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Working with hazardous substances and gasses

Working with hazardous substances and gasses entails health and safety risks. Considerable caution is needed. Be aware of the dangers and make sure you know the local ordering procedures, working instructions and supervisory measures. These form the basis for your health and safety and that of you and your colleagues.

Which substances are considered to be hazardous?

Hazardous substances are substances or mixtures that could endanger the health and safety of employees. A distinction is drawn between:

  • acutely dangerous such as flammable and explosive substances but also intoxicating and suffocating substances;
  • dangerous over a prolonged period such as irritating substances, substances that can cause allergies, substances that can damage the airways or the nervous system, cancerous substances, reprotoxic substances and mutagenic substances.

You can recognise the hazardous nature of a substance from the hazard symbols on the package labelling and the list of Hazard and precaution statements.

What do I need to look out for with hazardous substances?

Before you work with hazardous substances, make sure you know the risks involved so that you can take appropriate risk management measures. Ask an expert, supervisor or health & safety coordinator for advice and information.

  • Do not work alone. Make sure you have a colleague (at a safe distance) who knows how to assist in the event of an accident.
  • Be aware of the risks involved with the substances. Consult the relevant Material Safety Data Sheet (MSDS) in advance. If you are not familiar with the substance or mixture then assume it is dangerous and be extra careful! In the case of volatile and risky substances always work in a fume cupboard.
  • You should preferably work standing in front of a fume cupboard with the window as low as possible; make sure that your face is always behind the sliding window.
  • Always wear a lab coat and if necessary appropriate disposable gloves (type of glove is depending on the substance).
  • Avoid contact with latex gloves if you have developed a sensitivity to latex. 
  • Wear safety goggles if using strong acids or carrying out dangerous reactions.
  • Work in a clean and orderly manner.

Guidelines for storage, waste, spillages and emergencies

  • All packages that contain chemicals must be labelled. Use the standard hazard symbols. Solutions should also be provided with a name, date, hazard sentence and list of contents.
  • Keep the chemicals in accordance with local regulations. These are compiled in accordance with statutory regulations (PGS-15).
  • Know where you can find the eye wash, emergency shower, fire blanket, suitable fire extinguisher etc. in the event of an emergency.
  • In the event of spillages, special neutralising and absorbing packages are available. Ask the local health & safety coordinator where these materials are and how to use them.
  • Ask about the local regulations for the chemical waste. Always state the name of the substance when storing and disposing of chemical waste.

Specific guidelines for flammable substances

  • Work in the fume cupboard or otherwise with sufficient ventilation so that the concentration of the vapours is not harmful for the health and so that no danger of fire or explosion can develop.
  • Look out for spilled flammable liquids. Do not continue to walk around with contaminated clothing on.
  • In experimental rooms no more than one day's supply of flammable fluids may be present.
  • After working hours all flammable substances should be stored in a safety cabinet (fire resistant and ventilated).
  • Squeeze-bottles containing flammable substances (for example, acetone) can easily cause fire due to static electricity or a siphon effect upon heating. Limit the use of such bottles (and their contents) as much as possible.

What do I need to look out for during the storage, transport, connection and disconnection of gas cylinders?

The storage and transport of gasses inside and outside buildings is subject to strict statutory regulations. The connection and disconnection of gas cylinders are hazardous tasks.

Storage of gas cylinders

  • The storage of full and empty gas cylinders not in use must take place outside of the building in a dedicated storage area.
  • Also gas cylinders in use should, in principle, be kept outside of the building. If that is not possible then solutions must be found that are in accordance with the statutory regulations (for example, placing in safety cupboards). 
  • The gas cylinder must have a protective cap to prevent the main valve from being damaged or broken off.
  • The reduction valve should always be removed. 
  • Gas cylinders must be stored separately in the storage area according to the type of gas contained. 
  • Ensure that the gas cylinders cannot fall over (fix with a chain). 
  • Empty gas cylinders must be kept separate from full ones and be clearly labelled as ‘empty’. They must be handled with the same caution as full cylinders. 

Transport of gas cylinders

  • Only experts or sufficiently trained persons may transport gas cylinders. 
  • Gas cylinders must be transported with a gas cylinder truck; the gas cylinders must be firmly attached to this. 
  • Only transport gas cylinders with a protective cap. 
  • Never pick up or hoist a gas cylinder by its cap. The cap is meant to protect the vulnerable main valve and can come loose. 
  • If gas cylinders need to be hoisted then do this in a container.
  • Do not throw or knock gas cylinders and do not roll them either. Falling, rolling and knocking can damage the main valve or cause it to leak. This also applies to the transport of cold gas cylinders due to the cold brittleness of the material. 
  • Protect gas cylinders from falling over (use a chain). 
  • The transport of gas cylinders in a private car is forbidden.

Connecting and disconnecting gas cylinders


connecting reducing valve disconnecting reducing valve
  1. Attach the cylinder with a stirrup or chain.
  2. Remove the protective cap if necessary.
  3. Connect the reducing valve. Make sure it is the correct type and check that the sealing ring is not damaged.
  4. Close all other valves (reducing valve and/or needle valve) before you open the cylinder.
  5. Open the cylinder slowly (to protect the membrane).
  6. Then open the other valve(s).
  1. Close the main valve of the cylinder.
  2. Close the reducing valve.
  3. Release the pressure from the pipes (open the needle valve and then close this again).
  4. Disconnect the reducing valve (needle valve)
    (please note: do not allow corrosive, flammable and toxic gasses to escape into the work area).
  5. Put the protective cap on the cylinder.
  6. Take the cylinder away.

Gas cylinders

opening gas cylinder

closing gas cylinder

Make sure the reducing valve and needle valve are closed.

Release the pressure from the reducing valve and pipes (please note: do not allow corrosive, flammable and toxic gasses to escape into the work area)

  1. main valve (slowly to protect the membrane)
  2. reducing valve
  3. needle valve
  1. main valve (hand tight is tight enough)
  2. reducing valve
  3. needle valve


  • A cap nut may be attached to the valve connection; make sure the valve is properly closed before removing the cap nut. Keep the cap nut safe and put this back on again later.
  • Nuts and swivels with a left-handed thread (for example, in the case of oxygen) always have notches on the side. 
  • The following always applies when connecting and disconnecting a gas cylinder:
    • only use original and undamaged packing rings suitable for the type of gas; in the case of aggressive gasses replace the packing ring with each change of cylinder;
    • the connection must be clean and oil free (oxygen + fattiness = fire);
    • never flush through with hydrogen or acetylene as it may cause self-combustion;
    • do not use copper, copper alloy or silver solder with acetylene; acetylene forms acetylide with these (explosive in dry form);
    • avoid leakages! Always check valves using soap suds or an electronic leak detector; never use a flame. 
  • Use only an original and good-fitting key for opening and closing the valve. The key must always be kept with the gas cylinder. 
  • In the case of flammable gasses place flame extinguishers in the pipe. Repairing gas cylinder valves yourself is prohibited.

What do I need to look out for when working with hazardous gasses?

Gasses must be handled with care. Special rules apply to toxic and flammable gasses. Mixing requires permission.

  • For the ordering, storage and working with toxic and/or flammable gasses follow the locally applicable procedures. 
  • Leave the connection and disconnection of gas cylinders to qualified persons.
  • Before using a gas read its safety information sheet (MSDS). 
  • Be certain about the content of a gas cylinder. Only the embossed detail in the head of the cylinder provides absolute certainty about the contents. Therefore do not depend on the colour of the cylinder and the thread of the valve. 
  • Never allow the gas cylinders to heat up. The maximum safe cylinder temperature is 50ºC. 
  • Keep a safe distance from the dial of the manometers. In the case of a leaking Bourdon tube the dial and glass of the manometer can fly off.
  • Prevent internal contamination of the cylinders by:
    • using non-return valves if necessary;
    • always leaving a small residual pressure in the cylinder;
    • closing the valve after use. Follow the guideline (see the frame on this page) for the opening and closing of gas cylinders.
  • If you suspect that the cylinder is contaminated warn the person responsible for gasses or the supplier. 
  • Immediately transport empty cylinders to the gas cylinder storage facility and affix a sign with the word 'empty' to the cylinder.
  • You may not fill gas cylinders yourself.

Toxic and/or flammable gasses

  • Consider the installation of a gas leakage detection system in the working space/ and or storage space. This is required if the threshold limit value (TLV) can be exceeded. Ask your health & safety coordinator about this.
  • Draw up a plan in advance for the safe use of the gas together with the person in charge or your health & safety coordinator. The gas may never flow freely into the room.
  • Assume the most dangerous situation when drawing up safety measures, for example, a serious leakage occurs (torn main pipe) and the main valve can no longer be closed. 
  • Position the detectors low in the room for heavy gasses and high for light gasses.
  • Some gasses are hardly toxic but can yield extremely poisonous products in the event of a fire, naked flame or (over)heating. Examples: the isolation gas SF6and the cooling agent freon. Bear this in mind.
  • For hazardous gasses draw up an emergency plan together with the safety officer or the health & safety coordinator. The measures should be known to colleagues in the vicinity. 

Self-composed mixed gasses

  • In exceptional cases you may compose your own mixed gasses. You must first of all gain permission from the responsible safety officer. 
  • Keep the gas pressure in the cylinder as low as possible.
  • Never use a randomly chosen (used) gas cylinder but always a new one.
  • Label the cylinder, even if it is only to be used briefly. Never change anything to the embossed data of the cylinder. Ask the responsible person how to deal with such information.

Lecture bottles

  • The general rules for gas cylinders also apply here. However, these cylinders may be used outside of a gas cylinder storage facility. See also 'toxic and/or flammable gasses'. 
  • Lecture bottles not in use should always be kept in a gas cylinder storage facility. 


  • Gas cylinders must be inspected on a regular basis. See the leaflet (in Dutch only) re-inspection periods per type of gas.
  • All appendages (regulators, valves, pipes) must be inspected regularly (preferably annually).


The Environmental Management Act prohibits the storage and use of gas cylinders for which the inspection period has lapsed. When ordering gas cylinders (so lecture bottles as well) please bear in mind that the content must be used and disposed off within the re-inspection period.

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