The T.35 filter was the standard small filter for most territorial groups and, later on, of the Italian army. The production ceased in 1943, but it saw use until the '80s as a training filter.
The Dirzepo, Dirzepest, Pir. 35, P.C. 35 and R.S. 37 filters were a variant of this filter, identical in most aspects with the exception of colour and markings and some time the shape of the top.
Overview[]
Insides of the T.35 filter
The T.35 was painted dark brown and contained the following layers, from top to bottom:
- A thin layer of particulate filtering material (either wadding or cellulose), used mostly to avoid loose granules from being inhaled
- A layer of "Z" type granules, made of either pumice or soda-lime soaked with sodium carbonate and zinc oxide
- A layer of activated charcoal, obtained mostly from the hard parts of various fruits
- A layer of filtering, to protect against fumes and arsines, composed of a disc of pressed wool soaked in a solution of alcohol and benzol with the following compounds: bakelite (28,3%), colophony (66%), ethyl phthalate (4,7%), calcium oxide (1%)
(Note: it's been confirmed that no asbestos was ever present in the filter[1][2]).
These layers were pressed by metal diaphragms, with the bottom creating a small gap between the inlet and the filtering mass so that the air could spread and ease breathing resistance. Before being opened, the bottom intake is covered by a small sheet of waxed canvas and the top is closed using a 40 mm cap, with all of this bound with a string closed using a small lead seal. After the filter has been opened for the first time, it could be closed again using the 40mm cap and a small rubber seal attached through a string to the filter. The height and weight of the filter vary with the date of production and manufacturer.
The filter could protect the user from any war gas known at the time for up to 7 hours, with the exception of arsines which were not filtered as efficiently and CO, which wasn't filtered at all (requiring instead a dedicated filter).
Markings[]
The T.35 filter has three main markings:
- The two symbols on the top near the filter thread are the manufacturer's logos.
- The inscription on the side is the name of the filter. Note that the font changes between some companies.
- The inscription at the bottom is the date of production.
Spanish recovery[]
After the end of the Spanish Civil War, the government set out to gather all of the various gas equipment issued by both sides, in an effort to re-issue said equipment in a standardized way. The filters that were found had a label added around them that said: "Filtro procedente de recuperación" (recovery filter), and under that the number of the factory (for example: "Fábrica n.3").
UNPA[]
T.35 kits made specifically for the UNPA (Unione Nazionale Protezione Antiaerea, national union for air-raids defence) used a specially marked T.35 filter. The filters made by Pirelli for this purpose were coloured orange, while I.A.C. ones were the usual brown and had "U.N.P.A." marked on the side.
