Control of Substances Hazardous to Health - COSHH Level 2 (VTQ)

47 videos, 1 hour and 58 minutes

Course Content

Mixing of Chemicals

Video 17 of 47
3 min 4 sec

In the workplace, there are many very dangerous chemicals and you may think that in your workplace there are no chemicals that could pose a significant risk but it may be that the risk is when you mix two chemicals together. 

These reactions will depend on the substances, some chemicals used in industry can become explosive, corrosive or they then become a different chemical which was not thought of in a risk assessment. Extreme care must be taken to ensure that chemicals are not mixed on any scale as the resulting mixture may be very harmful to health. 

There was a case where an office cleaner mixed two normal cleaning chemicals together both bleach-based cleaners. 

What happens when you mix these substances is that they react and create a chemical reaction that produced Chlorine Gas, which is a gas that was similar to what was used in World War One. The cleaner in this case died. 

What happened, in this case, is hard to say exactly, but one was an acid-base and the other mainly sodium hypochlorite. The data sheets show that you need to take precautions against mixing these two chemicals because it might produce chlorine gas. Chlorine is a dangerous chemical and can also be found in different forms in the leisure industry for use in swimming pools.

Chlorine gas exposure, even at low levels, almost always irritates the mucous membranes (eyes, throat, and nose), and causes coughing and breathing problems. It also causes burning, watery eyes, and a runny nose.   Higher levels of exposure can cause chest pain, more severe breathing difficulties, vomiting, pneumonia, and fluid in the lungs. 

Very high levels can cause death.  Chlorine can be absorbed through the skin, resulting in pain, inflammation, swelling, and blistering. Hydrochloric acid also causes burns to the skin, eyes, nose, throat, mouth and lungs. Accidents like this where someone dies are rare and will depend on many factors including ventilation and the environment but accidents can happen so care needs to be taken and it may that you cause a dangerous situation for someone else to enter. In milder exposures, the person may be affected by eye problems, breathing difficulties, skin disorders, headaches, nausea and sickness. 

With cleaning products, some general advice is to not mix bleach and ammonia. Do not mix bleach and acids. Do not use two drain cleaners together, or one right after the other. 

We have looked mainly here at mixing cleaning chemicals but many other chemicals react badly when mixed and we cannot cover them all in this video.

Accidents like this can be avoided by understanding that you cannot mix chemicals without first checking that the two substances are stable and do not react. If in any doubt, do not mix them and consult the safety data sheet for both chemicals, contact your manager or the manufacturers of the chemicals.