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Working with hazardous substances (GHS)

Based upon the labelling according the Globally Harmonized System (GHS).

For more information about the rules about labelling see: Labelling hazardous substances (WMS or GHS).


Under the Working Conditions Act an employer is obliged to have a policy in place that limits the risks for safety and health for the staff members as much as possible. This also applies to the situation in which hazardous substances are used.

Hazardous (or toxic) substances are understood to be:

  • Single chemical compounds and elements (e.g. toluene, lead, hydrochloric acid);
  • Mixtures of varied composition (e.g. petrol, paint);
  • Mixture released as contamination, the composition of which is not always known (e.g. welding smoke, reaction mixtures, exhaust fumes).


The Working Conditions Decree contains a number of obligations in the area of the registration, packaging, designation and safe storage of hazardous substances. Also other legislation is relevant in this context, such as the Environmental Management Act (WM), the Pollution of Surface Waters Act (WVO), the Pesticides Act.

The legislation relating to carcinogenic and reprotoxic substances is described in the UT guideline “working with carcinogenic and reprotoxic substances”.


Statutory provisions are in place for hazardous substances in the workplace. Most of these can be found in chapter 4 of the Working Conditions Decree. An important article is article 2 of this chapter. Briefly, this article boils down to the following:

  • If staff run a risk of exposure to substances that may be disadvantageous to their safety and health, the employer is to identify the risks, taking into account the nature, extent and duration of the exposure;
  • This identification of risks is to include at any rate the substances involved, the situations which may involve exposure, and how this can take place.

In addition, the exposure level during the activities is also to be identified.


In order to assess the nature of the exposure, the employer is held to keep a register containing the hazardous substances present. Within the UT the GROS system is used for this purpose. Hazardous substances in this context are the substances which under the WMS are to be classified into one of the hazard categories of this Act (see for this the UT guideline Storage of hazardous substances. The obligation applies to the WMS hazardous substances ‘which with some regularity’ and ‘due to the nature of the activities’ are present within the organisation.


At the UT the hazardous substances are in particular present in the buildings of the ‘technical’ faculties.


An identification of risks is, according to the statutory standards, to focus on the nature, extent and duration of the exposure of the staff member(s) to the hazardous substances. For the UT this means that it is important in particular to identify ‘how’ and ‘with which substance(s)’ exposure can occur. The following is to be taken note of in this context:

I Identity of the substance or mixture worked with (in the early, intermediate and end phase)

  • Identity of the substance
    Register the chemical name and CAS number and any limit values of the substance (MAC). If the CAS number of the substance is unknown, (e.g. in case of newly synthesised substances) the chemical name/structure formula will suffice
  • Identity of the mixture
    Register per component the percentage and CAS number

II Data on the risks of the substance or mixture. Sources of information are:

  • GROS system (System at the UT for the registration of hazardous substances);
  • The supplier’s security information sheet. A supplier is obliged to provide a safety information sheet. This sheet is to be present at the workplace.
  • Chemfix (ChemWatch, system with a lot of MSDS).
  • Chemical cards book or other literature on chemicals;

(If no or little information is available on the substance, similar substances can be referred to, the details of which are known), or the AMC of the faculty can be consulted.

III The nature of the activities performed. The following possibilities can be applicable:

  1. The process takes place in a closed system: Under normal circumstances, there will not be any exposure. Exceptions are calamities, build-up or break-down and maintenance of the system. The risk of exposure is normally low.
  2. The process runs via a semi-closed system (e.g. a bath with lid, a fume cupboard) and substances are involved which do not evaporate, do not create dust particles and cannot be absorbed by undamaged skin: The risk of exposure is limited.
  3. The process runs via a semi-closed system and substances are involved which evaporate at 20 °C, create dust particles or can be absorbed by undamaged skin: The risk of exposure is moderate.
  4. The process runs via an open system and substances are involved which do not evaporate, do not create dust particles and cannot be absorbed via undamaged skin: The risk of exposure is low.
  5. The process runs via an open system and substances are involved which evaporate at 20 °C, create dust particles or which can be absorbed by undamaged skin: The risk of exposure is high.

IV The way in which exposure can take place. This involves exposure which would occur if no protective measures are taken (so-called potential exposure).

  • describing the nature of the substance(s) used and the related hazards in solid, liquid or gas condition:
    • as to solid substances: easy dissemination of powders or crystals;
    • as to liquids: if there is a risk of splashing, a vapour (aerosol) is easily formed;
    • as to gasses: weight of the gas (in relation to air), creating of mists.
  • checking whether there will be exposure if aerosol or mist is breathed in via skin or mouth;
  • taking into account any reinforcing effects that may occur during exposure to several substances (e.g. in combination with solvent, easy absorption via skin); taking into account any hazardous environmental factors in the research activities (working at high or low temperature, using high pressures and such).
  • it is to be investigated which calamities may occur during the various steps of the process; taking into account the researcher’s own installation, any installations in the same compartment and other environmental factors.

V Information on the use of the substance or mixture (litres or microlitres), the storage location, knowledge of the staff involved.

VI Based on the identification of the above point, (groups of) staff can be designated who run a risk of being exposed (for example: scientific researchers, students and technicians). 
If the level of exposure is difficult to establish, but there is a risk of harmful concentrations of a substance, taking environmental measurements may be necessary. For this contact an expert of the Human Resources department (HR).

VII Plan of action

State the measures to be taken to avoid exposure.

  • If source control is not reasonably feasible: ventilation, separation of humans and source or in extreme cases using personal protection gear for protection against rest risks. Indicate which organisational or technical measures need to be taken.
  • What needs to be done to avoid calamities (acknowledged in step IV).



Packaging containing hazardous substances is to be recognisable as such. The label on the packaging is to contain the following information:

  • Chemical name of the hazardous substances;
  • Any hazard symbols and designations;
  • H/P sentences.

This means that also bottles, erlenmeyer flasks and such are to be provided with such labels if the contents after production or dousing is kept (for longer than one day). For solutions used during one day only, the chemical name of the hazardous elements suffices.

The storage of these substances is to be in accordance with the UT’s environmental permit (in accordance with PGS 15 guidelines or equivalent). See UT guideline Storage of hazardous substances.

Spilled (waste) substances are to be cleared immediately. Any spilled remnants of either organic solvents, acids or bases can be absorbed by a universal absorption agent (e.g. Chemizorb). All laboratories are to store an absorption agent.

Within the UT detailed rules are in place relating to waste collection and the removal of hazardous substances (see Waste management regulation University of Twente). Compliance with these rules is compulsory.


In consultation with the building’s in-house emergency and first-aid service, it is to be examined whether a special calamities procedure is to be put in place. If so, this is to be included in the information provided to staff and in-house emergency and first-aid service workers involved. In several laboratories substances are worked with which in the event of unintended exposure or unintended reactions, may lead to acute poisoning symptoms. These symptoms may, if not responded to adequately and quickly, result in death. Examples of these substances are among other things cyanide compounds and hydrogen fluoride. The UT has a first-aid protocol in place for such substances.


The use of a PAGO ‘hazardous substances’ for laboratory staff is controversial. If exposure to hazardous substances may be involved and this also leads to observable health risks, it is obligatory to have the staff member involved undergo a medical examination (AGO). Precisely how the examination is to take place, depends entirely on the substance(s) used during work. There should be consultation with the working conditions service (where the actual examination is also to be performed). In practice, it turns out that it is often difficult for employees working in a laboratory to perform a specific AGO, because staff members are exposed to different substances. Besides, there are not many substances for which validated examination methods exist. If an examination is useful, the level of the substance in the blood, urine or breath may be examined. Points of attention for performing a AGO are:

  • The working conditions service is to be aware of the conditions and circumstances of the exposure;
  • A medical file is to be prepared in which the staff member involved’s occupational history is also to be included;
  • The working conditions service is to have a personal talk with the staff member.


Staff members, students and third parties are to be informed of the risks they run by working with certain substances. In this context the following is to be pointed out to the staff member:

  • The possible dangers to health as a result of exposure to the substances and vapours used for the activities;
  • The safety and preventive measures taken and the reasons for doing so;
  • The means of protection made available and the way in which these are to be used and maintained;
  • If applicable: the existing rules, content and purpose of a periodically to be repeated medical examination.


When working with hazardous substances wearing safety goggles and a laboratory coat is compulsory. Depending on the nature of the activities (see under Performing an RI&E) in addition to these also other personal protection gear is to be worn. For this also refer to the guideline of working with personal protection gear.

Literature/further reading

  1. Working conditions information sheet number 18: Laboratories (publisher SDU)
  2. Working Conditions Decree, Chapter 4
  3. CPR-15-1, Storage of hazardous substances in packaging; storage of liquid and solid substances (1 to 10 tons). Committee for the Prevention of Disasters.
  4. Environmental permit University of Twente


The table below shows combinations of groups which:

  • May not be stored collectively ( - )
  • May possibly be stored in the same compartment ( +)

Whereby A = oxidising substances

B = flammable liquids

C = flammable solids

D = (very) toxic substances

E = corrosive/caustic substances

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