Most tanners today are used to dealing with emission criteria from the automotive industry, where the initial concern was to improve technical safety by tackling the problem known as ‘fogging’. This is the term used to describe the effect produced when substances emitted from automotive components condense on the cold windows, thereby obscuring the driver’s view.

Older measuring methods simulate this situation accurately. However, in the interest of being able to work with smaller samples, thus permitting automation, new analytical technologies were developed using methods such as headspace gas chromatography/mass spectrometry to determine not just the quantity but also the quality of the emissions.

Even if the measurement parameters bear very little resemblance to the conditions in an actual vehicle, these methods still provide a useful indication of the cumulative emission potential of a leather. The following is a brief overview of the methods stipulated by various car manufacturers:

Static headspace: RAL-GZ 479 / VDA 277 (PV 3341)

Dynamic headspace: PB VWL 709

Bottle method: RAL-GZ 479 / DIN EN 717-3 / VDA 275 (PV 3925)

Fogging (gravimetric, reflectometric): DIN 75201 / ISO 6452

On the whole, the supply industry today provides products and processes that enable leather manufacturers to keep within the most common thresholds for emissions. However, these often involve higher costs and certain concessions with regard to other technical aspects.

Whereas technical safety is the prime concern in the automotive industry, it is the health aspect and air pollution control in living areas that take priority in the furniture sector. For this reason, the test conditions for furniture upholstery leathers are designed to be as realistic as possible and include other substance-related criteria such as the absence of certain preservatives or toxic substances. The differences between the requirements of the automotive and furniture industries can be summed up as follows:

Emissions from automotive leather:

* technical safety

=> extreme test conditions

=> emissions (generally) only measured in total

Emissions from furniture upholstery leather:

RAL-UZ 117 Low-emission upholstered furniture, ‘Blue Angel’ label issued by the UBA (German Federal Environmental Protection Agency)

RAL-GZ 430/3 ‘Golden M’ issued by the DGM (German Furniture Quality Association)

* health aspect of prolonged exposure

=> practice-orientated test conditions

=> substances measured individually

This presentation will concentrate on the UBA’s ‘Blue Angel’ environmental label RAL-UZ 117: low-emission upholstered furniture. The ‘Golden M’ quality label RAL-GZ 430/3 issued by the DGM is based on the same principles. Where there are major differences between the two, they will be briefly explained.

Test methods and thresholds

The aim of the UBA environmental label is to protect the environment and end-users against harmful emissions from everyday commodities, and so care is taken to ensure that the test methods used are as practice-orientated as possible. DIN V ENV 13419-1, for example, is concerned with air pollution control in living areas and is already included in RAL-UZ 38: Low-emission Wood Products and Wood-Base Products.

The test method is based on a large-volume test chamber in which the samples to be analysed are conditioned for up to four weeks under representative ambient conditions of, for example, 25°C, 50% relative humidity and one air change per hour. The air in the chamber is eventually analysed to result in a ‘snapshot’ of the emission situation.

Figure 1 shows the advantages and disadvantages of this method.

In addition to providing realistic test conditions, this process takes into account the fact that the emission levels of the majority of substances tend to subside after a short time. The higher pollution level caused by new items of furniture can be reduced by increased airing, whereas the emission level measured after four weeks can be taken to be the long-term pollution level.

This is an important aspect, as can be seen from the next diagram (Figure 2), which shows how the emission levels of various substances from a furniture upholstery leather subside.

On the basis of comprehensive studies, the German Environmental Protection Agency (UBA) has stipulated 1000 &#181g/m3 as the level at which long-term exposure to a representative mixture of volatile substances in the room air can be regarded as harmful. The medium-term aim is to reduce the limit to 300 &#181g/m3, which is considered to be no longer perceptible.

Taking as a basis this target of 1,000 &#181g/m3, a limit of <450 &#181g/m3 [at 1.5 m3/h m2] for total volatile organic compounds TVOC (C6 – C16) and <80 &#181g/m3 for total semi-volatile organic compounds TSVOC (C16 – C22) can be extrapolated for RAL-UZ 117.

This extrapolation is based on a typical furnishing set-up and the chamber conditions stipulated in the DIN and also takes into account the fact that the pollution should not be attributed entirely to the furniture.

A series of tests carried out in 2001 on 20 leather samples provides an indication of the need for an environmental label to protect consumers.

Even if this series of measurements cannot be taken as representative, it nevertheless shows that, although it is perfectly possible to produce furniture upholstery leathers with extremely low emission levels, there are still products on the market that exceed the proposed limits by a wide margin.

Analysis of the gas room using GC makes it possible to determine not just the total pollution level. Over 100 individual substances with different degrees of volatility and varying toxicological potential are routinely measured. Obviously, they cannot all be listed here, but unfortunately it has to be said, that it cannot be taken for granted that problematic substances such as benzene and dimethylformamide (DMF) will not be present.

Since particularly carcinogenic substances call for more comprehensive safety precautions, further limits were defined for these. Carcinogenic substances classified as K1 or K2 must not exceed a total threshold of 10 &#181g/m3 after three days even in the higher initial emission phase, and none of these substances must be detectable after 28 days’ conditioning (detection threshold 1 &#181g/m3).

RAL-GZ 430/3 goes even further, defining similar thresholds for mutagens and eratogens as well.

Aldehydes also come into a category of their own. The threshold for formaldehyde is 60 &#181g/m3 after 28 days, and there is a total threshold of likewise 60 &#181g/m3 for all other volatile aldehydes that can be detected by means of DNPH (dinitrophenylhydrazine), also glutaraldehyde, for example.

To obtain a more detailed picture of the emission levels, it is possible to look individually at the products used, the categories of substances emitted or the individual stages in the leather manufacturing process. There is, of course, a certain amount of overlapping. In this case, the last alternative was selected, as the various intermediates can be easily tested for their emission values.

Emissions from crust leather

As a rule, beamhouse work and tannage, whether with chrome or glutaraldehyde, have very little impact on the total emission level. Most volatile substances are generally introduced into the crust via the retannage and can be subdivided, for example, into groups of chemical compounds:

* alkanes, alkenes etc

* aldehydes (formaldehyde, glutaraldehyde, hexanal etc)

* aromatic substances, alkylaromatics etc (naphthalene, phenol)

* furans (ethylfuran etc)

* preservatives (CMK, OPP etc)

* stabilisers (phenol derivatives, BHT etc)

* plasticisers (dicarboxylic acid ester)

Figure 4, which represents the values for a furniture upholstery leather measured by means of VDA 278, shows the typical distribution of substances in a cumulative analysis of emissions.

Three conclusions can be drawn from this which also tally with the results of test chamber measurements according to DIN V ENV 13419-1:

* The absolute majority of emissions stem from the fatliquoring agents used, and not just from typical fatliquor constituents such as paraffins and waxes, but also from radical stabilisers such as BHT used to improve the fastness properties of the fatliquoring agents.

* The amount of semi-volatile organic compounds (SVOC) is often roughly the same as that of VOC. This leads to major problems in the test chamber, as the semi-volatile compounds subside more slowly.

* Substances with a problematic toxicological profile account for only a minor proportion of the emissions provided the process is carried out properly and the right products are used.

In addition to those substances whose origin can be attributed directly and unequivocally to certain processing chemicals, one frequently comes across emissions for which there is no immediately obvious explanation. These include, for example, long-chain aldehydes and alkylfurans, which are recognised by their unpleasant odour.

The most plausible explanation for the formation of these substances is the oxidative decomposition of unsaturated fatty acids contained in fatliquoring agents or natural fats. An analogous reaction mechanism and its intermediates are also considered responsible for the formation of chromate in leather on exposure to UV light.

In modern processes, however, the emission levels of these aldehydes are well below the stipulated thresholds. The same applies to glutaraldehyde from wet-white tannage and to traces of formaldehyde which are introduced by auxiliaries and retanning materials and which are bound sufficiently firmly to the leather matrix.

Summing up, it can be said that most of the emissions from crust leather could be reduced by optimising the process:

* alkanes by using low-fogging (refined) fatliquoring agents (‘automotive’ products)

* furans and aldehydes by thorough degreasing and the use of oxidation-resistant fatliquoring agents

* formaldehyde by optimising the processes or using formaldehyde-free products (see ‘Free formaldehyde – a practical guide’)

As regards other groups of substances, eg stabilisers and plasticisers, it is much more difficult to optimise the process, for one thing because manufacturers of processing chemicals look upon these substances as a means to an end in the product formulation. Their effect on the leather’s properties is considered more important than the emission levels.

Emissions from the finishing process

Most modern finishing systems are based on aqueous polymer dispersions. This does not mean, however, that no organic substances can be emitted. The reactive components on the market are generally still diluted with anhydrous solvents, and some product groups – eg dyestuffs – often require a co-solvent to ensure uniform distribution.

Last but not least, organic solvents are added to finishing formulations to improve the processing properties, give better flow-out or obtain special effects. And even the aqueous polymer dispersions themselves are not always solvent-free, eg if the NMP process was used to synthesise the polyurethanes.

As in the case of crust leather, the emissions from the finishing process can be subdivided into:

* solvents ‘for application’, flow control agents etc (MOP, MOPA, EEP, toluene, xylene, glycols, ketones, alcohols, esters etc)

* solvents for the production of polymers (NMP, NEP, DMF, acetone etc)

* plasticisers (dicarboxylic acid ester)

* stabilisers (phenol derivatives, BHT etc)

As many of these substances are readily volatile, there are basically two ways to optimise the process:

=> The amount of solvent used can be minimised and products can, if necessary, be replaced by non-volatile functional chemicals, eg polysiloxanes as flow control agents.

=> By modifying the drying conditions and by ventilating, residual solvent can be removed before the leather is processed into furniture upholstery, thereby reducing the emissions from the finished product.

The measures commonly taken to solve emission problems can be seen in Table 1.


Preservatives are of particular interest when it comes to awarding the ‘Blue Angel’ label, not just because of the associated emissions, but also on account of their properties in general. Under the terms of the environmental label, leather must contain no toxic or highly toxic constituents. This includes not only polychlorinated phenols such as PCP, which have now largely disappeared from the market, but also, for example, TCMTB, which is widely used. Carcinogenic constituents must not be present either.

As regards preservatives for wet-blue and wet-white, that only leaves the phenolic active ingredients chloro-meta-cresol (CMK) and ortho-phenylphenol (OPP) and N-octyl-isothiazolinone (N-OIT), for each of which stringent threshold values apply (calculated in each case on the weight of the finished leather and determined by extraction):

* OPP <500 mg/kg,

* CMK <300 mg/kg,

* N-OIT <100 mg/kg

These thresholds pose various problems which will have to be investigated in the future.

=> The thresholds refer to the preservative content calculated on the weight of the finished leather. In the preservation of wet-blue and wet-white, however, preservative manufacturers base their calculations on the weight of said intermediates.

In the course of the retanning, drying and finishing processes, different amounts of substances are introduced into the leather, the leather is washed several times and finally dried. Consequently, the concentration of preservative decreases progressively until the finished leather is obtained. So far, however, it has not been possible to produce a reliable correlation between the process parameters and the preservative content and so each process must be considered individually.

=> Abrasion tests have shown that virtually none of the permitted active ingredients are released on contact with the leather, even in the presence of perspiration and that they, therefore, pose no threat to the end-user or the environment. This suggests that the only relevant test value is the emission of those preservatives that are routinely included in the test chamber method. Following analysis of the toxicological data, the UBA has proposed the following thresholds as an acceptable pollution level for interior air:

OPP <23 &#181g/m3

CMK <12 &#181g/m3

N-OIT <1 &#181g/m3

Initial results obtained by the test chamber method indicate that the permissible active ingredient concentration in leather could be increased considerably, at least for OPP and N-OIT, without exceeding the emission limits. The following values were measured, for example:

=> Studies conducted at the College of Tanning in Reutlingen, Germany, show that, with chrome-free leathers in particular, active ingredient concentrations significantly higher than the threshold values are needed to obtain a degree of preservation that will guarantee problem-free processing.

The DGM quality label RAL 430/3 takes account of this fact and requires only the absence of polychlorinated phenols (penta-, tetra- and trichlorophenols) as biocides.

Other requirements

Even if they are not relevant to emissions, the other requirements of the ‘Blue Angel’ label should briefly be mentioned:

* Both chrome-tanned leathers and leathers tanned without chrome are equally permissible. Chrome-tanned leathers must be tested for chromate according to DIN 53314 => threshold 3 mg/kg

* Toxic, highly toxic and carcinogenic substances, chlorinated paraffins => universally prohibited as constituents; individual substances tested in the emission chamber

* Dyestuffs and pigments => ban on azo dyestuffs with carcinogenic amines, sensitising pigments and certain heavy metals (thresholds)


RAL-UZ 117 ‘Low-emission upholstered furniture’ primarily limits emissions from upholstered furniture and its constituent parts, eg leather, in the interest of consumer protection.

The use of selected processing chemicals and optimised processes makes it possible to reduce emission levels in leather production where necessary with existing products and thus keep within the threshold values of the environmental label.

Much of what is known so far about emissions is based on VOC and FOG studies and must be verified or optimised in the emission chamber.

When preserving intermediates, it is important to use the right products in the right quantities. However, it will be extremely difficult to obtain reliable long-term protection with the threshold values currently in force.

The DGM quality label RAL-GZ 430/3 is more stringent than the ‘Blue Angel’ as regards the composition of emissions but offers greater flexibility in the preservation process.

Where the problem of preservation can be solved by using appropriate processes, the ‘Blue Angel’ environmental label would appear to be technically feasible and the amount of work involved acceptable. It can, therefore, be seen as a suitable marketing tool.

From the technical point of view, the ‘Golden M’ quality label issued by the German Furniture Quality Association is more or less equally good, and also takes into account the special circumstances presented by the preservation of intermediates.


I would like to thank Frau Raphaela Rothenkirchen, Herr Christopher Henzel and Herr Frank Silberkuhl for the many hours of practical work they put in.

I am also extremely grateful to Dr Oliver Kretschik, Dr Wolfgang Wenzel, Dr Frank Jungnickel and Dr Haiko Schulz for the valuable discussions, information and documents.


RAL-UZ 117: Emissionsarme Polstermöbel; LANXESS (Hrsg); Leverkusen; 2004.

Vergabegrundlage für Umweltzeichen, Emissionsarme Polstermöbel RAL-UZ 117; RAL Deutsches Institut für Gütesicherung und Kennzeichnung e V (Hrsg); Sankt Augustin; 2004.

RAL GZ 430: Güte und Prüfbestimmungen; Deutsche Gütegemeinschaft Möbel e V (Hrsg); Nürnberg; 2002.

Free formaldehyde – a practical guide; M Kleban, Leather International; 2003; pp26 – 29.

Vergleichende Untersuchungen an Wet White Gerbsystemen; C Hauber; 57. VGCT Fachtagung; Koblenz; 2005.