How to test your Deprox


The Deprox settings can be simply tested as follows:

  1. There are a number of concealed buttons on the LCD panel of the Deprox unit. These are  visible as slight blisters in the plastic film to the right of the “START CYCLE” button.
  2. Pressing and holding buttons F3 and F4 simultaneously for 10 seconds will bring up the Delta RH setting on the LCD display, e.g “delta RH 10%”
  3. Pressing the “START CYCLE” button will take the machine out of “Menu” mode and back to standard operation mode.

Changing the RH setting changes the efficacy of the process. The efficacy is proportional to the H2O2 concentration, which is in turn proportional to the RH setting. The test data that Hygiene Solutions include in their tender submissions (see  TNO Report ) are for machines running at delta RH40. The log 6 efficacy claims for Deprox are based only on this data.

However, at delta RH40, the level of H2O2 and other chemicals in the air at the end of the process is perhaps 20 or 30 times the legal limit – even after the 45 minute “deactivation cycle”.  Also, except in the very driest climates, heavy condensation is formed. Consequently all Deprox units have been turned down to RH settings of between 5% and 15%. (For example, the 2 machines at Westmead Hospital in Sydney are set at 10%. The units at the Luton and Dunstable Hospital are set at 5% etc…) The efficacy is consequently greatly reduced, to between log 0.2 and log 2.

It should be pointed out that the Deprox machine has NO MEANS WHATEVER of monitoring the deactivation process. The green light is simply on a 45 minute timer, and will illuminate at this time regardless of the level of gas in the room.

Hydrogen peroxide gas detectors are expensive to buy, but can be rented at very reasonable rates from Drager UK.  The best detector for this application is the Drager X-am 5100. The contact number for gas detection enquiries is 01670 352891.

Note: Do NOT rely on on gas detectors supplied from Hygiene Solutions – these are calibrated to show only a fraction of the real gas level! This can very easily be demonstrated by using a HS supplied unit and a rented Drager unit side by side.


We can see from the graph above the huge reduction in both H2O2 concentration and  duration between Deprox settings of  RH40% and RH5%. For technical reasons explained in  “Deprox and the Emperor’s New Clothes”  at RH5% the Deprox only emits a single pulse of vapour, rather than emitting at 5 to 10  minute intervals as it is designed to do. The efficacy is approximately proportional to the area under the graph, so it is obvious that the reduction in efficacy is not 8 fold as we might calculate, but more like 100 fold.

Hygiene Solutions keep a couple of “demo” machines at their depots both in the UK and Australia that are set to a delta RH of 30%. These are used to “demonstrate” to new or skeptical customers that the process is efficacious. As the H2O2 has little odour, the residual air quality issue is not apparent unless an H2O2 meter is used.

For full details on the delta RH setting deception, and its consequences, see “Deprox and the Emperor’s New Clothes” 

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