Results of literature evaluation

In the previous sections available information about the estimation of protection factors for different pieces of PPE using dosimetry, biomonitoring, in vitro studies or mathematical models have been compiled.

Concerning dosimetry studies, a large number of studies was identified that can theoretically be used to derive an exposure reduction efficiency value. The highest numbers of datasets were identified for gloves and whole body garments. However, the range of efficiency values for each category of personal protective equipment is large and it is hardly possible to identify a reason, why certain studies lead to higher or lower efficiency results. The transparency of the various publications is often low, resulting in data gaps concerning PPE properties and the assessed scenario. It is often not known if the PPE in question can be considered appropriate for the situation and the assessed substance (see also Figure 10.1).

Only few publications evaluating the methodology of PPE efficiency were found, leading to mostly inconclusive results concerning sampling method and study design.

However, as it is already known that variability in dermal exposure can be induced by different sampling methods (see e.g. NG et al. (2014)), an influence on efficiency results seems likely. So far no general recommendation concerning sampling methods can be made, as there are also substance- and situation specific aspects to consider.

Additional variability can be added by different ways of evaluating the raw data. As an example the exposure data can be reported in different units (e.g. mg/cm², mg/cm²/h) or differ concerning statistical evaluation (evaluation of single efficiency values to derive efficiency values vs. average exposures used for derivation of efficiency value;

see section 5.1).

Thus, overall the available data are able to give a general idea on efficiencies that can be expected for certain types of PPE (Table 10.1, see single chapters for further details and discussion).

Figure 10.1 Factors influencing the final efficiency value.

Table 10.1 Range of exposure reduction efficiencies for different PPE categories (without negative efficiencies and other not usable database entries (11 entries))

PPE type

In addition various, isolated pieces of information about aspects influencing efficiency have been identified, such as

 the challenge of exposure (deposit),

 personal behaviour or

 PPE characteristics (e.g. glove length, use status (old vs. new)).

However, a detailed differentiation and evaluation of the factors which are necessary to reach a specific efficiency value has not been possible. Thus, although isolated pieces of information could be identified a full understanding of the summarised efficiency values is not possible and comprehensive advice leading to a specified efficiency cannot be given.

One of the aspects that are essential for PPE efficiency is the ability to function as a barrier against a challenging substance. The material can be passed either on a molecular level by permeation or on a more macroscopic level, i.e. through pores, holes, damaged material, seams etc. by penetration (see Figure 10.4). A number of studies focus on the evaluation of these barrier properties.

Regarding in vitro studies (with animal or human skin samples) dealing with permeation or penetration of chemicals through dermal PPE, no general conclusions on protection factors can be derived. The main reasons for this finding are that

a) these studies do not reflect real-life work scenarios and

b) barrier efficiencies identified in these study types differed vastly (0-100 %) - depending on

 the respective material tested,

 the chemical investigated and

 the experimental set-up.

Thus, the predictions are always only valid for a specific chemical or mixture in combination with a specific sample material. Despite the limitations, these studies are suitable for comparative assessment of different protective materials as well as different chemicals.

Similar to in vitro studies, mathematical models that aim to predict penetration through dermal PPE do not reflect real-life conditions at workplaces. They nonetheless provide insight into factors that may have an impact on penetration through dermal PPE. For example,

- the surface tension difference (between protective clothing and chemical) and - fabric parameters such as

̵ thickness and

̵ the yarn twist factors (i.e. twists per inch or turns per inch)

were identified as important model parameters predicting clothing penetration. The experimental data generated for model development were also analysed as such and showed important parameters for experimental penetration of protective clothing, such as

 fabric type (e.g. cotton, polyethylene, polyester) and

 fabric thickness.

Regarding biomonitoring studies, the literature search for this project revealed a large amount of studies. However, only six biomonitoring studies could be used to derive dermal protection factors in the context of this project. The main reasons for this limited number of evaluated biomonitoring studies are the lack of pre-shift values, the lack of an assessment with and without dermal protection, or the study design of the biomonitoring study in general. Even the evaluated studies have major deficiencies.

Figure 10.2 Distribution of efficiency values for HEEG glove categories. The current HEEG default is marked by a black line.

Figure 10.3 Distribution of efficiency values for HEEG whole body garment categories. The current HEEG default is marked by a black line.

Due to the limitations of all the studies evaluated, the derived dermal protection factors (see section 6.3) have to be considered with caution, and a general conclusion is impossible.

Only two studies were identified reporting results from both biomonitoring and dosimetry experiments. These two studies were evaluated in the context of a comparison between protection factors derived from biomonitoring and dosimetry results. It was concluded that for these studies a comparison of the results obtained with different methods was not possible due to study limitations (see chapter 6.4.2) When the results from the literature evaluation are compared with default efficiencies of the HEEG opinion or ECETOC TRA, exposure reduction due to PPE is sometimes higher based on literature data and sometimes lower (depending on the PPE considered) (see Figure 10.2-Figure 10.3 and further figures in section 5.2). However, such a comparison involves substantial uncertainty for several reasons. For example, it cannot be excluded that the literature data may reflect (to an unknown degree) studies with inappropriate PPE for the scenario assessed. Furthermore, studies generally do not document the level of training in handling PPE, which, however, is important in the default efficiencies assumed. As a worst case it may be assumed that all studies refer to a good level of training and general occupational hygiene as long as no further information is documented. It is, however, expected that this approach will lead to underestimations of the final efficiency values and should therefore be amended by further research as soon as possible.

In particular three factors were identified which are considered to be of high relevance for the understanding of efficiency values but have so far not been evaluated:

1. Influence of the challenge of exposure

2. Influence of personal behaviour / level of training

3. Substances enhancing passage through PPE (not skin) / carrier substances.

These factors will be further discussed in the following section.