A high-pressure cleaner (or Kärcher) is a cleaning device that propels water at high pressure.

pressure washer karcher

Summary

1 story
2 Operation
3 Health risks
3.1 Importance of the quality of the water used
3.2 Experimental studies.

History

The high pressure cleaner was not invented by Alfred Kärcher (who had known the steam cleaners of the American army during the occupation of Germany); he simply improved them by adding hot water for better cleaning result.

Since the end of the twentieth century, the use of high-pressure cleaners has become very common in many work environments2 (e.g. farms and farms likely to include zoonotic pathogens (i.e. capable of infecting both animals and humans) 3, sewage treatment plants, some chemical factories, slaughterhouses, markets, boat fairing places (including pleasure craft), urban graffiti cleaning (usually with using toxic solvents) 4,5,6,7 or bins (including bins for condominiums, factories, community restaurants, retirement homes, etc.).

Operation

The device puts water under pressure (between 80 and 500 bars depending on the devices) in order to project it at high speed. The impact of water molecules removes “dirt”, paint, plaster, biofilm, etc. hard surfaces (floors, walls, vehicles …).

The pressurization is carried out by means of a piston pump system with inlet and outlet valves: they are generally made of brass to avoid any risk of malfunction due to oxidation. A valve ensures the safety of the pump in case of blockage of the circuit. When the lance control handle is released, a system stops the machine. The liquid supply must be greater than or equal to the flow rate of the machine, otherwise the pump may suffer from cavitation effect and degrade. In fact, the pump only serves to expel the liquid, and not to increase the flow rate of the source by suction. Associated with the production of hot water and a detergent, the high-pressure cleaner increases its capacities, especially for dissolving hydrocarbons and organic oils or greases.

To strip a substrate, sandblasting is possible.

Risk for the health

The use of Karchers has become considerably democratized. In industry and services, as in these cases, the Karcher is very often used without a protective mask, and sometimes without any protective clothing, while it is an undisputed and undisputed source of suspension or resuspension in the air of particles, microparticles and nanoparticles of physicochemical, mineral, metallic, organometallic and / or biocontaminant origins (endotoxins, bioaerosols).
Note: In agricultural, urban and industrial environments, Karcher is added to other, more chronic and “dry” sources of inhalable bioaerosols8.

There is a consensus that a karcher is a frequent source of bacterial bioaerosol production, especially when cleaning up excreta and in organic waste treatment areas, sewers, or in the presence of fomites and substrates covered with bacterial biofilm9, etc.) But few studies have looked at the acute or chronic health effects of inhaling these aerosols by the user (or other people, or exposed food products).
And the case of bacteria has been studied more than that of viruses resuspended in the air. Other biocontaminants are pathogenic prions, which the Karcher may also help to diffuse in aerosols 10. When used with detergents, disinfectants, biocides or enzymes, personnel are exposed to inhale them11. According to the study review published by Madsen & Matthiesen (2013), the health effects of residents who use them at home do not seem to have been studied or evaluated 12; furthermore, the variety of materials to be cleaned, the aeration and thermo-hygrometric conditions, and the degrees and types of “dirt” treated, strongly influence the level of pollutants and bioaerosols suspended in the air, and therefore the exposure level; this makes inter-study comparisons difficult. Madsen & Matthiesen also found no studies comparing the degree of exposure to aerosols by type of pressure washer, which they say makes it difficult to develop health recommendations2.

During the COVID-19 pandemic, and in particular during the first week of deconfinement, it was observed (in several countries including France) that slaughterhouses were part of the first clusters, and among the most important, of COVID-19 . Among the hypotheses put forward to explain this fact when the personnel of these installations are accustomed to HACCP practices and to wearing boots, gloves, gowns, etc. (but no mask), it has been suggested that the frequent use of high pressure cleaning could have favored human-to-human contagion by aerosols.

Importance of the quality of the water used

It is recommended to use clean water to avoid damaging the device. But if it is not as bacteriologically and virologically clean, this water can also be a health risk for users or people exposed to aerosols. Contaminated water will immediately produce contaminated aerosols, inhalable and / or likely to contaminate substrates cleaned or affected by fallout.
So :

an outbreak of Legionnaires’ disease has been associated with the high pressure cleaning of boats using rainwater collected on a roof and contaminated with the bacterium Legionella pneumophila.
High levels of this bacteria (endotoxin-producing) were measured in a water tank used to feed Karchers in a sugar factory, after 14 people there developed Pontiac fever (a form of Legionnaire’s disease without lung involvement. ; non-contagious and apparently transmitted exclusively by inhalation of contaminated aerosols16) . The water used contained 20,400 EU / ml but the workers’ exposure to the endotoxin secreted by the bacteria was not assessed  (the EU is a quantitative unit: EU stands for “endotoxin units per milliliter” (EU / mL); 1 EU = approximately 0.1 to 0.2 ng endotoxin / mL of solution);
This same “Pontiac fever” was also observed in a wastewater treatment plant where high pressure cleaning had been done, but it is not known whether there was a cause and effect relationship18.
Cleaning with a Karcher supplied with wastewater effluent water caused a significantly higher exposure to endotoxins than with tap water2, but it should be noted that chlorination (bleaching) of water surface kills bacteria there, but without significantly destroying certain endotoxins (for example, such endotoxins have been measured in the aerosol emitted by a humidifier in a workplace at a level of 1600 EU / ml, causing in in this case an exposure level of 1,300 to 3,900 EU / m3 in the room19.
Studies have described in so-called “potable” water endotoxin levels ranging from 6.2 to 5000 EU / ml of water 20 to 3.2 to 32000 EU / ml of water and 0.2 to 11.9 EU / ml water.
according to Madsen (2013), the endotoxin levels measured in some of them from wastewater treatment plant effluents (and even in so-called “drinking” water), can lead to significant inhalation of endotoxins when this water is used for high pressure cleaning 2. The discovery of the presence of endotoxins at worrying levels in certain drinking water was made during the use of this water in hemodialysis units22 (these endotoxins can be treated by oxidative or UV treatments. In 2003, Anderson & al. considered that “the risk of inhaling sufficient quantities of aerosolized water droplets containing enough endotoxins to harm human health has not yet been adequately quantified” , but there is ample evidence to suggest that health issues exist .

Experimental studies.

The aerosolization of particles of different sizes was measured in the case of cleaning a car door, in a first case with a nozzle spraying water under high pressure (7.3 liters of water / min ), and in a second case with a manual spray nozzle (11.8 to 15.4 liters of water / min). In the first case, a mist of micro and nanodroplets formed and persisted, still visible, several minutes after stopping the sprayer, and a great variability in aerosol emissions was observed. The first device was more water efficient but generated more particles with a diameter of less than 2 μm, potentially resulting in higher exposure to these small particles.
In an installation simulating high pressure water cleaning of surfaces such as those found in the food industry, it was demonstrated that high pressure cleaning can aerosolize and spread bacteria that was present as a biofilm ( very common case in the food industry); the bacterium used for the experiment was Pseudomonas putida (cousin of bacteria pathogenic to humans and animals, or plants, with for example Pseudomonas syringae which infects various cultivated species