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Anno 2020 Numero 12

Technology
December 2020

The operator's protection in phytosanitary treatments with the "category 4" cabin

The "category 4" approved cabins are an excellent alternative to individual protection devices for phytosanitary treatments, as they ensure adequate protection from pollutants, saving the operator from wearing heavy and bulky

Agricultural production, whether traditional or organic, requires pesticides to defend against the attack of pathogens. Both in liquid and powder form, phytosanitary products are usually distributed in a mixture with water through sprayers, which spread the product as an aerosol carrying the different active ingredients in the form of a suspended matter. The latter is, in case of skin contact, inhalation or ingestion to a greater or lesser extent, harmful to the operator.

Personal Protective Equipment (PPE), the operator's primary protection, is classified according to three different protection levels: Cat. I, suitable for low physical risk conditions; Cat. II, suitable for higher risk levels than Cat. I, but not high; Cat. III, designed to protect the operator from severe and/or fatal risks.

In addition to PPE, protection from the chemical risk of plant protection products in agriculture may also be ensured through specific filtration devices fitted in some tractor cabins. These cabins are homologated "category 4" approved, requiring the use of activated carbon filters. In this case, if adequately approved according to the regulations in force, these cabins are an excellent alternative to conventional PPE (masks, gloves, boots, overalls).

 

Personal Protective Equipment

Even though plant protection products' active ingredients are particularly dangerous in case of skin contact, the possible inhalation damage and the resulting risk of intoxication should not be underestimated. Airway protection devices can be individual, such as masks, semi-masks, and air-conditioned and naturally filtered helmets, individually worn by the operator. Although they cause a certain amount of movement obstruction and poor visibility, they are essential in some situations, such as when treating with shoulder sprayers. They use different filtering systems in terms of type and operation, physically and/or chemically. In the latter case, the filtering takes place through a chemical reaction between the harmful substance and those contained in the filter in order to block its diffusion.

 

Category 4 cabins

In order to be “category 4" approved, the cabin must comply with specific requirements established by UNI-EN 15695-1:2018.

In practice, the cabin must be equipped with a ventilation system equipped with one (or more often two) activated carbon filters, certified for protection against active ingredients contained in plant protection products. Since the volume inside the cabin cannot be watertight in relation to the external environment, for the effective insulation of the cabin from the polluted environment, it is also necessary that the air pressure in the cabin is (slightly) higher than the atmospheric one, i.e., it is "pressurized". Usually, this effect is achieved with a ventilation system properly upgraded compared to the standard. In this way, when the cabin is closed, it is reasonable to be sure that the air entering the passenger compartment is purified by the filter and can only exit through the cracks in the door and opening windows, therefore providing a good barrier against intrusion from the outside.

 

The activated carbon filters

It is the whole system's key element: the filtering takes place through materials with the carbonaceous structure of vegetable or mineral origin. The filters are inserted in a metal casing that can have different sizes and shapes, but it is usually characterized by two grilled surfaces opposed to each other and transversal to the airflow, between which is located a panel, or a cartridge filled with granular or powdery material. The filters are easily removable in order to make them easy to replace when their filtering capacity fails.

Thanks to the high material porosity and the Van der Waals forces (i.e., attractive forces at the molecular level), the active ingredients of the plant protection products are retained inside the filter while clean air is introduced into the cabin. In some cases, a pre-treatment of the incoming air is provided, optimizing temperature and humidity, in order to improve the pollutant retention.

Usually, the activated carbon filter is produced by specialized manufacturers, who provide for its approval according to the requirements. For this reason, the "category 4" cabin homologation report includes the certificate of the installed filter(s), which states their characteristics and performance.


UNI 15695-1:2018 requirements

A cabin is "category 4" approved if it meets specific minimum requirements to ensure the whole system's effective operation, which may classify it as suitable PPE for plant protection treatments.

In practice, a specific flow rate of air, free of pollutants, blown into the cabin must be ensured, together with adequate pressurization.

It is, therefore required: to ensure that the ventilation system is capable of producing an airflow rate of at least 30 m³/h in order to facilitate proper air exchange; that an overpressure of at least 20 Pa is continuously kept (obviously when the cabin is closed) to avoid infiltration of polluted air from outside. To ensure the ventilation system's proper performance, specific sensors are installed to indicate the amount of overpressure inside the passenger compartment in analog or digital mode.  In fact, it may happen that by adjusting the fans to the minimum, the minimum requirement of the regulations is not ensured.  In this case, the manufacturer must clearly specify, both in the instruction manual and with specific warning stickers, the minimum adjustment parameters necessary to maintain the "category 4" standard; to check the seals' real tightness in the filter housing because the passage of contaminated air from the surrounding environment must be absolutely avoided.  In this regard, the filter's inlet port is completely blocked, making sure that there is no suction.


The Activated carbon role

Activated carbons consist of carbon in the amorphous state and derive from the combustion (in the absence of air and at a temperature below 700°C) of various elements, such as mineral coal, wood, coconuts, synthetic polymers, etc.

They can remove pollutants from an air stream through the adsorption process, i.e., the withholding of a series of principles of organic origin, which can then be further extracted using a carrier made of steam or nitrogen. In practice, the adsorbed substances are trapped inside the coal pores at a molecular level by weak Van der Waals forces, while colloidal particles are placed on the surface of the coal, which in tractor cab filters is in granules or powder form.

The carbon is usually inserted in two filters, the first of which actually adsorbs the pollutants, while the second works in the regeneration phase, dipped in a flow of steam and nitrogen.

However, this cycle cannot last indefinitely because, at a certain point, the coal becomes "exhausted" and must be physically disposed of in a landfill.

by Lavinia Eleonora Galli

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