Arguably the most important part of the whole RPE process is fit testing, as this ensures that the apparatus works well and keeps the dangerous substances away from the mouth and, ultimately, out of the body.

The HSE states that "a major cause of leaks is poor fit", adding that "tight-fitting facepieces need to fit the wearer’s face to be effective".

If a mask is too loose this can't happen and firms need to be proficient in ensuring their employees have the right equipment and that it fits well.

Essentially, the process is all about choice. Have a range available, in different sizes, and simply ask which one feels the best and also ensure the mask is tight, without being overly so for the wearer.

From then on, it's about making sure this piece of equipment is available for the employee in question.

The HSE advises: "If an employee wears more than one type of tight-fitting facepiece, then each type of facepiece should be fit tested."

In terms of who needs to carry out this procedure, it needs to be done by a trained employee, who is given the designated job by the company.

The British Safety Industry Federation has a process by which workers can become accredited and, given the importance of the job, this qualification needs to be taken seriously.

"RPE fit testing should be conducted by a competent person - you should take steps to ensure that person who carries out the fit test is appropriately trained, qualified and experienced, and is provided with appropriate information to undertake each particular task," the HSE states.