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 Standards of Medical Masks for Infection Prevention in Vietnam

Standards of Medical Masks for Infection Prevention in Vietnam


Medical face mask – Part 2: Medical face mask preventing bacteria

1. Scope of application

This standard applies to surgical masks to prevent infection.

Medical masks to prevent infection have the effect of preventing and killing 99.9% bacteria right on the surface of the mask.

2. References

The following referenced documents are essential for the application of this standard. For dated references, the cited version applies. For undated referenced documents, the latest version, including amendments and supplements (if any), applies.

TCVN 4851:1989 (ISO 3696:1987) Water used for laboratory analysis

TCVN 8389-1:2010 Medical masks – Part 1: Ordinary medical masks

3. Technical requirements

3.1. General rules: according to TCVN 8389-1, Article 3.1.

3.2. Structure

3.2.1. Medical masks to prevent infection include the following parts:

– the fabric layers may have 2 to 4 flat corrugated layers or 5 to 7 muzzle layers;

– microfiltration layer;

– fabric impregnated with nano-silver;

– nose splints;

– nose pads, straps;

– strap adjustment buckle (if necessary);

3.2.2. Style, size

Design and size according to TCVN 8389-1, Article 3.2.2.

3.3. Requirements for materials

3.3.1. Fabric layer: use fabric with smooth surface, breathable, waterproof and dustproof.

3.3.2. Air-permeable microfiltration layer is waterproof.

3.3.3. The fabric is impregnated with nano-silver, which has a bactericidal effect.

3.3.4. Flexible metal bars: use aluminum foil to ensure malleability, keep the shape after bending, or you can use other types with similar features.

3.3.5. Nose pad: soft, does not cause skin irritation.

3.3.6. Strap: use elastic wire, making it easy to put on and take off the mask.

3.3.7. Strap adjustment buckle (if needed).

3.4. Technical specifications of masks

Technical specifications of masks according to TCVN 8389-1, Article 3.4.

3.5. The ability to protect against infection

The ability to protect against infection of medical masks to prevent infection is determined based on the level that allows the number of bacteria to enter through the medical mask according to Table 1.

Table 1 – Permissible levels of bacteria entering through medical masks

Air flow through the mask, L/minAir flow time through the mask, minPermitted levels
1030Must not have

NOTE The airflow through the mask is 10 L/min (equivalent to the normal human respiratory flow rate).

3.6. Sterility

Masks after being sterilized must meet the following requirements:

– anaerobic bacteria: not present;

– aerobic bacteria: not present;

– colonies: not present;

3.7. Permissible limits of heavy metal elements in nonwovens

Permissible limits of heavy metal elements in nonwovens according to TCVN 8389-1. Article 3.5.

4. Test method

4.1. Structural inspection, material requirements

Check structure, requirements for materials according to TCVN 8389-1, Article 4.1.

4.2. Determination of protection against infection

4.2.1. Rule

Aspirate a normal air stream (contaminated with airborne microorganisms) passing through the mask with a flow rate of 10 L/min into a pre-diluted container with diluted water for the specified time and culture on the medium. selective.

Read the number of colonies grown on the culture medium.

4.2.2. Warning

– all glassware must be sterilized.

– the test area must be sterilized with a UV lamp before proceeding.

– handle gently to avoid breakage of tools and spread of infection.

– gases containing formaldehyde vapor to clean the test system shall be absorbed in the solution.

– the test should be carried out in a biosafety cabinet.

4.2.3. Appliances

- Autoclaves;

- sterilization cabinet by hot air;

– oven, temperature regulation and control to 130 °C;

- incubator, temperature regulation and control to 50 °C;

– tincubate biological safety;

- electronic scales, accuracy to 0.01 g;

– water bath;

- microscope;

– pH meter;

– test equipment system with air flow equal to (0.5 ¸ 0.6) m3/H.

– triangular vase, 250 ml capacity;

– pipette 1 ml;

– implant; scissors, tongs, glass rod, alcohol lamp, measuring tube, petri dish, test tube types;

– test box.

4.2.4. Chemistry substance, environment

Chemicals used in the test must be pure chemicals. The water used during the test shall be distilled water according to ISO 3696. Peptone water with jelly

Peptone 10 g

NaCI 5 g

Agar 12g

Meat 3 g

Distilled water 1000 ml

Dissolve the above ingredients in the water. Place 100 ml in a 250 ml conical flask. Autoclave at 121 °C for 15 min. Mixed salt waterãng

NaCI 8.5 g

Distilled water 1000 ml

Dissolve NaCI in water. Place 100 ml in a 250 ml conical flask. Autoclave at 121 °C for 15 min. Microbial samples

Microorganisms are cultured, grown to the extent that they can be dispersed in the air, or directly from a natural air source where microorganisms grow.

4.2.5. Prepare to try

– installation of test equipment systems;

– put the mask in the test box;

– clean the test device system with formaldehyde gas 30% ¸ 40% for 30 min by placing the tip of the straw in a container containing formaldehyde solution 30% ¸ 40%. The end of the waste pipe is safely exposed to the outside environment (absorbed in water). Allow the system to operate for 30 min.

Proceed in the same manner as above with a clean air source for a period of 30 min;

– place the microbiological sample in the test box.

4.2.6. How to proceed?

– place the normal air duct to the outside environment.

– adjust the airflow through the mask to stabilize at the value X = (10 ± 0.1) L/min.

– allow the system to operate for a defined period of time T = (30 ± 0,1) min.

– carefully stopper the flask, shake well and allow to stabilize for 2 min.

– accurately aspirate 1 ml of diluted saline solution into a petri dish. Add about 15 ml of medium (cooled to 40°C + 50°C). Mix well by swirling the dish in a circular motion, clockwise and anti-clockwise, 5 times each.

– after the agar has frozen, turn the dish upside down and place in a 37 °C incubator for (24 ¸ 72) h.

– The blank sample is conducted similarly but without the mask.

4.2.7. Read the results

Count the number of colonies growing on the two plates. Calculate the number of aerobic microorganisms present in a unit volume of air as follows:


C is the total number of colonies growing on both plates;

X is the air flow through the mask, in liters per minute (L/min);

T is the time to draw air through the mask, in minutes (min).

4.3. Check for sterility

Check the sterility according to the Vietnam Pharmacopoeia volume II volume 3 (published 1994), Appendix 8.1.

4.4. Determination of allowable limits for heavy metal elements in nonwovens

Determination of allowable limits of heavy metal elements in nonwovens according to TCVN 8389-1, Article 3.5.

5. Packaging and labeling

Packaging and labeling according to TCVN 8389-1, Article 5.