Odour/VOC Removal Filters
Frequently Asked Questions
Q1: What are Volatile Organic Compounds (VOCs)?
VOCs refer to a class of organic chemical compounds that have significant vapour pressures
(volatile) at room temperature (vapour pressures greater than 0.07 kPa). Many contain oxygen,
nitrogen, sulphur or halogen atoms.
Due to the different physical and chemical properties of the individual VOCs, they are affected in
varying degrees by VOC destruction techniques. In general, the main factors in selecting the right
treatment technology are:
• The VOC and its physical and chemical properties
• The volume/concentration of the contaminants
• Presence of other contaminants
Q2: What are tricresyl phosphates (TCPs)?
The TCPs are organophoshate compounds.
They are present as anti-wear additives in certain formulations
of aircraft turbine engine oils and some aircraft hydraulic fluids,
which typically contain 1 to 5 % TCP by weight. (ref: ASHRAE
Guideline 28 “Air Quality within Commercial Aircraft”) Although the
ortho isomer of TCP, tri-ortho-cresyl phosphate (TOCP), has often
been studied in the past, there are a total of 10 different isomers.
Q3: Do carbon filters remove odours/VOCs?
CH3
CH3
O
O
P
O
O
CH3
For aircraft cabin air, and other industrial
transport systems, gaseous removal is
typically performed using adsorption devices.
A popular adsorbent is activated charcoal,
which has a high internal surface area,
and the pollutant molecules attach to
active sites on these internal surfaces.
It is effective at removing VOCs associated
with engine oil/oil degradation.
The Pall carbon adsorbent is effective at adsorbing
volatile organic compounds. Test results have shown a removal
efficiency of 65-73 % when challenged with TCPs in the gaseous
phase at the Fraunhofer Institute in Germany in 2010. The Pall carbon
adsorbent has an initial removal efficiency of >80 % with toluene (ISO11155-2). Toluene is the
standard challenge in laboratory testing of adsorbents
Q4: Do carbon filters only remove the smell and not remove the
associated harmful chemicals?
The Pall carbon adsorbent is effective at adsorbing VOCs. Where harmful chemical compounds
exhibit detectable odours, removal of these compounds from the cabin air by adsorption on to
carbon based filters will, of course, eliminate the smell.
Q5: Do carbon filters remove ozone, carbon monoxide (CO) and carbon dioxide (CO2 )?
Carbon adsorbents have some effectiveness with ozone but not with carbon monoxide and carbon
dioxide. FAR 25.831 specifies the maximum allowable levels of CO and CO2. These have been
monitored in other air sampling programmes and have been found to be within acceptable levels.
(ref EN 4618:2009 “Aircraft internal air quality standards, criteria and determination methods”).
Q6: Do High Efficiency Particulate Air (HEPA) filters remove TCPs?
HEPA filters are designed to remove particulate, not gaseous, contamination. Although TCP vapours will
not be removed, aerosolized droplets can be adsorbed on the HEPA filter media and therefore used
cabin air filters (and other aircraft surfaces) may contain small residue of TCPs. Note: HEPA filters are
usually rated at 99.99% sodium flame test efficiency or the equivalent 99.97% D.O.P. (Di-Octyl
Phthalate) efficiency. According to ASHRAE Standard 161-2007 “HEPA filters….. shall meet or exceed
the requirements of Institute of Environmental Science and Technology IEST-RP-CC007.2 Filter Type "A,"
or MERV 17 or H13 according to EN 1822-1, and shall provide a minimum of 99.97% collection
efficiency for 0.3 micron particles”.
Q7: Where are the filters fitted in the environmental control system (ECS)?
In a typical commercial aircraft, the air supplied into the main cabin consists of approximately 50%
outside air from either the engine’s compressor stage (engine ‘bleed air’) or the Auxiliary Power Unit
(APU), which is mixed with approximately 50% of filtered, recirculated air. (Note however, that some
aircraft designs are now moving to ‘bleed air free’ ECS). The cabin air filters are located in the
recirculation loop and these can be either HEPA filters or combined HEPA/Carbon filters. However, some
particulate contamination, odour causing compounds and VOCs and semi-volatile organic compounds
(SVOCs) may enter from the outside air system where filtration is not normally provided. The air supplied
to the cockpit can come from a number of sources (e.g outside air from the engine or APU or a
combination of outside air and recirculated air from the mixing chamber) and the supply is dependant
on the aircraft ECS configuration.
Q8: What is the recommended filter element change-out interval?
There is no definitive time interval for replacing a HEPA filter or an odour removal filter element.
The time interval varies between aircraft types and between aircraft systems. Pall will work with the
airlines and the aircraft manufacturers to determine the optimum service interval for the specific
operating environment.
Q9: Which aircraft are fitted with odour/VOC filters?
At present, Pall has designed combined HEPA/Carbon filters as an option on the Airbus A320 family and
Airbus A330/A340 family where they are fully inter-changeable with the existing particulate HEPA cabin
air filter elements. Pall is also carrying out an in-service evaluation of a combined Particulate/Carbon filter
on a commercial aircraft where it is designed to filter the cockpit supply air.
Q10: Is there a danger to the maintenance personnel by removing used odour removal filters?
There is no more risk involved in replacing a used HEPA or carbon filter than carrying out general
maintenance on any aircraft part that has been in service for a number of years. Maintenance staff who
may be concerned about the general accumulation of dust and debris on cabin air filters should wear
the same personal protective equipment as for other similar aircraft maintenance tasks.
Pall Aeropower
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in your area, please go to www.pall.com/contact
Portsmouth - UK
+44 (0)23 9230 2399 telephone
+44 (0)23 9230 2203 fax
areospace@pall.com
Because of technological developments related to the products, systems, and/or
services described herein, the data and procedures are subject to change without
notice. Please consult your Pall representative or visit www.pall.com to verify that
this information remains valid.
© Copyright 2011, Pall Corporation. Pall and
are trademarks of Pall Corporation.
® Indicates a trademark registered in the USA. Filtration. Separation. Solution.SM is a service mark
of Pall Corporation.
AEOVOCEN
Printed in the UK.
January 2011