¹ EN 14325:2004 - Protective clothing against chemicals. Test methods and performance classiﬁ cation of chemical protective clothing materials, seams, joins and assemblages. ² EN ISO 6529:2013 - Protective clothing. Protection against chemicals. Determination of resistance of protective clothing materials to permeation by liquids and gases.
BARRIER BREAKTHROUGH The barrier or stopping properties of a fabric are measured in terms of breakthrough time ; the time taken for a chemical or hazardous substance to penetrate completely through a fabric.
ANNEXE 4: FABRIC TESTING
Breakthrough time alone is not sufﬁ cient to determine how long a garment may be worn once it has been exposed to contamination. Safe user weartime may be longer or shorter than the breakthrough time depending on the permeation behaviour of the substance, its toxicity and the exposure conditions. In case of mixtures, permeation is measured for the
most toxic substance since permeation cannot be measured for chemical mixtures. Account must be taken of the fact the permeation characteristics of mixtures can often deviate considerably from the behaviour of the individual chemicals. Furthermore, permeation rates are temperature dependent and typically increase with a temperature rise.
NORMALISED BREAKTHROUGH TIME
The classiﬁ cation of permeation data as deﬁ ned by EN 143251 is based upon the normalised breakthrough time measured according to EN ISO 65292 at 1.0 μg/cm2/min.
Normalised breakthrough time is the average elapsed time between initial contact of the substance with the outer surface of the protective clothing material and the time at which the substance is detected at the inside surface at a deﬁ ned permeation rate. The breakthrough time is normalised as it is independent of the sensitivity of the measuring device. A normalised breakthrough time of >8 hours means that the average permeation rate has never reached the rate deﬁ ned according to EN ISO 6529 (0.1 μg/cm2/min or 1.0 μg/cm2/min). However, the substance may have actually broken through.
Table 9. Normalized breakthrough time and EN Class.
Normalized breakthrough time at a permeation rate of 1.0 μg/cm²/min in minutes
> 10 1
> 30 2
> 60 3 > 120 4 > 240 5 > 480 6
* EN 14325: Protective clothing against chemicals test methods and performance classiﬁ cation of chemical protective clothing
Actual breakthrough time is the average time elapsed between initial contact of the chemical or hazardous substance with the outer surface of the clothing material and the detection of the chemical on the inner surface by a measuring device.
A permeation rate of ND (not detected) does not necessarily mean that breakthrough cannot occur or has not occurred. It simply means that permeation was not detected after the test observation time of eight hours. Permeation may indeed have taken place, but at less than the minimum detectable permeation rate (MDPR) of the measuring device. MDPR can vary depending on the sensitivity of the analytical device for the given substance.