New research from the HSE finds that non-regulation Qualitative Fit Test hoods could lead to false passes and subsequently endanger lives.


With so many different Qualitative Fit Test Kits on the market, with different colour, shape and size hoods – what’s the difference, and does it matter?

Is it all in the name of fashion, or can the size of your hood really affect the Fit Test?

Alison Bowry from the Health & Safety Executive wanted to know just that and undertook a series of tests to find out how the shape and size of a Fit Test kit hood could affect the volume within the hood space and the subsequent concentration of aerosol within it during a Qualitative Fit Test.

While the HSE’s OC 282/28 and the ANSI Z88.10:2010 recommend that Qualitative Fit Test hoods be 12” in diameter, 14” tall, form a cylindrical shape and have an internal hood space volume of 20l, not all Fit Test kit hoods measure up to spec.


The Preparation

Before any testing could begin, the researchers sourced 10 commonly available Qualitative Fit Test kits and found that among those 10 kits were three different designs of hood.

However, before testing could begin it was noted that varying the assembly of the same make/model of hood could potentially have an impact on the hood’s capacity.

As manufacturer’s instructions are not always clear on construction (for example should a hood be left flat or shaped?), and to account for user error, testing was done on different configurations of each model to assess whether or not it would affect the results.


The Method

After the hoods and variations of assembly were agreed, the volume of empty space for each was calculated, taking into account the volume of a standard mannequin’s head.

From there, the researchers performed repeat ‘Fit Tests’ on the mannequin using the Qualitative method of spraying Bitrex aerosol into the hood. For each configuration of hood, the tester gave 10 squirts to introduce the test and then a further 5 squirts every 30 seconds for 7 minutes.

Unlike a real Fit Test, no attempt however was made to simulate head movement or other exercises.

Before, during and after the ‘Fit Tests’, the particles within the hoods were measured using a PortaCount machine to assess how the aerosol dispersion of aerosol


The Results

While the standard 20l hood read 65,782 particles/cm3 during the ‘Fit Test’, the largest hood only read 18,582 particles/cm3 – more than a 3.5x difference.

Looking at the results, it seems that the larger volume the hood, the more dispersed the particles and subsequently the weaker the concentration of the aerosol within it.

Bowry concludes: “There is a general trend in reduction of concentration of aerosol with increasing hood size. A lower concentration of aerosol in the hood may lead to a fit test that is not as sensitive as required.”

While a reduction in sensitivity may not sound like a big problem, we must remember that RPE is used as the last line of defence against respiratory hazards in the workplace (HSG53 22). Respiratory hazards that cause around 12,000 deaths every year in the UK alone. If there is even a chance that we accidentally pass someone on a respirator mask that is not suitable for them, we could literally be handing them a death sentence.


The Application

When undertaking Qualitative Fit Testing, you must ensure you do all you can to minimise risk of false passes, including the use of regulation sized hoods.

For a fully compliant Fit Test solution, choose the Full Support Qualitative Fit Test Kit.

  • HSE regulation sized hood
  • Individual ampoule solutions to minimise spillages
  • Illustrated instructions for easy-use


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