How clean is your floor?
Peel-off mats and polymeric flooring help keep dust and dirt at bay but how effective are they? Tim Russell, commercial director of FMS reports on a recently completed comparative study designed to assess their particle removal properties
The transfer of viable and non-viable particles into cleanrooms, via personnel and movable equipment (trolleys or carts) is a major source of contamination. Quality assurance in the manufacture of sterile medicinal products includes the requirement for an appropriate environmental cleanliness level in the operational state, in order to minimise the risk of particulate or microbial contamination of the product or materials being handled 1.
A variety of methods are employed to minimise the number of particles entering the cleanroom. Optimised gowning procedures ensure that personnel are suitably prepared and cleanroom clothing is correctly worn and appropriate pressure cascades are in place to minimise the ingress of airborne particulates. Various types of floor covering material help minimise the transfer of particulates from personnel and movable equipment into the critical areas.
Studies have shown that polymeric flooring can reduce the microbial counts on the footware of staff and trolley wheels moving from one cleanroom to another 2,3,4. Using a selection of particle retentive coverings in conjunction with a unique technology combination of a particle counter and a CAT surface probe, tests were conducted that provided – for the first time ever – quick and real time, on-site results. Data will be presented here that demonstrates the ability of a selection of particle retentive mats to remove particles from the surface of shoes.
Particle counting
In order to count the particles on the surface of a shoe, a standard 0.3 to 10 µm, 1 CFM airborne particle counter was used with a surface particle counting probe attached. This particle counter has the benefit of an internal carbon vane pump which enables it to provide the suction required to allow the surface particle counting head to correctly function. The particle counter was set up to run a single 10-second sample; most of the particles on the surface are removed within the first five seconds. A start and stop sampling function is afforded by a start/stop button that is integrated into the surface-counting sample head. This enables the user to position the probe remotely, and start and stop the particle counter without having to move or turn around and potentially compromise the measurement.
The surface particle-counting sample head functions by using the filtered exhaust of the particle counter to blow air through all the jets in the outlet circle (shown in red in figure 1). The particles removed from the surface are then entrained in the airflow. The air is then sampled into the particle counter via the central orifice (shown in blue); the particles are then counted and sized normally. Data collected is reported as raw particle counts only; it is possible to report the data in terms of particles per cm3. In this study, the data has not normalised in any way in terms of the surface area sampled by the probe. The objective is to be able to show in relative values how much cleaner or dirtier a surface is.
The particle retentive floor coverings tested were as follows:
- Polymeric Flooring
- A standard dust mat
- Five peel-off mats from five different manufacturers
Testing was conducted in ambient conditions in an office workshop environment. All the particle retentive flooring was brand new and previously unused. The shoe used had a flat surface with no tread pattern. Each test was conducted as follows:
1. Contamination of the shoe surface by walking around a painted concrete floor, this represents the before (100%) count.
2. Six steps on each type of mat with a single shoe.
3. Step 6 is an over step on step 1.
4. A surface particle count on the sole of the shoe after each step at a different location on the shoe surface. (see Figure 2 for the surface particle count location)
5. Repeat 1-4 twice more, making a total of three test runs per mat.
The foot was pressed under full body weight adjacent to the previous step. Only the final sixth step was placed over the initial first step. The ambient particle contribution to each test remained constant. The data was then collated and the three runs were then averaged. The percentage particle retention on the shoe was then calculated as follows:
% Retention Step 1 = 1- [(Particle counts before - Particle Counts Step1)/Particle Counts Before] x 100%
The results for each particle retentive mat tested are shown graphically opposite: the y-axis represents particle retention on the shoe surface and the x-axis marks each step taken.
Discussion
Interestingly, when reviewing the graphical data, specifically with the peel-off mats, it can be seen that there is a spike in what would appear to be a steady particle count decay as each step is taken, this is most noticeable on peel-off mat 3. After investigation, it transpired that this spike correlated with the sample taken from the toe of the shoe. After the first step, 30% of the large particles and 60% of the small particles remained on the shoe. By the sixth step, between 5 % of large particles and 30% of the small particles remained on the shoe. It is also of interest that the peel-off mats’ particle removal performance is consistent.
The dust mat has the poorest performance, leaving 45% of the large particles and 60% of the small particles on the shoe after the first step.
The polymeric flooring leaves between 10% of the large particles and 20% of the small particles on the shoe after the first step and by the sixth step between 5% of the large particles and 15% of the small particles remained on the shoe.
There was no discernible adverse effect of particle removal when overstepping on any of the mats (overstepping was not performed on the dust mat).
Conclusion
From the data presented, it was clear that the polymeric flooring removes particles from the sole of a shoe very quickly. In order for a peel-off mat to match the polymeric flooring performance, at least 4-5 steps on each foot (10 in total) would need to be taken on the peel-off mat surface. A typical peel-off mat installation will afford one or two steps only.
There was a noticeable change in performance of a peel-off mat when removing particles from the toe of a shoe, it is recognised that this is a difficult area of the shoe to remove particles from as it is dependent on how the wearer of the shoe steps on the mat.
Additional studies looking at the performance of peel-off mats and polymeric flooring when contaminated would give a useful indication of ongoing performance. This will help give some understanding as to when cleaning activities should be carried out on polymeric flooring and when the peel-off mat requires changing.
Summary
The Dust Attenuation Coefficient was calculated by regressing in (counts) vs step number. The greater the dust attenuation coefficient, the more effective the mat is in removing and holding particles. The figures have been rounded to one decimal place (see table 1).
The data clearly demonstrates the need for floor contamination systems. It also clearly shows how well the polymeric flooring system works with the Facility Monitoring System in assessing contamination levels.
To show the simplicity and speed of this real time, on-site testing, FMS and Dycem would like to invite interested organisations to take part in a free testing programme. A follow-up article is planned to show the results of this programme with a view to much needed further research. If you would like to take part, please contact Tim Russell (01684576452), Alan Fisher (01179559921) or visit our websites, www.fmonsys.com and www.dycem.com for further details.
