As we know heat from an electric arc is an important hazard that workers need to be protected from. Once end users have carried out their own risk assessment and if they have identified as a result of this to provide their workforce with FR protective clothing, there are new standards and test methods that they can refer to

Clothing is subject to draft norm IEC 61482-2. In order to choose adequate protective clothing, the potential incident heat energy (in units of energy per square surface) caused by an electric arc and to which a worker may be exposed, needs to be calculated in this thorough risk assessment.

Within the garment standard, the norm refers to fabrics that can be tested to "open arc", covered by by IEC 61482-1-1 (now EN 61482-1-1) or "arc in a box" covered by IEC 61482-1-2 / EN 61482-1-2

Quantifying the arc rating of a protective garment
1. The arc rating is most commonly quantified by the ARC THERMAL PERFORMANCE VALUE (ATPV) determined by the open arc test method EN 61482-1-1. The ATPV represents the maximum incident thermal energy in units of energy per surface area (e.g. kJ/m2 or cal/cm2) that a fabric can support before the wearer will suffer 2nd degree burns.

The break-open threshold energy (or EBT) is another fabric characteristic. It represents the highest incident energy exposure value on a fabric where the garments do not exhibit break-open. The formation of holes in the fabric caused by break-open would allow heat or flames to pass through. Workers are assumed safe if the arc rating of their clothing (or ATPV value) exceeds the electric arc incident energy as calculated in the worst case scenario of a risk assessment.

NOTE: IEC and EN 61482-1-1 are equivalent to the American Standard Test Method ASTM F 1959M)

2. The box test is another way to measure the protective performance of clothing against the thermal effects of an electric arc and is defined in the IEC 61482-1-2 / EN 61482-1-2 test method. In this test, the fabric is exposed to an electric arc confined in a specific box with a specific electrode arrangement.
Class 1
Arc Duration= 0.5s Arc Current = 4kA
Class 2
Arc Duration= 0.5s Arc Current = 7kA

A fabric passes the test:
- if the heat transferred behind the fabric does not cause second degree burn (i.e. is below the Stoll curve)
- if the after flame time is below 5 seconds
- if there is no melting to the inner side of the fabric
- if a hole caused by the arc is not larger than 5 mm in every direction (in the inner most layer).

Test conditions for Class 1 try to simulate typical exposure conditions for a short circuit current of 4 kA protected by devises limited the duration of the arc to 0.5 seconds in confined space, and of 7 kA respectively for Class 2.

(To be used in Low Voltage Systems only)

DuPont TM Arc-Man(r)
This equipment developed by DuPont measures the ATPV value of protective fabrics and garments in simulated open electric arc incidents. This is configurated to IEC/EN 61482-1-1.

Incident energy is calculated on several parameters influencing an electric arc, such as current, duration of the arc, electrode material, the gap between the electrodes and the distance of the tested fabrics or garments to the arc.

Arc-Man(r) can test fabrics on panels, measuring the ATPV value of the fabric system (in cal/cm2) so that it can be compared with the incident energy calculated in the end user's risk assessment. Arc-Man(r) can also perform complementary garment tests on a torso to show the effect of a garment's design and integrity of manufacture, allowing an assessment of the garment's behaviour (e.g. of the closure system, the pockets, etc.).

ARC-MAN(r) IS SIMILAR TO KINECTRICS TEST FACILITY

Recommendations

- DuPont recommends that all layers are made of inherently flame resistant materials
- inappropriate underwear could ignite or melt, thus having an adverse effect on protection aggravating the outcome of an electric arc incident
- Nomex(r) offers single layer and multi-layer protective clothing solutions against electric arc hazards, conforming to IEC 61482-2 when tested according to IEC 61482-1 / EN 61482-1-1 (Open arc incidents) and IEC 61482-1-2 / EN 61482-1-2 (Arc in a Box or confined arc incidents).

Electric arc protective clothing can receive IEC 61482-2 certification if one of the following requirements are met:
- the ATPV value of the clothing must be at least 4 cal/cm2
- the clothing has to pass at least the electric arc box Class 1.

DuPont recommends to the user to ask weavers and garment manufacturers for an offering of fabrics, fabric systems and garments, which meet his or her specific arc rating needs and also his needs of other important properties in the best combination. Our NQP weavers, knitters and garment manufacturers can provide you with tested and certified solutions.

A great website giving much more detail and a contact of where you will be able to purchase garments is

[url='http://www.arcflashprotection.co.uk']www.arcflashprotection.co.uk[/url]

Some Contacts at Partner Weavers

Estambril
Jordi Querol
Tel: +34 93 748 4545
Fax: +34 93 7274430

E-Mail: j.[email='<[email protected]'][email protected][/email]
[url='http://www.estambril.com']www.estambril.com[/url]


Fuchshuber (Knitter)
Jörg Vois
Tel.: +49 (0)7129/6915-20
Fax: +49 (0)7129/6915-15
Email: [email protected]


Ibena
Britta Smeulders - Technical Manager
Tel: +49/(0)2871/287-131
FAX: +49/(0)2871/287-130
Mobil: +49/(0)174/3426021
E-Mail: [email protected]

Sofileta
Colin Clark
Tel: +44 7827 966599
Email: [email protected]

Garment Manufacturers Providing Arc Clothing

JK Ross
Chris Ross
+44 7802 558995
[url='http://www.arcflashprotection.co.uk']www.arcflashprotection.co.uk[/url]
Email: [email protected]

ROFA BEKLEIDUNGSWERK SCHUTTORF
Attn: Mrs. Silke Kamps
Fabrikstrasse 23
Postfach 1280
48457 Schüttorf
Germany

Tel: 0049 59 23 898 0
Fax: 0049 59 23 898 80

[email protected]

[url='http://www.rofa.de']www.rofa.de[/url]

[/u]ALWIT GmbH[/u]
Attn: Mr. Siegfried Assmann
Kattegatweg 6
46446 Emmerich-Elten
Germany

Tel: 0049 28 28 91 46 23
Fax: 0049 28 28 91 46 46

[email protected]
[url='http://www.alwit.com']www.alwit.com[/url]

FPG ENERGOCONTRAKT
Attn: Mr. Alexander Bolshunov
Business Center “Arabat Fashion House”
Karmanitsky per.9
119002 Moscow
Russia
Tel: 007 095 9371615
Fax: 007 095 9371614
[email protected]

PWG BEDRIJFSVEILIGE KLEDING B.V.
Attn: Mr. T. Sorgedrager
Postbus 103
4460 AC Goes
The Netherlands
Tel: 0031 113 21 34 40
Fax: 0031 113 23 26 75
[email protected]

[url='http://www.pwg.nl']www.pwg.nl[/url]


I'd be delighted to respond to your queries

Hi Elaina,
Sorry for this late reply/question.
I have a doubt about ATPV definitions and this could be a main issue to understand the US / EU differences.
For me, according ASTM/NFPA "[SIZE=1][font=Times-Roman]ATPV is defined in ASTM F[/font][/size][SIZE=1][font=Times-Roman]1959-06 as the incident energy on a material or a multilayer[/font][/size]
system of materials that results in a 50 percent probability that sufficient heat transfer through the tested specimen is predicted to cause the onset of a second degree skin burn injury based on the Stoll curve, cal/cm
[SIZE=1][font=Times-Roman]2[/font][/size]
[SIZE=1][font=Times-Roman]."[/font][/size]


[font=Times-Roman][font=Times-Roman][font=Times-Roman]According your description above (on my understanding) "The ATPV represents the maximum incident thermal energy...".[/font][/font][/font]
[font=Times-Roman][font=Times-Roman][font=Times-Roman]If someone use/adopt for example 95 percent probality is this more safe than 50% probability?[/font][/font][/font]
[font=Times-Roman][font=Times-Roman][font=Times-Roman]Thanks very much,[/font][/font][/font]
[font=Times-Roman][font=Times-Roman][font=Times-Roman]Dagoberto Lara[/font][/font][/font]

Elaina,
You are, of course, very aware of my opinion in that I really have no idea why a user would refer to the box test.
My own experience is that it is not reproducible and on top of which it does not really represent what happens in "real life".
The box test came about because Sweden had an issue with electrical burns - some 200 per annum. Ian McLean of the UK Health & Safety Executive suggested that these statistics would, in the UK, require them to review their work practices.
However, they threatened the Vilamoura Procedure and other EU NC's signed on to develop an "economic" method of evaluating clothing that would not contribute to the injury of a person subjected to an electric arc. The original terms of reference changed as the project developed in Cenelec and the box test was born.
But it is, as you point out, limited in its application.
My own opinion is that a user needs to determine the risk (if it exists at all because there is a lot of paranoia now) and then provide the appropriate and adequate ppe to deal with it not forgetting that the first option must always be to remove the hazard.
Disappointingly, I am seeing workers garbed in "michelin man" suits. Is that really acceptable? I think not.
Cheers,
Tony

If you want to consider the statistical likelihood of a burn occurring at all, you cannot get myopic and look at only ONE factor, the clothing system rating method. You need to look at the complete picture. In almost every realistic scenario, even if the calculated incident energy is the same as the clothing ATPV (a very rare occurrence), the actual probability is far lower than "50%" injury rate. In the vast majority of conditions, workers are overprotected. However from an engineering point of view, what we currently have is a methodology that gives practical and conservative results. I am not aware at this time of any published cases where someone wore the clothing tested via ASTM 1959 or IEC equivalent, based on an incident energy calculation performed using IEEE 1584. Arc flash incidents are pretty rare in the first place, but we've had nearly 10 years of time now to find a "chink in the armor" with none to be found. If anything, this suggests that we are overprotecting using CURRENT standards. If the actual protection was only 50%, then the industrial incident rate would likely be somewhat more than half of what it was 10 years ago (because not everyone is going to follow the recommendations), but so far that has not been the case.

There are several reasons why this is so:
1. The test and the statistics are "pass/fail", not 50%. We are dealing with a binary situation here. Increasing the ratings does not make the clothing somehow "safer". It simply alters the statistics. Wearing less than the recommended clothing may not result in an injury. But it changes the statistical likelihood.
2. The test works on cloth samples placed at a perpendicular position to the arc source. It does not test clothing SYSTEMS. This means that:
A. As humans are not flat objects, much of their bodies is inherently far better protected (incident energy is cosine of the incident angle).
B. Any undergarmants at all tend to drastically increase the ATPV. See [url="http://www.arcwear.com"]www.arcwear.com[/url] for some actual public test data. Even non-AR cotton undershirts give much improved results.
C. Clothing has seams and other parts where again, protection is much greater than a single layer of cloth placed perpendicular to an arc source.
D. The cloth samples are all evaluated as pass/fail and then the data is mathemtically fit to a sigmoidal curve. A careful examination of a few of these curves suggests that the curve slope is far too gradual. Few if any test samples fail more than 0.5 to 1 cal/cm^2 beyond the 50% reported number. The 95% mark is far beyond this value.
3. The clothing test CANNOT be considered in isolation to the environment. The incident energy calculation (for instance IEEE 1584) calculates an average worst case value. Actual arcs are strong affected by for instance the phase angle which in turn affects the assymetrical current during a fault. Plotting incident energy vs. phase angle at a threshold (such as say 8 cal/cm^2) indicates that the incident energy will only be within 0.5 to 1 cal/cm^2 a little over 10% of the time. So you get your "90%" survival rate "for free" statistically in the first place.
4. In practice with large sites (>1000 bus), only a very small fraction of the buses (usually about 5%) fall within a 0.5 to 1 cal/cm^2 "window" of the limits of the clothing in the first place.
5. The working distance is an assumption based on typical equipment and a worst case scenario. Actual measured distances to the area of concern (face and chest area) produce different results than the recommended values in IEEE 1584.
6. The ASSUMED arc is always modeled as the worst case location, on the bus bars in the back of the cabinet, where the highest arcing current will be found. However from a statistical point of view (e.g. IEEE 493), this is NOT very likely to occur at all in practice.