Safety Services


Dangerous Substances and Explosive Atmospheres Regulations (DSEAR​)

Dangerous substances are any substances used or present at work that could, if not properly controlled, cause harm to people as a result of a fire or explosion or corrosion of metal. ​

What is DSEAR?

DSEAR requires employers to control the risks to safety from fire, explosions and substances corrosive to metals. You must know when you are working with dangerous substances and how these substances are dangerous and then those risk must be controlled.​

On this page 

​Ways to check if DSEAR will apply

  1. Check the history of the substance
    Almost all organic dusts (Cellulose - C6H10O5) and a large number of metals dusts (aluminium, titanium and magnesium) can form explosive atmospheres.
    The SDS for the solid metal may not have the risk but one for the powder or dust should.​
  2. Check if the flashpoint is below 32°C – a hot summer day​
    Once you know if there is the possibility of fire and explosion a DSEAR based risk analysis needs to be carried out. ​

​Check whether the substances have been classified under the Classification, Labelling and Packaging Regulation (CLP) as: explosive, oxidising, extremely flammable, highly​ flammable, flammable, compressed gas or corrosive​?

Risk assessment 

A suitable and sufficient DSEAR risk assessment will require expertise from outside UCL. A competent person must be consulted on the control measures regarding the zoning required for the site and matters such as ATEX and IECEx electrics (gas and dustproof).

​A DSEAR based risk analysis is the first step before a full DSEAR assessment and checks occur. In order to see if an explosive atmosphere is likely to be created and whether further controlled measures need to be considered. This is someone who understands the hazards and the risk they present for the task being undertaken.​

In most cases, the Principal Investigator (PI) of a project either working with or producing the dangerous substances or explosive atmospheres will have this knowledge (what substances are going to be used, how much, the way it is going to be used and what can wrong).

​UCL Safety Services does not have an appointed person for carrying out this type of risk assessment. UCL Safety Services and UCL Estates can work with PI to ensure that suitable control measures are in place once it has been established that an explosive atmosphere is going to be created or is likely to be created.​

DSEAR based analysis ​

  1. ​List the product or substance that you have identified as dangerous/explosive (this includes all dangerous/explosive substances that are handled, stored or produced)​
  2. Write out each step of the work system/activity​
    - Highlight all sources of ignition​
    - Highlight where failure could result in a fire or explosion, gas escape, mixture of fuel and oxygen, other loss of containment​
  3. Calculate whether an explosive atmosphere can form. These are calculations based on the substance and the site
  4. Confirm actions have been taken to minimise the likelihood of a fire or explosion from happening:
  • Minimum quantities are being used / all scale-up experiments have been reassessed​
  • Additional controls are in place to prevent /minimise the release of dangerous substances (intentional and unintentional)​
  • Control measures have been taken to prevent release at source including storage / and transport to an experimental area​
  • Specific controls are in place to prevent an explosive atmosphere from being reached e.g. forced ventilation, an experiment carried in an inert atmosphere​
  • Controls are in place to ensure waste dangerous substances are collected, contained and removed safely​
  • Controls are in place to control the environmental conditions to lower the risk such as temperature, pressure or humidity​

Once this is completed, you can assess whether the control measures in place are sufficient or whether a DSEAR expert needs to be consulted

DSEAR calculations

Air density (ρ) = 

absolute pressure (ϸ)​
specific gas constant for dry air (R) X absolute temperature (T)

Example 1
Acetone in a room 5 by 7 by 3 meters
Molecular weight (MW) 58.1g /mol, Liquid density 0.785g/mol  
Lower Explosive Limit (LEL) 2.5%v/v​

1. Calculate the vapour densityMW / Constant 1
= 58.1/28.96 = 2.01g/mol (twice as heavy as air, will sink)​

2. Calculate the relative density (20°C and 1013hPa)

MW x Constant 2
= 58.1 x 0.04179 = 2.43​ 
3. Convert the Lower Explosive Limit (LEL) to g/m3    MW x (LEL / Constant 3)     
= 58.1 x (2.5/2.4) = 60.52g/m3​
4. Calculate room volume Length x Height x Weight  
= 5 x7 x 3 = 105m3​
5. Calculate the maximum spillvolume room volume x (LEL g/m3 / liquid density) = 105 x (60.52/0.785) = 8095ml or 8.095l (assuming total dispersion)​. 

Example 2

Ethanol in a room 3 by 3 by 3 meters
Molecular weight(MW) 46.1g /mol, Liquid density 0.785g/mol 
Lower Explosive Limit (LEL) 3.1%v/v​

​Calculate the vapour densityMW / Constant 1 = 46.1/28.96 = 1.59g/mol (twice as heavy as air, will sink)​
Calculate the relative density (20°C and 1013hPa)MW x Constant 2 = 46.1 x 0.04179 = 1.93​
Convert the Lower Explosive Limit (LEL) to g/m3MW x (LEL / Constant 3) = 46.1 x (3.1/2.4) = 59.55g/m3​
Calculate room volume Length x Height x Weight = 3 x 3 x 3= 27m3
Calculate the maximum spill volumeroom volume x (LEL g/m3 / liquid density) = 27 x (59.55/ 0.785) = 2048ml or 2.048l (assuming total dispersion)

UCL generic control measures for dangerous substances​

​UCL requires the following control measures to be implemented for all flammable or explosive (dangerous) substances on a UCL site, even if an explosive atmosphere is unlikely.​

Maximum limits for dangerous substances held by a department will depend on a number of factors such as:

  • What the dangerous substance is
  • How long it will be stored on-site
  • Use​
  • Other risk factors present by the substance​

​UCL has the following guidance and recommends that deviation from this guidance is fully risk assessed and approved by the Head of the Department:

  1. ​More than 500ml of flammable and highly flammable substances are stored in fire-resistant containers​
  2. Maximum of 50 litres per lab /workspace​
  3. When it has been agreed amounts above 50 litres are to be stored (usually storage only) this will be stored in appropriate flammable stores – meets BS EN14470-1​
  4. All areas storing liquids are bunded to take 110% of the largest container or​
  5. All areas storing liquids are bunded to take 25% of the liquid stored.​Incompatible substances are stored apart​
  6. Appropriate manual handling aids are in place to assist with the transport of the substances, e.g. Winchester carriers and trolleys for gas cylinders​
  7. Emergency plans are prepared and communicated to all relevant parties​:
  • Location, contents, use and limitation of spill kits​
  • Use of forced ventilation to clear a dangerous atmosphere​
  • Emergency switch-off for utilities, piped gas, ignition sources.
  • Quarantine procedures​

Last updated: Thursday, September 30, 2021

DSEAR work review

In most cases, any dangerous substance or explosive atmosphere will be contained at source or in purpose-built containers. However, if this is not the case and the initial review (as above) of the experiment including predicting whether an explosive atmosphere will be/could be created, a project request to Estates will be required for a specialist DSEAR engineer to review the work areas and assist in the full risk assessment. 

Raise a project request​ →