Occupational exposure to silica dust in France: an ongoing concern

Objectives Crystalline silica is found in many construction materials. Although it is one of the oldest known occupational exposures, new exposure contexts have emerged in recent years. In 2021, France classified work involving exposure to respirable crystalline silica (ie, silica dust) generated by a work process as carcinogenic. In order to assess exposure in the French workforce between 1947 and 2020, we developed a silica job-exposure matrix (JEM) for the Matgéné program. Method The JEM was linked with occupational data from different population censuses (1982, 1990, 1999, 2007 and 2017). The proportions and numbers of workers exposed to silica dust in France at these various census time points were estimated and described by sex and industry for 2017. Results After decreasing between 1982 and 1999, the proportion of workers exposed to silica dust remained stable at 4%, representing 975 000 workers in 2017. Exposed workers were mostly men (93%), and most worked in the construction industry (64%). This was also the industry where the majority of workers were exposed to a level above the French 8-hour time weighted average occupational exposure limit (TWA-OEL). Conclusion A large number of workers in France were still exposed (some highly) to silica dust in 2017 so this agent still poses an occupational health concern. The results of this study provide key information about the continued surveillance of the evolution of exposure to silica dust. In a few years, it will be possible to quantify the impact of the 2021 regulation in terms of proportions and number of workers exposed to silica dust.


Objective of this notebook
This notebook presents the free crystalline silica dust job-exposure matrix (called silica-JEM) created in the frame of the Matgéné programme.This JEM gives an assessment to respirable free crystalline silica dust for each job considered as exposed, from 1947 to 2020.
It is an update of the existing silica-JEM assessing exposure up to 2007.This update consisted in assessing the exposure for the 2008-2020 period and transcode the silica-JEM in the newest French job classifications for all the periods.

Description of the agent a) Silica
The chemical element Silicium, Si, is a major component of the earth crust (around 25%).It is mainly found as: • free silica: white or colourless hard solid, with a tetrahedron (SiO4) • silicates: SiO4 tetrahedron as basic pattern too but combined with different metallic oxides (iron, magnesium…).
Silica and silicates can be crystalline (the pattern is regularly repeated in the space) or amorphous (without fixed structure).All these forms can be natural or man-made/synthetic.

Classification and regulation
• International Agency for Research on Cancer (IARC): crystalline silica was classified as carcinogenic for human (group 1) in 1997, for lung cancer.
• European Union: in December 2017, the European Union classified "work involving exposure to respirable crystalline silica dust generated by a work process" as carcinogenic.This classification was translated in the French law by the order of 26/10/2020.Since January 1 st , 2021, these works are considered as carcinogenic in France; this classification will make it compulsory to monitor exposure and to avoid dangerous work process for example this substance must be removed or substituted or, when it is not possible, the exposure must be the lowest as possible.
Occupational exposure limit (OEL) The order n°2008-244 of the 07/03/2008 is the current regulation in place.The classification as carcinogenic did not change these values.
There are the same values for the 8h TWA-OEL, defined by the order 97-331 of the 10/04/1997 and the one of 21/03/1983.

Occupational disease tables
In France, employees are covered under the general insurance scheme.This system is administered by the occupational accidents and diseases branch of the French social security system and funded by mandatory contributions from employers for each of their establishment.
To be considered occupational in nature and lead to compensation, a disease must appear on one of the occupational disease tables (French database) and be identified as directly linked to the www.santepubliquefrance.fr professional activity by the complementary recognition system for occupational diseases.(source: www.inrs.fr) Diseases linked to the crystalline silica exposure are listed in table 3.

JEM development
Nowadays, crystalline silica is the only form to be classified as dangerous for health.Consequently, this JEM assesses the exposure to the free crystalline silica dust only.
The silica-JEM assesses the occupational exposure to respirable free silica dust (diameter >5µm).
The JEM was developed using the expertise of two industrial hygienists (IH) specialised in JEM (https://www.inrs.fr/media.html?refINRS=BD%201).The measurements helped the expertise by giving information about some tasks or some occupations (mostly on the intensity of the exposure).These data did not give information for every combinations and were not used to automatically fill the JEM cells.

Classifications used in the JEM
Assessment to occupational silica exposure were carried out for each couple occupation/industry defined with French and international classification.For industry, we used the French classification NAF

Exposure assessment indices
The JEM assesses exposure between 1947 to 2020, through three indices: • The exposure probability defined as the proportion of workers exposed in the considered job.It is expressed in percentage, following the classes defined in table 4.
Table 4: probability classes defined in the silica-JEM

Probability classes
Values in the JEM • The exposure frequency defined as the percentage of worktime during which the exposing situations occur in the workplace.It is expressed in percentage, following the classes defined in table 5.  ]95-100] 95 • The exposure intensity represents the atmospheric concentration to which the worker is exposed during exposing situations.Exposure intensity represents the mean atmospheric concentration of silica dust to which a worker is exposed during the current tasks.It also takes into account the mean atmospheric concentration in the surrounding environment.The proportion of exposure due to the tasks and the proportion from the surrounding environment could not be distinguished.Moreover, exposure peaks are included in the intensity assessment.This assessment takes into consideration the collective protective equipment but not the personal protective equipment as it is not possible to know if they are appropriate, properly fitted or even used.It is expressed in 4 classes (table 6).

Periods of exposure
The JEM assessment takes into account different parameters, which include the evolution of exposure during time.Different exposure periods have been defined by industry following some criteria (regulation, technical evolution…) (table 7).

Quarries
-Mines and quarries: • The first period is the same for both because 1960 corresponds to the year of application of the 11/30/1956 instruction which says that good prevention technics needs to be apply • For mines, 1980 corresponds to the application of the 12/15/1975 circular about the pneumoconiosis medical prevention • For quarries, the 09/02/1994 regulation, defining a referent dust situation led to a decrease in exposure.This regulation didn't have impact on mines because at this time, there were already closed or about to close www.santepubliquefrance.fr -Other industries: • 1970 is a period of global improvement in work situation in France in industries • 1985 and 1988 are related to the OEL application The classification as carcinogenic from January 1 st , 2021 have no impact on the silica-JEM as the study period ends in 2020.

Characteristics of the JEM
In occupational environment, free crystalline silica is mainly quartz and rarely cristobalite.It is very difficult to distinguish these two forms so they were gathered under the term "free crystalline silica" for the assessment.
Several uses of the silica could not be assessed in the JEM because of the classifications used that made exposure probability too low; it is the case for example in the production of glass wool in which silica is used as a basic material.
Some industries are not in the JEM because there were not enough information available to assess exposure.For example, in agriculture, the silica rate in the soil is different from an area to another in France and the task frequency and intensity depend on crops, the farm size etc…The indices used for assessment are not able to take into account these situations and so the jobs in agriculture is not assessed in the JEM.
Some recent studies showed new exposures for the kitchen fitter working on artificial stone.This use cannot be selected because of the job classifications used.

Extract of the JEM
Table 8 is an extract of the silica-JEM, in the PCS2003*NAF2008 version.
These lines give the exposure assessment for the unskilled industrial workers (674d) working in the manufacture of concrete products between 1947 and 2020.This job has four different periods with homogenous exposure for each one.During the whole period, these workers had the same probability of exposure: 90 % (between 85 and 95%).The mean intensity of exposure decreased from class 3 (between [0,5 ; 1 mg/m 3 [) to class 1 ([0,02 ; 0,1 mg/m 3 [) in the latest period.The mean frequency of exposure also decreased from 90% (between 85 and 95%) of the working time during 1947-1970 to 50% (between 45 and 55%) during 1999-2020.
Table 8: extract of the silica-JEM.

Publications
The JEM is freely consultable on the website: www.exppro.fr.
development and based on bibliographic and metrological researches on the work situation, regulation, exposure data, etc.Both IH validated the assessments.a) The bibliographic research A scientific, medical and technical bibliographic research was undertaken and gave information to identify and assess the work situations: regulation, evolution of the exposure level, work technics, etc. b) The exposure database An exposure database was also created; it contains 634 measurement results with 22 variables, covering all the study period.Moreover, the data from the Colchic and Scola database were added to these data.Colchic and Sola are two databases handled the INRS, the reference body for the occupational risk prevention in France, containing occupational exposure measurements.

Table 1 :
Examples of different silica forms

Table 3 :
Occupational disease tables linked with crystalline silica exposure

Table 5 :
Frequency classes of the silica-JEM

Table 6 :
Intensity classes in the silica-JEM

Table 7 :
exposure level classes