How Clean is 'Nano Clean' ?
We think of 'Nano Clean' in terms of sub-micron, nano-particle density.
'Nano' is the SI unit of measurement for 1x10-9
1nm (nanometre) is 1 billionth of a metre, that is; 0.001um, 0.000001mm, 0.000000001m.
With the naked eye, the smallest particles we can see are around 30,000nm, that is 30um, 0.03mm, 0.00003m.
In BS EN ISO 14644-1:2015 Cleanrooms and associated controlled environments Part 1: Classification of air cleanliness by particle concentration [Table 1] we see cleanliness classification limits for sub-micron (nano) particles/m3 in the range of equal to or greater than; 0.1um (100nm), 0.2um (200nm), 0.3um (300nm), 0.5um (500nm).
Particles of Concern
In Cleanrooms and Controlled Environments the particles of concern are random shapes and sizes, comprising; skin particles shed by staff, fibres from fabrics and process generated particles from machinery and equipment.
Properly fitted and tested terminal HEPA filters will eliminated virtually all 500nm particulate for the incoming airflow, particles of concern are generated in the Clean Environment by people and process.
Like pebbles on a beach, airborne particles are not a regular shape or size.
But for this exercise, let us imagine they are, think of them as tiny 500nm diameter nano-spheres.
At ISO Class 5 the limit for particles =>500nm (0.5um) is 3,520/m3, at ISO Class 7 it is 352,000/m3.
Considering the retired American Federal Standard AFS 209, ISO Class 5 and ISO Class 7 were comparible to Class 100 and Class 10,000 with 100 and 10,000 particles =>500nm (0.5um)/ft3 respectively.
=>500nm particles are of concern in life science applications as they can host bacteria.
A Linear Perspective
If we travelled on the Orient Express from Paris to Budapest, that’s a distance of approximately 1,200km, or 1,200,000m.
According to Google, the sleepers on European railway tracks are spaced about 600mm (0.6m) apart.
By my rudimentary calculation, that means there are about 2 million sleepers on the line from Paris to Budapest.
If we line up our imaginary 500nm nano-spheres next to each other, we will need 2 million of them to make a 1m long line!
That’s the same number of 500nm nano-spheres in 1m as there are sleepers on the railway line from Budapest to Paris!
But Cleanroom Standards Consider Particles per Unit Volume
In our ISO Class 5 laminar flow workstation, we have a limit of 3,520 particles of =>500nm/m3.
So, if our randomly spaced nano-particles would oblige and let us distribute them uniformly in the 1m3 (1000 litre) volume, we would have maximum 1 particle per 284ml.
At ISO Class 5, we are allowed just 1.2 nano-particles of 500nm in an empty 330ml fizzy drink can!
At ISO Class 7 there would be 1 uniformly distributed 500nm nano-particle per 2.8ml, giving a maximum limit of 118 in an empty 330ml fizzy drink can.
Taking the Pea!
Google says that on average peas are between 4.0 and 7.5mm in diameter.
A humble 5mm diameter pea is 10,000 times larger than our 500nm critical particle.
A regular 40’ shipping container has a volume of 67.7m3.
As a 500nm ISO Class 7 visualisation, a 40' sea container would hold a maximum of eight 1.2kg bags of peas.
Enough for 118 average portions.
As a 500nm ISO Class 5 visualisation, a regular 40’ sea container would contain a maximum of 238 peas.
That’s about an average 80g portion!
I thought of using baked beans as the visual reference for this blog, but decided it might be too saucy!
Peas feal free to share this; clean, green, healthy eating information ;-)