Is it Ok To Mix Chemicals?  (Some COSHH Risks You May Not Have Thought Of)

by Matt Besley on 25-6-2019

Chemical Mix

Allowing cleaners to mix cleaners is a game of chance.  Of course; mixing chemicals isnt always as obvoius as pouring 2 chemicals into a bucket.

Here's the why's and wherefore's and key areas you may not have considered.

Should you allow cleaners to mix chemicals?  Very definitely not.  In effect you will be making a new product with the mixture of the chemicals, and by rights you should be creating a new COSHH sheet.  Quite aside from this, the risks of mixing chemicals can have terrible consequences.  Read on to make sure you're covered.

Key areas you should watch out for:

1- Bleach (Let's start with the deadly stuff)

Cleaners often mournfully tell me that they're not allowed to use bleach, but often they are not sure why.

Mixing bleach with some acids will create chlorine (or mustard) gas - it is exceptionally dangerous and can be deadly if inhaled.

it's surprising how many people still use bleach in a mop bucket and are mixing it with other chemicals, not knowing the deadly consequences.

Key points:

  • Not everything that is bleach based says bleach on the label!  Be wary of mould killers - 
  • Consider using different chemicals in place of bleach; aside from mould and green organic growth on surfaces, there are more effective chemicals for pretty much everything else.
  • Consider banning it completely from your cleaning cupboard; or keeping it more restricted than other chemicals.

Further reading:


2 - Making Chemicals Up (and the Cleaning Cupboard)

Pay attention to where the chemicals are being diluted to ensure that the chemicals arent being mixed.  Also pay attention to spills of chemicals in the cleaning cupboard - where you are using dosing pumps, there may be drip trays.  And communal drip trays for multiple chemicals are a definite no-no (as picured in the main image!)

Key Points:

  •  Make sure your chemicals are locked away when not being used (especially where there are children or vunerable adults using the building)
  • Use dosing charts (ask us for bespoke dosing charts for your cleaning cupboards)
  • Make sure your staff are trained on diluting chemicals and COSHH


Further reading:


3 - Surface Cleaning

Consider when you are cleaning a surface that you are not using 2 products on the same surface.  Pay particular attention to where there are stains or marks and stronger products are being tried.  Ensure you always rinse between using any products very thoroughly.  Special attention should be given where you are using strong mould sprays or descaling products in washrooms.

Key points:

  • Ensure you flush the toilet before cleaning - you dont know what has been used on it before
  • Take particular care when deep cleaning especially when using mould sprays and descalers in close proximity - ensure thorough rinsing between cleaning.


Further reading:


4 - Drain Cleaning

You can get some pretty strong drain cleaning solutions that are strong acids or strong alkalis - a classic chemical mixing example is where you use one drain cleaner - before it gets to the blockage the chemical has diluted with all the water it has mixed with that is backing up; then when you add in another chemical, the solution is ready to mix and react!  

Key points:

  • Consider non-chemical drain cleaning methods where applicable like drain rods or a plunger.
  • Take particular care when you are using a 'one-shot' type product or caustic soda pearls.


Where it may be ok to mix

Sometimes you may be able to mix some chemicals.  If you are cleaning carpets etc, you can use a deodoriser in with the main chemical in the solution tank of the machine.  Always read the label, and always use with caution.

Remember; never mix chemcials - the results can be at best dangerous, at worse deadly.

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