Cleaning the cleanroom: Do I use the triple bucket system?

BY DR TIM SANDLE | PHARMACEUTICAL MICROBIOLOGY AND CONTAMINATION CONTROL EXPERT

19th September

 

With dry methods being ineffective1, the double or triple bucket system should be deployed when cleaning and disinfecting cleanrooms. 

 

It has been demonstrated that the triple-bucket system, which uses two buckets of disinfectant or detergent and one empty bucket, improves the effectiveness of the cleaning and disinfection of a cleanroom (as well as healthcare facilities2). This is further enhanced with the use of a mechanical wringer3.

 

It is therefore recommended that use of a triple bucket system should be considered in high grade cleanrooms (EU GMP Grade A and B, as well as C areas containing isolators). In this article, the case for the triple bucket system is set out. 

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The US Centers for Disease Control and Prevention (CDC) recommends the three bucket system for disinfection4 and the use of the two bucket system for cleaning only. 

 

The objectives of cleaning and disinfection are to achieve specified microbial cleanliness levels as well as minimising residuals (where residuals can pose cross-contamination risks to product as well as functioning to inactivate other cleaning or disinfection agents). 

 

The importance of cleaning before disinfection must not be overlooked5. Too often a fear of contamination encourages the use of powerful disinfectants for the elimination of real or imagined surface contamination levels. Not only do these agents offer false assurance against contamination, but their disinfection potential also cannot be achieved without the prior removal of organic soil.

 

 

 

Approaching cleaning and disinfection

 

When approaching cleaning and disinfection, it is important that cleaning personnel are well-trained and cognizant of the objectives. Drawing on the following training approach commonly used in hospitals can be useful6:

 

  • Step 1 (LOOK) describes a visual assessment of the area to be cleaned
  • Step 2 (PLAN) argues why the bed space needs preparation before cleaning
  • Step 3 (CLEAN) covers surface cleaning/decontamination
  • Step 4 (DRY) is the final stage whereby surfaces are allowed to dry

 

However, there are further nuances to develop effective cleaning. One important aspect is with the number of buckets required for the cleaning and disinfection process.

 

 

 

Single bucket

 

The simplest system is a mop and bucket containing the cleaning solution to be used. The mop is dipped into the solution and used to apply the solution to the surface. The mop is dipped repeatedly into the solution leading to contamination of the solution and poor efficiency. This system may be acceptable in a domestic setting but is not appropriate when trying to achieve a GMP standard of cleanliness.

 

The relative weakness of the single-bucket system was demonstrated in a 1968 study which explored what properties are necessary in order to constitute an effective disinfectant-detergent for hospital floors. It showed the microbial count reductions were in the high 90% range when the double bucket system was used compared with the 70-80% range with the single bucket method7. A second study also put the microbial count reduction from the single bucket method in the 70% range8.

 

 

 

Double bucket

 

An improvement on this is a ‘double bucket system’. This consists of a bucket containing the cleaning solution and a second bucket containing clean water with a wringer above. The mop is dipped into the cleaning solution and applied to the surface. 

 

Before dipping into the solution again, the mop is rinsed in clean water and wrung out. Any dirt picked up by the mop will end up in water rather than in the cleaning solution. The water will become contaminated leading to lower efficiency when rinsing the mop. According to Halls, the method can be summarised as9:

 

1.    Dip the mop into the disinfectant
2.    Mop the floor (preferably at a set number of square metres per ‘dipping’)*
3.    Dip the mop into a bucket of water
4.    Rinse the excess water from the mop head back into the bucket of water. It is important to avoid carrying any excess water back into the disinfectant. This could not only transfer contamination, but also dilute the disinfectant
5.    Dip the mop into the disinfectant
6.    Repeat

Image: Double bucket system (Image by Tim Sandle)

*For example, a qualification may show that an area of 10 square metres (~120 square feet) represents the maximum that can be mopped before re-dipping the mop in the solution. In a second example, it may be that a cleaning or disinfection solution needs to be changed after cleaning an area of 22 square metres (~240 square feet).

 

 

Triple bucket

 

A further improvement is the ‘triple bucket system’. In this system, the wringer is above a third bucket10. This is initially empty and will collect waste. This is initially empty and will collect waste. After the mop has been used to apply solution to a surface, it is wrung out over the empty bucket, rinsed in the clean water and wrung out again. The mop may then be reloaded with cleaning solution.

Image: Triple bucket system (Image by Tim Sandle)

This system minimises the contamination of both the clean water and cleaning solution, therefore improving efficacy of the cleaning process.

 

Again drawing on Halls, the method can be summarised as:

 

1.    Dip the mop into the disinfectant
2.    Mop the floor
3.    Dip the mop into a bucket of water
4.    Rinse the excess water off the mop head back into a third, empty bucket
5.    Dip the mop into the disinfectant
6.    Repeat


The triple bucket system can also be represented by the following diagram:

 

Image: The Triple Bucket Process (Image by Tim Sandle)

 

 

With all mopping techniques, it is important not to ‘double dip’ mops (dip the mop only once in the cleaning solution - dipping it multiple times may re-contaminate it).

 

 

Limitations

 

Neither the double nor triple bucket system removes disinfectant or detergent residues from the surfaces. For this, an additional step is required either using sterile water or 70% IPA.

 

 

Commercial systems

 

Commercial systems are available that include buckets, wringers and mops transported on a trolley. Both double and triple bucket systems can be sourced. The design of mop varies according to the classification of cleanroom and the type of surface it is to be used for. Not all mops and wipes are equally effective and the durability of some materials are adversely affected by disinfectants like hypochlorite11. In order to improve application, the time to mop each room, floor drying time and the amount of disinfectant used should be understood and reproducible12. 

Attention must also be paid to ergonomics. If cleaning personnel cannot move and utilise buckets or carts correctly, they will fail to perform their cleaning and disinfection activities adequately13.

 

 

Alternatives

 

Sterile mop wipes impregnated with various cleaning and disinfectant agents are also available. Care must be taken to ensure that the correct quantity of detergent or disinfectant can be released from the mop wipe14.

 

 

Summary

 

This article has assessed approaches to effective cleanroom cleaning, drawing upon some approaches common to healthcare facilities. The article indicates that wet mopping procedure, using the triple bucket system, as the most effective. 

References

 

1.    White, L. F., Dancer, S. J., and Robertson, C. (2007) A microbiological evaluation of hospital cleaning methods. International Journal of Environmental Health Research, 17(4): 285–295
2.    Smith, J. (1999) The effect of different cleaning methods on environmental monitoring, National QA Symposium, Grantham (personal notes).
3.    Singh, K., Siddharth, V., Singh, G. (2021) Mechanized laundering of mops for floor cleaning can reduce infection transmission through hospital floor, Indian Journal of Medical Microbiology, 39 (2): 224-227
4.    Anon. (2024) Best Practices for Environmental Cleaning  in Healthcare Facilities: in Resource-Limited Settings, 2nd edition, Cape Town, South Africa: Infection Control Africa Network; 2019. Available at: https://www.cdc.gov/hai/prevent/resource-limited/index.html and http://www.icanetwork.co.za/icanguideline2019/ 
5.    Dancer, S.J. (2011) Hospital cleaning in the 21st century. Eur J Clin Microbiol Infect Dis 30: 1473–1481
6.    Dancer, S. and Kramer, A. (2019) Four steps to clean hospitals: LOOK, PLAN, CLEAN and DRY, Journal of Hospital Infection, 103 (1): e1-e8
7.    Litsky, B.Y. and Litsky, W. (1968) Investigations on decontamination of hospital surfaces by the use of disinfectant-detergents. American Journal of Public Health and the Nations Health, 58(3): 534-543.
8.    Schmidt EA, Coleman DL, Mallison GF (1984) Improved system for floor cleaning in health care facilities. Appl Environ Microbiol 47:. https://doi.org/10.1128/aem.47.5.942-946.1984 
9.    Halls, N. Perspective in cleaning: How do you mop your floors? In Sandle, T. (Ed.) Pharmig Reviews No. 1: Current perspectives on environmental monitoring, Pharmig, UK, pp39-40
10.    Sandle, T. (2016). The CDC Handbook: A Guide to Cleaning and Disinfecting Cleanrooms, 2nd Edition, Grosvenor House Publishing: Surrey, UK
11.    Lehman D. (2004) Microfibers, macro benefits: health care facilities discover microfiber mops and cloths, Health Facility Manage. January 2004, 42-44
12.    Vittoria, A., Fernandez, M., Walker, M. and Bergdall, V. (2022) Comparison of Floor Cleaning and Disinfection Processes in a Research Animal Facility. Journal of the American Association for Laboratory Animal Science, JAALAS. 61. DOI: 10.30802/AALAS-JAALAS-22-000042
13.    Irwin, C. B., Farfan, R. A., and Conner, C. P. (2012). Physiological Impact of Hospital Cleaning Carts on Cleaning Staff. Proceedings of the Human Factors and Ergonomics Society Annual Meeting, 56(1), 1937-1939
14.    Dancer SJ. (2023) Hospital cleaning: past, present, and future. Antimicrob Resist Infect Control. 12(1):80. doi: 10.1186/s13756-023-01275-3

 

 

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