Reply To: THp2 filters for asbestos work

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    Hi Neil,


    I have never heard of these before – we use P3 filters for our respirators. Both half mask and full face (we don’t use hoods).


    However I did have a look at some of the suppliers websites, this morning and afternoon to see if I could be of some help at least.

    Almost all of them say similar things, with regard to the product you have listed (TH2 filter):

    I found this link that has a bit more information it focuses on welding though rather than asbestos.

    And this one that gives some more specifications.

    As I said – I have no experience with this type of RPE. To me it appears that the “TH” code (1, 2 or 3) is for the RPE classification: I found this info on another supplier catalogue

    TH1 – Low filter performance (90% minimum efficiency)

    TH2 – Medium filter performance (98% minimum efficiency)

    TH3 – High filter performance (99.8% minimum efficiency)

    And the “P” with a number after it will determine the filter classification –

    Particulate filter respirators are classed as:

    Class P1 – Intended for use against mechanically generated particulates of sizes most commonly encountered in the industry. Minimum efficiency 80%.

    Class P2 – Intended for use against both mechanically and thermally generated particulates. Minimum efficiency 94%.

    Class P3 – Intended for use against all particulates including highly toxic materials. Minimum efficiency 99.95%.

    Powered respirators with a particulate filter are classed by efficiency:

    Class PAPR-P1 – 95% minimum efficiency

    Class PAPR-P2 – 99% minimum efficiency

    Class PAPR-P3 – 99.95% minimum efficiency


    So from the original quote specification would it be these values?

    “Purelite Xstream full face respirator 1 x TH2 (P3) Particle Filters”

    TH2 – Medium filter performance (98% minimum efficiency) for the RPE unit i.e. hood

    Class PAPR-P3 – 99.95% minimum efficiency for the filters


    Sorry I cannot be of more help. It seems the critical piece is what the rating of the filter in use is. The final part of your post has the “THp2” category which I think would not be suitable compared to the TH2P3 which was in the first part.

    I hope someone else will come along soon with more advice.

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