What are the advantages and disadvantages of face shields?
Advantages of Face Shields
- More comfortable
- Protect a larger portion of the face
- Less retained dermal facial heat
- Less fogging than goggles (the Akhani shield is designed with venting slots on the headband to reduce misting)
- Less claustrophobic
- No impact on breathing resistance
- No fit testing required
- Can be disinfected easily
- Wearers do not need to be clean-shaven
- Easy to put on and take off
- Relatively inexpensive
- No impact on vocalization
- Can be worn concurrent to other face/eye PPE
- Do not impede facial nonverbal communication
- Reduced patient anxiety
- Protects against self-inoculation over a wider facial area
- May extend the useful life of a protective facemask when used concurrently
Disadvantages of Face Shields
- Glare (The Akhani shield uses PETG – most face shields use the cheaper PET plastic. The visual difference between PETG and PET is significant)
- Fogging (the Akhani shield is designed with venting slots on the headband to reduce misting)
- Optically imperfect (The Akhani shield uses PETG – most face shields use the cheaper PET plastic. The visual difference between PETG and PET is significant)
- Some models may not fit properly over some respirators (e.g., duckbill filtering facepiece respirators)
- Bulkier than goggles and safety glasses
- Peripheral fit poorer than protective facemasks
Can plastic face shields prevent the spread of coronavirus?
Face shields provide a barrier to acutely-expelled aerosols of body fluids and are commonly used as an alternative to goggles as they confer protection to a larger area of the face.
However, as highlighted in a recent Institute of Medicine report, little is known about the effectiveness of face shields in preventing the transmission of viral respiratory diseases.
Utilizing a cough aerosol simulator loaded with influenza virus (aerosol volume mean diameter of 8.5 µm) and a breathing simulator, Lindsley et al. reported 96% and 92% reductions in the risk of inhalational exposure immediately after a cough for a face shield at distances of 18 in (46 cm) and 72 in (183 cm), respectively.
Decreasing the aerosol size to 3.4 µm resulted in the face shield blocking 68% of the inhalational exposure at 18 in (46 cm) immediately after the cough and 23% over 1–30 min post-cough (during which time the larger aerosol particles had settled out and droplet nuclei had formed and remained airborne so that flow occurred more easily around the edges of the face shield).
Shoham et al. sprayed a fluorescent dye (particle diameter ∼5µm) at a distance of 20 in (50 cm) away from a mannequin head outfitted with various types of PPE.
They found that a face shield with head/neck length, three separate contact points at the forehead, and side curve reaching to the point of the ear, or the combination of this kind of face shield and an N95 filtering facepiece respirator (N95 FFR), protected the eyes, nares, and mouth from contamination.
Conversely, these same investigators found that the use of safety glasses with either a surgical mask or N95 FFR resulted in some eye contamination.
Mansour III et al. utilized a mannequin head to study eye (conjunctival) contamination during a performance of a femoral osteotomy and found a 30% incidence of contamination when using a combination surgical mask with integral eye shield (visor) and 3% for disposable plastic glasses.
Utilizing an aerosolized dye (mean particle size 4.8 µm) emitted at a distance of 6 in (15 cm) from subjects wearing two models of face shields, Christensen et al. noted that the face shields were inferior to two models of surgical face masks tested similarly for particle penetration and that the combination of one of the facemasks with a face shield improved results only marginally. These face shield results were attributable to the lack of a peripheral fit.
In a human study using sprayed water during simulated surgery, Loveridge et al. observed a 40.5% incidence of contamination of the inner surface of a combination surgical mask with integral visor and 6.5% contamination of the wearers' face.
Bentley et al. demonstrated that use of a face shield by dental personnel during simulated dental procedures on a mannequin head did not prevent aerosol contamination of a concurrently worn, cup-shaped surgical face mask.
Monkey-related Cercopithecine herpesvirus 1 (B virus) infection has been reported in an animal handler and SARS in a nurse, both of whom were wearing a combination surgical mask with integral visor.
An epidemiological study reported that the nonuse of face shields by nurses, during high-risk aerosolizing procedures on patients with respiratory infections, resulted in a greater than three-fold increased risk of infection.
The use of face shields alone for three months, compared with the use of face masks alone for an equal period, during thoracic and general surgeries resulted in no difference in infection rates of patients.
Clearly, there is a need for further research into the protection from infectious airborne pathogens afforded by face shields either worn alone or in conjunction with other PPE worn simultaneously. This should include well-designed aerosol transmission studies, as well as possibly pursuing innovative approaches to design and function (incorporating miniature fans to purge air from the face shield dead space, application of biostatic films for decontamination purposes, etc.).
How do I select a face shield?
Face shields are meant to be used as barrier protection for the facial area and associated mucous membranes from airborne body fluids (blood, saliva, bronchial secretions, vomit, urine, etc.) expelled as a result of various physiological processes (vomiting, coughing, sneezing, etc.) and medical, dental, and veterinary procedures (suctioning the airway, placing nasogastric tubes, obstetrical procedures, surgery, dental procedures, etc.).
Inasmuch as there are currently no standards for face or eye protection against biological hazards, and research data is scant, recommendations for the proper selection of face shields for infection control must rely on currently available knowledge, the task to be performed and the anticipated risk associated with the procedure.
The selection of the most appropriate face shield model(s) will depend on the circumstances of exposure, other PPE used concurrently, and personal vision needs.
Face shields with single Velcro or elastic straps tend to be easiest to don and doff; doffing can be accomplished with a single hand.
Visors that offer protection from UV light would be an important feature for individuals utilizing UV light sources (e.g., dental personnel). Face shields should be selected that have visors treated for anti-glare, anti-static, and anti-fogging properties.
For improved protection from infectious agents, face shields should be, at a minimum, full face length with outer edges of the face shield reaching at least to the point of the ear, include chin and forehead protectors, and cover the forehead.[7, 12, 13]
Brow caps or forehead cushions should be of sufficient dimensions to ensure that there is adequate space between the wearer's face and the inner surface of the visor to allow for the use of ancillary equipment (medical/surgical mask, respirator, eyewear, etc.).
Cost-effective considerations include disposable face shields vs. reusable models and those that offer replaceable parts.
Although some models of industrial face shields could be used for infection control purposes (e.g., in the event of face shield shortages), they generally tend to be more expensive, heavier, and bulkier than face shields used for infection control purposes. This is not the case with the Akhani Face Shield, as the design uses a lightweight design.
What is the proper use of a face shield?
Correct use of a face shield is dependent upon the indications for use.
Appropriately fitted, indirectly vented goggles such as the Akhani Industrial Face Shield offer the most reliable practical eye protection from splashes, but face shields are considered an alternative to goggles for prevention of eye contamination with infectious agents.
Any additional protection afforded the eyes when protective eyewear (e.g., safety glasses or goggles) is combined with a face shield has not been thoroughly investigated, though the combination of a face shield and goggles has been espoused for use during invasive surgical procedures.
The combined use of some forms of protective eyewear with a face shield may impact visual clarity and limit peripheral vision to some extent and these effects must be taken into consideration before use.
Use of a face shield alone for eye, face, and mucous membrane protection from contamination by body fluids is likely insufficient and it has been recommended that in those situations where a face shield is used to protect against splash or splatter, a medical/surgical mask would also be indicated.
Face shields are not meant to function as primary respiratory protection and should not be used alone because aerosols can flow behind the visor,[16, 19, 21, 41] so a protective facemask (medical/surgical mask, N95 FFR, etc.) should be worn concurrently.
In those instances where aerosolization of body fluids of infectious individuals is likely to occur (suctioning the airway, intubation, etc.), a respirator (e.g., N95 FFR, at a minimum) should be used in conjunction with the face shield.
Medical | surgical masks with integral visors should not be relied upon as optimal protection, as evidenced by facial and ocular contamination in human and nonhuman research studies[17, 18, 20] and human ocular exposure to infectious agents when wearing these combination devices.[22, 23]
The recommended PPE donning and doffing sequence for a face shield in healthcare settings should be followed (donning sequence is the gown, protective facemask, face shield [or goggles] and gloves; the doffing sequence is the reverse) keeping in mind that it may vary according to the equipment needed for the particular hazard.
Although some models of industrial face shields could be used for infection control purposes (e.g., in the event of face shield shortages), they generally tend to be more expensive, heavier, and bulkier than face shields used for infection control purposes. This is not the case with the Akhani Industrial Face Shield as it ha been designed to be lightweight and cost-effective.