HEPA Negative Pressure Units don't really work
HEPA stands for High Extract Particulate Arrest and Negative Pressure Units are basically an air mover fitted with HEPA. They have been used for many years in the asbestos industry to control air and pressure differentials. If you have ever worked with NPUs in a dirty enclosure you will find layers of dust on the top of the machine in the morning.
Stokes law states all particles will eventually fall but due to varying weight, aerodynamics differential rates will apply.
One anyone moves in that enclosure secondary aerosolisation will occur and we start again.
The Health and Safety executive (HSE) have published papers which show evidence from their own experiments which show stratification and failures of NPUs to decontaminate air either in layers or indeed outside the pathway.
The installation of NPU's is usually within containment and this apart from cost is a maintance and long term and costly procedure
The photo at the head of the home page shows one of our experiments which shows why NPUs don't provide anywhere near what you might imagine and here we put a 500 cfm into a 1000 cfm and show after 30 minutes simple smoke let alone particulates could not be removed.
The training and products we provide allows decontamination within minutes .