How to protect yourself from inhaling aerosols

In the article “The Risks of Transmission by Aerosols in the Dental and Medical Practice” we saw what bioaerosols are (a set of invisible airborne particles that can carry viruses, bacteria and spores) and the risks dentists face when doing their job.

In order to prevent and deal with pollution from aerosols inevitably present in the dental practice, the use of barrier products for both the patient and the operators involved become key. When used properly by the patient and worn by operators, this equipment can protect against splashes, spray and fumes visible to the naked eye, and play a crucial role in preventing inhalation, injection or ingestion of pathogens contained in bioaerosols, avoiding contact between mucous membranes with airborne microparticles.

Gloves, eye protection and face shields, and especially the use of respirators and surgical masks are the primary important barrier to manage the risk of infection and limit the transmission and spread of Covid-19.

Depending on the profession and the field of use, patients and operators must wear a certain type of mask with a specific level of protection. Protective masks are divided into surgical masks and filtering facepieces (respirators); they comply with different regulations and perform different functions. These regulations in turn set out different classes, each of which corresponds to a certain level of protection.

Surgical masks are class I medical devices. Their use reduces the risk of direct and/or cross contamination by viruses and bacteria that can cause infections to operators and patients and they protect against chemicals used during medical interventions and must be changed and replaced after each patient.

For dental procedures that do not generate aerosols and/or procedures with isolation of the surgical field using rubber dam, the clinician and the assistant should use uniforms with disposable head covering, surgical masks and visors or glasses.

The current guidelines of the main medical institutions suggest changing your mask every 20 minutes in the presence of high levels of bioaerosols and every 60 minutes during normal procedures.

Filtering facepieces (respirators), such as FFP2 masks come under the category of personal protective equipment (PPE). These are masks that are specially designed to reduce the risk of the wearer inhaling airborne particles and are used mainly in the treatment of infectious diseases. They are used during all treatments that involve exposure to bioareosols of over 15 mins. and/or without protection from other containment systems (e.g. rubber dam), and in the treatment of infected patients who require urgent intervention.

Respirators are tested in the direction of inhalation, i.e. from the outside inwards and the tests they undergo evaluate the effectiveness of the filter and the seal towards the inside of the mask.

Some respirators have an exhalation valve that improves comfort and prevents the formation of condensation or glasses misting up. The use of FFP2 filtering facepieces with valve is permissible only if covered with a surgical mask.

The European reference standard is EN 149:2001, according to which disposable respiratory protective devices to filter particles are divided into three classes:

• FFP1: minimum filtration of 80% and not more than 22% inward leakage. These devices are used primarily as dust masks (DIY and other work).
• FFP2: minimum filtration of 94% and not more than 8% inward leakage. These devices are used mainly in construction, agriculture, the pharmaceutical industry and by medical personnel against influenza viruses, SARS, pneumonic plague, tuberculosis and COVID-19.
• FFP3: minimum filtration of 99% and under 2% inward leakage. FFP3 masks offer the best filtration efficiency and also protect against very fine particles, such as those of asbestos.

In addition, in the United States respiratory protection must meet the requirements set by the NIOSH (National Institute for Occupational Safety and Health). This legislation requires that respirators are categorised according to their degree of resistance to oil, represented, depending on the class, by the letter N, R or P. The number following these letters indicates the percentage of filtration of airborne particles.

Respirators can be divided into:

• Class N: no oil resistance. These are the ones commonly used in the medical field. Within this class, masks are divided into types N95, N99 and N100.
• Class A: oil resistance up to 8 hours. Within this class, masks are divided into types R95, R99 and R100.
• Class P: Total oil resistance. Within this class, masks are divided into types P95, P99 and P100.

In terms of performance, class N95 respirators are equivalent to the FFP2 and the N99 to the FFP3.

The facial respirators used in the medical field are usually the FFP2/FFP3 (N95/N99). These respirators are to be considered disposable and should not be sterilized unless explicitly stated by the manufacturer. Usually facepiece respirators may be used for up to 8 hours or for an entire working day. However, in the medical field it is advisable to be aware that respirators must be replaced as follows:

• after use during procedures which generate bioaerosol;
• if contaminated with blood, respiratory or nasal secretions or other bodily fluids from patients;

Therefore, it is appropriate that the operator uses a visor and covers the respirator with a surgical mask to reduce contamination of the surface. Also, it is necessary to practise hand hygiene with soap and water or an alcohol-based disinfectant before and after putting on the respirator or having touched or adjusted it.

It is unlikely that prolonged use of the respirator, within the limits stated by the manufacturer, impairs functionality. However, it is a good idea to inspect the respirator each time you put it on or take it off in case of any damage. It is also advisable to bear in mind that prolonged use can make breathing difficult. If it becomes too hard to breathe, the respirator must be replaced with another device.

ASTM International (American Society for Testing and Materials International) is an international standards body, a recognised world leader in the development and delivery of international standards in product testing. For masks, the ASTM has established a three-level classification according to 4 performance parameters:

1. Resistance to fluids

The mask helps to reduce the exposure of the wearer to splashes and sprays of blood, body fluids and other potentially infectious materials (OPIM). The fluid resistance is a performance requirement that defines the ability of the mask materials to minimise the passage of fluids through it and therefore the possibility that they are in contact with the wearer. Face masks undergo testing with synthetic blood, with pass/fail criteria and at three speeds corresponding to the range of blood pressure in humans (80,120, 160 mmHg). The greater the pressure withstood, the higher the resistance to fluid splashes and sprays.

2. Bacterial Filtration Efficiency (BFE percentage) @ 3.0 mm

BFE is a value measured as a percentage describing the efficiency with which a face mask filters bacteria, by comparing the inward bacterial concentration with the outward concentration. A higher percentage indicates a higher filtration efficiency (for example, a filtration efficiency of 95% indicates that 95% of the aerosolised bacteria has been retained by the mask, while 5% has passed through the material).

3. Particulate filtration efficiency

This helps to reduce exposure to airborne biological particles, inorganic dust and debris of the wearer. PFE is a value measured as a percentage describing the efficiency with which a face mask filters the particulate matter that passes through the mask, comparing the inward particulate concentration with the outward concentration.

4. Differential pressure

Differential pressure (Delta P) establishes the respiratory fatigue during use of the mask and objectively measures the breathability. The values are expressed in a range from 1 to 5; the higher the number, the higher the PFE and BFE.

The current spread of coronavirus affects working practices in the dental and medical field. In order to restrict the generation of aerosol during dental procedures, isolation of the surgical field is required through the use of a rubber dam capable of significantly reducing the production of aerosols contaminated with saliva and blood in cases where high-speed rotary instruments (Peng et al, 2020).

This generation and the time of exposure to bioaerosols are the variables that need to be evaluated by doctors and assistants in selecting the right personal protection.

Sources

CDC-Interim U.S. Guidance for Risk Assessment and Public Health Management of Healthcare Personnel with potential Exposure in a Healthcare Setting to Patients with Coronavirus Disease (COVID-19)

Xian Peng, XinXu, Yuqing Li, Lei Cheng, Xuedong Zhou and BiaoRen: “Transmission routes of 2019-nCoV and controls in dental practice” – International Journal of Oral Science (2020) 12:9.