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Static Fire Stories Articles & Technical Papers Current News

A Brief Review of ANSI Z41-1999
"Personal Protection-Protective Footwear"
by: Steve Fowler, Fowler Associates, Inc.

sfowler@sfowler.com............... http://www.sfowler.com

I have been asked several questions about the relatively new standard for protective footwear ANSI Z41. Maybe this article can help answer some of the more common questions.


As reference, the ESD Association has in place three test methods for footwear (including persons & flooring):
ESD S9.1 - Footwear - Resistive Characteristics
ESD S97.1
- Resistance Measurement in Combination with a person
ESD S97.1 - Voltage Measurement on a Person

These test methods have set no limits for the results. However, the new ESD S20.20 document has begun to establish standards for all areas of ESD protection including footwear. The thinking at this time according to the standard is that an ESD protective footwear would have a maximum resistance in conjunction with the floor and person of 35 Meg Ohms. There is currently no work in the ESD Association to classify footwear beyond this resistance limit. There is one more limitation in the use of ESD protective footwear in S 20.20. This is that the voltage measured on a person using the footwear on a designated floor should have a maximum value of 100 Volts.


ANSI Z41-1999 covers footwear which provides protection in the following areas:

1. Toe Guard Footwear
2. Metatarsal Guard Footwear
3. Electrostatic Dissipative
4. Conductive Footwear
5. Electrical Hazard Footwear
6. Soil Puncture Resistant Footwear

In this article I will give a brief overview of the standard specifically in how it relates to Conductive and Static Dissipative footwear.


Conductive Footwear (0 - 500,000 Ohms)

Conductive footwear is defined by ANSI Z41-1999 as any unworn footwear having a resistance of zero (0) to five hundred thousand (500,000) Ohms as measured by the circuit shown below.

The main points to note in this section of the standard are that

1. The footwear is to "unworn" when tested.
2. The voltage is to be 500 Volts.
3. The probe is 2.5 inches in diameter and is all metal.
4. The resistance of this type footwear is between 0 and 500,000 Ohms.
5. There are no sub-classifications of conductive footwear in this standard after 1999.


Static Dissipative Footwear
SD Type I = to

SD Type II =to

Static dissipative footwear is defined by ANSI Z41-1999 as any footwear when tested while being worn by a person and having a resistance from the person's hand to a ground plane of one MegOhm to 1000 MegOhms. The measurement circuit is shown below.

The main points to note in this section of the standard are that

1. The footwear is to be worn by a person when tested.
2. The voltage is to be 50 Volts.
3. The measurement is between the person's hand and a ground plane.
4. The resistance of this type footwear is between 1 MegOhm and 1000 MegOhms.
5. There are two sub-classifications of Static Dissipative footwear in this standard after 1999.
6. The measurement circuit calls for an unspecified current limit of the power supply.

 

The main differences between ANSI Z41-1999 and the ESD Association's Test Methods and Standards are as follows:

1. In Z41, Conductive footwear is tested at 500 Volts with a 5 lb. metal probe only. This is similar to ESD S9.1 which uses a shot filled sock in the shoe on an aluminum insert and measured at 100 Volts.

1. In Z41, Static dissipative footwear is tested in combination with the person on a grounded plane at 50 Volts. This is similar to ESD S97.1 which tests the resistance of the combination of the person, footwear and floor. .

Interesting Point: How does Z41 define a 750,000 Ohms shoe ??????????

 

 

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