motor's fuse had blown and had caused the uppersection of the starter-motor to burn. In need of a fire extinguisher, Jerry proceeded to shut the cabinet door. As he did so an arc flashed out, blowing the door open andknocking Jerry clear across the building. Jerry received second and thirddegree burns to his hands and the face, but coverall he was wearing prevented injuries to other parts of the body, including his wrists, which were covered by theoveralls cuffs. Had he been wearing standard apparel which cant easilyignite, Jerrys story may have been very different."
"Engineered Garments"
Thirty years ago, scientists from E.I. DuPont de Nemours andCompany created fibers for firefighter's protective clothing known as Nomex andKevlar. The aramids inherent flame-resistant properties make it ideal for themanufacture of fireproof clothing. Kevlar is a para-aramid organic fiberconsisting of long highly oriented molecular chains produce frompoly-paraphenylene terephthalamide (DuPont). The highly oriented chains withstrong inter-chain bonding which result in a unique combination of properties, including: high tensile strength at low weight, low elongation to break highmodulus, low electrical conductivity, high chemical resistance, low thermalshrinkage, high toughness, excellent dimensional stability, high cutresistance, flame resistance and self-extinguishing.
The Need of Protection
Protections from heat, flame, molten-metal splashes, severecold and frost, radiation source, etc. are prime requirement for both civil anddefense applications. There are various risks, which require proper protectionof the human body in order to minimize the damage, both at physiological andpsychological level. Thermal risks in fire situations against which human skinhas to be protected may be due to:
Human tissue is very sensitive to temperature. When humantissue is exposed to any of the above hazards, the body experiences pain/second-degree/ third degree burn. Total heat energy as low as 0.64 cal/cm2(26.8 kJ/m2), results in a sensation of pain, and 1.2 cal/cm2(50.2 kJ/m2) causes second-degree burns on exposed tissues. At 45 0C,the sensation of pain is experienced, and at 72 0C the skin iscompletely burnt. The mode of transfer establishes the means by which protection should be achieved. The rate of heat transfer is measured in terms of heat flux,which is the quantity of heat passing through unit area per second; it is expressed in kW/m2. The measured heat flux determines the level of protection required. In order to achieve thermal protection the protective fabric/ clothingshould meet the following requirements.
Combustion and Prevention Mechanism of Fiber:
The effect of heat on a fibre can produce a physical as well as a chemical change. In order to understand the protective function of the fabric and the garment, it is essential to understand the combustion mechanism of the fibre. A preventive step can be decided only after understanding the mechanism of combustion of fibre.
Textile combustion is a complex phenomenon that involves heating, decomposition leading to gasification, ignition, and flame propagation. The rate of the initial rises in temperature depends on the fiber specific heat, thermal conductivity, latent heat of fusion, vaporization or other enthalpy changes that occur during the combustion. In thermoplastic fibers, the physical changes are at second-order transition and subsequently melting occurs at a melting temperature, whereas chemical changes take place at temperature where thermal degradation (pyrolysis) occurs and the temperature where subsequent oxidation and combustion may occur. The Different thermal propertied of different fiber listed in Table 1. Fibers undergo combustion when exposed to heat either directly or via the route of pyrolysis (Tp)-oxidation-combustion (Tc) as indicated in the Fig 1.
Table 1 Thermal Transition Temperatures of Fibers:
Fibre |
Tg (0C) (Softens) |
Tm (0C) (Melts) |
Tp (0C) (Pyrolysis) |
Tc (0C) (Combustion) |
DH (kJ/g) |
|
Wool |
- |
- |
245 |
600 |
27 |
25.0 |
Cotton |
- |
- |
350 |
350 |
19 |
18.4 |
Viscose |
- |
- |
350 |
420 |
19 |
18.9 |
Triacetate |
172 |
290 |
305 |
540 |
- |
18.4 |
Nylon 6 |
50 |
215 |
431 |
450 |
39 |
20.0-21.5 |
Nylon 6.6 |
50 |
265 |
403 |
530 |
32 |
20-21 |
Polyester |
80-90 |
255 |
420-477 |
480 |
24 |
20-21.5 |
Acrylic |
100 |
>220 |
290 |
>250 |
32 |
18.2 |
Polypropylene |
-20 |
165 |
469 |
550 |
44 |
18.6 |
Modacrylic |
<80 |
>240 |
273 |
690 |
- |
29-30 |
PVC |
<80 |
>180 |
>180 |
450 |
21 |
37-39 |
PVDC |
-17 |
180-210 |
>220 |
532 |
11 |
60.0 |
PTFE |
126 |
>327 |
400 |
560 |
4 |
95.0 |
Oxidized acrylic |
>640 |
- |
55 |
- |
- |
- |
Nomex |
275 |
375 |
310 |
500 |
30 |
28.5-30 |
Kevlar |
340 |
560 |
590 |
>550 |
- |
29 |
PBI |
>400 |
- |
>500 |
>500 |
- |
40-42 |
* LOI: Limiting-oxygen index.
Four ways of prevention of combustion have been suggested as follows:
The Effect of Fiber / Fabric Construction:
The flame resistance / retardance of the textile material depends on the fibre nature, fabric/yarns structure and fabric composition. The nature of the fibre decides its inherent tendency and ease of burning whereas fabric composition shows different type of such constituents and gives an indication of the burning behavior. The structure of yarn and fabric decides the rate of burning and fabric construction, with the fabric weight plays an important an important role in deciding the suitability for different work wear applications as listed below.
Performance Garment for Fire Fighter:
The primary goal of any performance garment system is to eliminate/ minimize the risk due to hostile environment, regardless of the location. In case of fire fighting, the immediate reflex action is to control an emergency as quickly as possible and at the same time take steps to minimize eventual damage to and loss of materials and persons. The objectives of a fire fighter reaching an incident are to:
The role of the fire fighters' personal protective clothing is not only to protect the fire fighter but also to enable the fire fighter to achieve above mentioned objectives. The type of protective garments and the protection it offers are selected on the basis on the degree of risk involved; fire-fighting protective garments are classified as:
Fig 2 shows garments are used at different levels and in different applications depending upon the modes of heat transfer and hazards involved in combating the hostile environment.
Fig 2: Fire-fighting protective garments
Protective Garments for structural Fire Fighter:
The activities of rescue, fire suppression, and property conservation in buildings, enclosed structures, vehicles, and vessels or like properties that are involved in a fire or emergency situation are termed as Structural Fire Fighting. Various municipal fire brigades require protective clothing for fire fighting.
Fig 3.Conventional Fire Fighter Suit
All protective garments for structural fire-fighting operations must meet the garment element requirements of NFPA 1971 in North America and EN 469 in European Union. Protective garments are the coat (standard length-35"), trouser (standard length-26", 28", 30", 32"), or coverall elements of the protective ensemble that are designed to provide minimum protection to the upper and lower torso, arms and legs excluding the head, hands and feet.
Protective coats and trousers consists of a composite of three functional layers:
Table 2 - Material use for different functional layers:
Functional Layer |
Material Options |
Outer Shell The outer shell is a flame and heat resistant barrier that provides a first line of defence against the external environment and protects the moisture barrier and thermal barrier from physical damage. |
|
Moisture Barrier The moisture barrier is that garment layer used to prevent the transfer of water from the outside environment to the fire fighter's body |
|
Thermal Barrier The thermal barrier is that layer of the garment that separates the moisture barrier from the body and provides insulation from heat. |
|
Fabrics and other components utilized by the manufacturer are generally obtained from the same sources. Finished garments differ due to the type of components chosen as well as other factors such as fit, which is directly related to the quality of the manufacturer's design, patterns and care in construction techniques (i.e. cutting, sewing and seam finishing). Some of the small important parameter of garment parts needs to design very carefully along with other aspect to get proper functionality on work field. Some of components are list below.
Firefighter Stress Matrix
Ergonomic is the important aspect need to consider especially in performance garment. On action field lots of body movement takes place, which puts lots of stress on body if garment is not properly design. For designing firefighter suit the mechanism of heat stress can be understood by considering following points.
i.Vapor transmission
ii.Ventilation
iii.Clothing absorption
This implies that there are several design goals to pursue in developing minimally stressful clothing. These are:
Selection of Design:
The selection of the design was based on the feedback of the fire services like Ahmedabad Fire Brigades, Delhi Fire Service in India. The requirement was for a garment, which satisfied the design goals as mentioned above besides being cost effective. According to the station officers at the respective fire services:
Based on the above-mentioned considerations a prototype design for coverall was conceived which would improve the overall functionality of the garment by optimizing the above mentioned design goals.
The Prototype Design for Coverall:
A coverall was chosen for fire fighting operations because of the following unique features associated with a coverall, which improves its functionality. Fig 4 shows prototype design of coverall
Lighter: A coverall reduces the garment weight considerably thereby facilitates working for longer hours with lesser fatigue. A weight reduction of 25% is achievable when compared with average turn out coat & pant combination on account of no coat/ pant overlap and lesser fasteners.
Faster: The turnout is faster to dress-up being a single piece garment.
Breathability: The design creates an air jacket between the skin ant the garment shell which facilitates ventilation and hence the overall comfort of the garment.
Slimmer: The slender profile helps to get in (and out) with ease. The possibility of occasional "stuck up" of the coat with the protruding objects during fire fighting operations; is minimized.
The prototype design can be used for various options of outer shell (in this case only one), moisture barrier & thermal barrier, depending on the need. The following options were exercised for the manufacturing of the coverall Table 3:
Table 3: Specification for Coverall:
Component(s)/ material(s) |
Specifications/ Features |
1. Fabric (Outer shell only) |
Denim (14.5 oz./yd2): Offers excellent insulation, absorption, and skin-friendly properties. |
2. Front Zipper |
Two-way zipper for improved functionality. |
3. Hook & Pile fasteners |
At cuffs, ankles, waist-band, throat tab, storm flap. |
4.Retro-reflectiveTrims (optional) |
At front & back at trunk level, arms, legs. Options: ScotchliteTM & ReflexiteTM |
5. Collar |
Denim with stand-up and lay-down comfort. |
6. Pockets |
Patch pocket at front. |
7. Cuffs |
With hook & pile fasteners at wrist and ankles. |
8. Reinforcement |
Leather, at elbows and knees. |
9. Color |
Lime orange for excellent daytime visibility |
10.Gusset |
At armholes and crotch. |
11.Thumbhole |
For preventing exposure of wrist. |
12. Size |
Medium |
Fig 4 Prototype of Design for Coverall
Functional Features of Coverall:
Various functional features have been incorporated in the garment are:
The prototype design is for low risk fighting operations only and not for specialized fire fighting like proximity fire fighting, fire entry etc. however, the design and the functional features can be adapted with different combinations of the materials (fabric) so as to be suitable for specialized fire fighting operations.
References
About the Authors:
Dr. Hireni Mankodi is the Sr. Lecturer, Textile Engineering Department, Faculty of Technology and Engineering Kalabhavan, Baroda and Mr. Mehul Pancholi is the Manager Production, Arvind Mills, Ahmedabad.