However, they get confused by the assessment process and often use inadequate assessment techniques. This usually means that the control measures they decide on during the assessment process aren't sufficient to control the risk presented by the hazard.

Here are the top 5 COSHH assessment mistakes you may be making:

Allowing untrained, incompetent staff to conduct your COSHH assessment
This is an important question to ask yourself, whether you're working with a high or low-risk situation. It doesn't matter how much of an enthusiast you are, if you don't have the right training and experience with specific processes, your assessments are going to be incomplete.
It's very easy for inexperienced assessors to miss critical points, endangering your workplace and the rest of your employees due to uncontrolled risks.
The most common mistake inexperienced COSHH assessors make is concentrating on the completely wrong thing, usually because they're confused about the difference between a risk and a hazard.
This generally means the assessor concentrates on the substances instead of properly assessing the work process. An assessment should cover the task as a whole, what is used during it, how long for, and what may be created by the process.

For example:
You've just installed a new workstation for dressing aluminium castings.
You need several tools to do your task, all of them requiring an oil to ensure the blades operate as intended when dressing the surface of the casting.
The work process itself also creates hazardous substances as it is being carried out. In the form of fumes, vapours, dust, and fine-particulates made up of the oil and tiny pieces of the blades and aluminium.
Before your work can begin you need to perform a chemical risk assessment.
You choose to do a substance assessment of the oil and the hazards it presents because it's the only substance you currently know of being used for your task.
Because you lack training in a proper COSHH assessment methodology you neglect to assess the task itself, including how the oil will react as you proceed.
You also don't take into account the hazardous substances that are likely to be produced as you do your work, where they will go and how they can affect the entire workstation.

Neglecting to review your COSHH assessments, especially following workplace changes
This is potentially the most dangerous mistake you can make. Assuming that everything is as safe as it was when you conducted the assessment 18 months ago is asking for trouble.
Nothing ever stays the same.
The work process might be identical but 18 months after you installed them, the control measures may be showing signs of age. Control measures that aren't doing their job are not adequate control measures.
This is obviously a very simple example, but it's important to regularly review your COSHH assessments. And while there is no legal requirement, the HSE (us too) recommend that you review any assessment annually, at the very least.
There are other reasons to take your assessments under review, however.

Ask yourself these questions:

• Were new hazards introduced? 
• Has there been any change in the level of exposure your employee faces? 
• Have new hazards introduced new risks? 
• How likely is it that the hazard can cause harm, and what would be the severity of that harm? 
• Have any changes been made to the known hazards, and do those changes modify the likelihood, and severity, of a harmful event? 
• Are the existing control measures still adequately controlling the previously known risks? 
• How would you prioritise the new risks? 
• Does that affect your previous priority of the known risks? 
• Can you control the new risks with existing control measures? 
• If no, what control measures can you implement?

Making your COSHH assessments far too complicated
Aren't they supposed to be complicated?
No, they aren't! It's completely unnecessary to over-complicate your chemical risk assessments.
Keep in mind who will be reading it down the line. It needs to be understandable to anyone. Including anyone who might not be very clued up on the COSHH regulations or risk assessments in general.
Anyone not understanding your jargon is going to skim over it and miss the really important information.
When recording your COSHH assessments, you should be clear and concise.
There is nothing worse than seeing a group of ticked check-boxes, but no details on why they were ticked, when they ticked, or even who did the ticking!

Failing to engage your employees in your COSHH assessment and control processes
Your employees are obligated to follow the chemical safety guidelines, just like you. They hold a legal responsibility to use the control measures that you or your managers implement.
While you do, indeed, play the critical role of risk assessor, their jobs are probably more important.
Your employees spend most of their time on the shop floor, with eyes on the hazards that they work around. A very important part of COSHH safety is the reporting of incidents, near-misses or new hazards.
Your employees are the best people to spot those failures or potential new hazards because they're doing the job on a daily basis.