Kick-off Levels (2014)

Kick-off levels are occupational exposure values for substances without a formal exposure limit, but with (limited) health information (H3##-statements). The original kick-off levels from 2005 have been updated using H-phrases, 2013 OEL databases and improved Control Banding systems. Below you will find the results. We presented the draft results of the kick-off levels 2014 at OH2014, the BOHS conference in 2014. Our presentations at this conference are here.

 

Summary

Below are the the kick-off levels 2014. They are based on the Control Banding Scheme of COSHH Essentials for exposure to dusts/aerosols and IFA’s GHS Spaltenmodell for the exposure to gases/vapours.

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What are kick-off levels?

In 2005 we published a method for the determination of 8-hour exposure limits for substances without formal limits, but with risk phrases (R-phrases) concerning health or toxicological effects. These were called kick-off levels, because they were a conservative starting point for any further development of a health-based in company exposure limit , based on an analysis of all health-based scientific information (animal studies and epidemiology) available at that time.

 

In the 90s of the last century “Control Banding” schemes with grouped R-phrases of substances into so-called hazard categories were developed. The kick-off levels 2005 we published were based on the distribution of OELs of substances in R-phrase-hazard categories. It turned out that kick-off levels based on the German TRGS 440 hazard categories were much more robust than the others (COSHH, ECETOC, ILO, [DUTCH] SOMS), due to the differences between the distribution of OELs of this scheme. The proposed OELs in het COSHH Essentials scheme turned out to be too optimistic.

 

Kick-off levels are defined as the 10-percentile of the OEL distribution of the substances in a hazard category. This means that 90% of the OELs for substances in that hazard category have a higher value than the kick-off level. This also means that the absolute value of a kick-off level is on the conservative side.

 

If limiting the exposure to below the kick-off level is technically feasible, the need to conduct (expensive) additional studies for a more unbiased and probably higher health-based limit value is less necessary.

 

The kick-off level method has been received positively enthousiasm. It has have been given a sound place in the realm of the Dutch exposure assessment policy. The Dutch Labour Inspectorate accepts kick-off levels for compliance testing (if there are no other OELs available).

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Why upgrading the kick-off levels?

Since 2005 much has changed. First, the R-phrases are replaced by H/EUH-codes (as part of the REACH/CLP system). Furthermore, the DOHSBase Compare database with OELs has more than doubled in size. Additionally the international tendency to set OELs at lower levels may have shifted the OEL distribution downwards. Finally, the “Control Banding” schemes we used in 2005 have also been modified (H-statements instead of R-phrases) and improved by the respective authorities.

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Translation from DSD to CLP

Since the CLP Regulation has entered into force, the use of R-phrases will decrease. For single substances its use is not allowed anymore. This means that the dataset used to calculate the kick-off levels should be converted from R-phrases to H-phrases.

One of the challenges is the fact that the ‘translation’ of R-phrases for the new H-statements is not a simple 1-on-1 replacement. The reason for this is that the borders of the groups of the toxicological groups/categories are not the same for the old (DSD) and the new (CLP). For example, see the diagram below.

Lethal; route LD50 (mg/kg)

R-phrase DSD

CLP hazard class

H- Phrase CLP

Oral 5

28

Acute tox. 1

300

oral 5-25

28

Acute tox. 2

300

oral 25-50

25

Acute tox. 2

300

oral 50-200

25

Acute tox. 3

301

oral 200-300

22

Acute tox. 3

301

oral 300-2000

22

Acute tox. 4

302

 

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Control Banding Systems

As in 2005, substances with an OEL are assigned to a hazard class in a Control Banding System. Compared to 2005, some of the known Control Banding schemes have been adjusted to CLP. Kickoff level assessments are performed using the following H-statement based Control Banding schemes. Click on the name of the system for more information on the control banding systems:

▪    COSHH Essentials (United Kingdom)

▪    DGUV-IFA Spaltenmodell (Germany)

▪    EMKG (Germany)

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Database DOHSBase Compare

The data set used is DOHSBase Compare (version 2013/14) with nearly 3000 chemical substances with one or more national, international and/or company OELs (as TWA 8 hour): these values are used for the occupational hygiene advice and compliance verification. DNELs and DMELs were excluded but will be used in the future to test their relation with their notified CLP classification. Furthermore the following OELs were removed:

  • Exposure limits with a different dimension (respirable dust, fibres, fibril, CFU, vol.%, EU/m3, glycine unit/m3), with the exemption of µg (micro), pg (pico) and ng (nano). The latter were converted to mg (milli).
  • Substances that have been evaluated (for example, by the Health Council of The Netherlands and SCOEL), but for which no limit could be established.
  • In case of multiple TWA 8 hr OELs for a substance, the OELs from lower hierarchy for OELs were removed.

The remaining, (merely health based) OELs are linked through their CAS-number with a database containing the harmonized CLP classification (symbols and H-statements) of nearly 8000 substances. The linking of OELs and H-statements leads to a database with more than 900 substances with H-statements and a TWA 8hour OEL. These are the data with which the analytical computations were performed.

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Analysis

Using the substances, their TWA 8hour OELs and hazard classifications, the shape and location of the OEL distribution was determined per hazard group of the different Control Banding schemes (A, B, C, D, E). Based on the ”best fit” with the lognormal distribution, the 10%-tile of the TWA 8hour OEL distribution was estimated using the Wilks’ unbiased Student-t lower tolerance limit or nonparametric for each hazard class.

 

De Generic Exposure Values of the Control Banding schemes and the lower limits of the Control Bands were compared with the associated OEL distribution.

The following methods were used:

  • Lognormal probability plot and boxplots (HYGINIST)
  • Shapiro and Wilk test for distributional goodness-of-fit with Regression for censored samples (HYGINIST)
  • ANOVA to test the differences between the hazard groups (BW_Stat)

Occupational Exposure Limits are, by definition, greater than zero, often have values between 0,01 and 100 mg/m3 and are rarely greater than 1000 ppm or mg/m3. OEL distributions are therefore skewed. The software program HYGINIST was used to investigate whether the statistics of the lognormal distribution could be used to estimate the lower limit of the distribution. The Geometric Mean (GM) is the measure of the location of the OEL distribution. The geometric standard deviation (GSD) is the measure of the dispersion. The percentiles are calculated using OEL% = GM * GSD^k, where k is the Wilk factor for the unbiased estimate of the percentile.

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Results

The distributions of the OELs in ppm and mg/m3 (y-axis) per hazard class (x-axis) for three schemes (COSHH, TRGS600 and EMKG) are shown in the tables below, together with the statistical data of each distribution. The log-normal shape fits best between the 10%-90%-tile. Where necessary censoring is used to anticipate deviations in the tail. The 10%-90%-tile is a measure for the bandwidth (range).

The bandwidth for all three schemes is fairly large for each hazard class: 2 orders of magnitude for the aerosols and to 3 orders of magnitude for the gas / vapor OELs.

All Control Banding schemes show a significant downward trend of OEL distribution and hazard group. This decrease attenuates as the hazard group becomes more toxic (from A to E). From the various statistical functions (linear, logarithmic, polynomial, exponential, power series), the negative exponential function describes the relationship between values and hazard class the best.

 

In the box plots (page 2), the vertical rectangle represents 80% of the limit distribution valve and the vertical line the whole bandwidth (range) again. For all three schemes the current aerosol OEL’s are limited upward to 10 mg/m3.

In each box plot the comparison of the Generic Control Value is presented for each Hazard Class. The lower yellow line in the box plots represents the Kick-off OEL level. In the table above the box plots the kick-off OELs are presented in figures.

 

Results of the OEL calculations :

 

Conclusions

The grouping of the H3## statements of COSHH essentials offers according to our findings the best fit for the establishment of kick-off levels for aerosols. For gases and vapors the grouping of DGUV-IFA GHS Spaltenmodell provides the best fit. See for the values of the kiick-off levels per Hazard Group (and corresponding H-statements) the table at the top of this page.

 

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