Video Summary - WEBI'MARS Volet 1 l'air à l'hôpital -

Main ideas / lessons from the webinar

Air quality and airborne infection risk in healthcare

Webinar purpose and structure

The organizers ran a short survey after a prior webinar to select new topics.
Because the theme “environment / environmental management” is broad, they split it into three webinars during March.
Today’s webinar topic: risks associated with air quality in healthcare facilities.
The audience can ask questions:
- in writing (question tab), or
- orally (raise hand), with dedicated time at the end of presentations.

Presentation 1 — Mr. Bouillon (Setup)

Standards and engineering of air distribution in operating rooms

1) Regulatory/standards framework mentioned

Operating-room air hygiene is governed by several standards, emphasizing risk-based classification, cleanroom behavior, and air distribution:

ISO 14644 series (cleanroom classification & risk analysis)
- ISO 14644-1: particle classification (examples mentioned: ISO 5, ISO 7, ISO 8).
- ISO 14644-2: risk analysis to assign/increase classification “point” values and determine sampling strategy.
EN 14644-3 (referred to as replaced/updated)
- Noted as shifting toward approaches that account for medical devices, including contamination assessment and sampling.
EN 16890
- Relevant in the context of ventilation air / filtration (subtitle text referenced “heroic distribution,” i.e., ventilation/duct/airflow considerations).
“Air hygiene / air quality Bible”
- EN 13050(351) is described as extremely important and linked to overall air hygiene/quality expectations and costs (subtitle text was noisy but the emphasis was clear).

2) Engineering objective of a cleanroom / operating room

A cleanroom must:

Control contaminants, both
- specific particles and
- microbiological contamination
Control
- entry of people and materials
- hygiene rules
Limit contamination from outside into the controlled zone.

3) How air handling works (outside air → treatment → operating room)

Key mechanisms and risks

A) Outside air intake risk

Air handling units typically draw in outside air, treat it, and distribute it to operating rooms.
Outside air inlets are not always pollution-free.
- Example: a laboratory fume hood near the intake can lead pollutants to “re-enter” the duct/AHU system and then reach rooms.
Lesson: upstream intake sources must be controlled and adequately separated in building design.

B) Air treatment & distribution

Air handling units treat air for hygiene (not just temperature/humidity).
Air may be:
- 100% extracted to outside, or
- partially recycled/remixed with outside air.
Recycling introduces additional issues (including anesthetic gas concentration and contamination control).

C) Single vs centralized AHUs (maintenance complexity)

Dedicated AHU for one operating room is simpler.
Central AHU serving multiple rooms:
- increases maintenance complexity
- shutting down can affect multiple rooms simultaneously.

4) Filtration requirements: why very fine filters are necessary

Key quantitative lesson: 99.9% of particles are smaller than 1 micron.
Therefore, high-performance filtration is required to stop aerosols.
Example context: urban outdoor air can have very high particle counts.
Implication: filtration efficiency must be extremely high between outside air collection and entry into the operating room.

5) Aerodynamic scenarios: where filtration is located + airflow regime

A) Filtration placement concepts

Central AHU filters: duct cleanliness matters to prevent recontamination between AHU outlet and OR supply.
Operating-room terminal filtration: for very stringent classes (e.g., H13/H14 referenced), robust final filtration near delivery is needed.

B) Airflow types: unidirectional vs turbulent (and implications)

Unidirectional flow
- Parallel streams with similar velocity
- Homogeneous coverage of the operating field
- Typically required to achieve ISO 5 reliably
Directional flow “vertical/horizontal”
- Mentioned as analogous to laminar flow hood behavior.
Turbulent flow
- Creates mixing with ambient room air
- Contamination can return into the surgical field due to turbulence/mixing
- Discussed in relation to achieving higher ISO classes (e.g., ISO 7/ISO 8)

6) Air distribution must match the risk class and surgical field

Room designs are chosen based on:

specific class
nature of risk
performance objectives

Examples discussed:

Linear / older ceiling systems
- Deliver clean air to the surgical field
- Turbulence outside the ultra-clean zone
Suspended/covered surgical zone ceiling systems
- Better protection of the ultra-clean zone overall
- Described as “laminar flow” at the highest level

7) Additional operational controls

(energy saving mode, qualification testing, pressure cascades)

A) Standby / reduced ventilation mode

ORs may run reduced ventilation when unoccupied, then restart optimally at surgery start.
Requires testing/verification to confirm performance at activation.

B) Classification parameters (particle counts)

ISO 14644 limits depend on:
- number of particles per cubic meter
- particle diameter
Example referenced:
- ISO 5 thresholds such as 10,000 particles >0.3 µm and 3,500 >0.5 µm.

C) Microbiological aspect (M values)

M1 / M10 microbiological cleanliness categories were discussed.
Relationship to airflow regime:
- under laminar/unidirectional conditions: stricter expectations (near “no microorganisms”)
- under turbulent conditions: less strict (e.g., M10 referenced)

D) Elimination kinetics

Stress on elimination kinetics:
- introduce a pollutant → measure the time to remove 90%
Practical implication:
- helps determine the time between operations for returning to target classification.

E) Pressure cascade (overpressure)

Overpressure helps maintain airflow direction:
- cleanroom → airlock → pushes outward.
Magnitude cited: 15 Pascals ± 5
- too low (e.g., 10 Pa) may fail to offset door openings.
Purpose: prevent exogenous contaminants from entering between protective spaces.

F) Periodic checks

Because contamination can be resuspended if AHU/duct conditions degrade, periodic validation and checks are emphasized.

Q&A points related to Presentation 1 (key themes)

If elimination kinetics weren’t measured during ISO 5 qualification
- Laminar flow may remove contaminants faster, but kinetics are still recommended to identify dead zones under less-than-ideal real conditions.
Return air position (bottom vs top)
- Returns must match the flow design; avoid drawing supply air back from the ceiling.
- Cutting off returns can reduce purge/kinetics.
Filtration class selection across particle sizes
- Compliance may be assessed with one diameter basis, but monitoring multiple diameters can detect drift/leaks.
Microbiology non-compliance despite compliant ISO particle/aerodynamics
- If ISO 5 truly holds for particles/aerodynamics, the likely cause is less about airflow itself and more about other pathways (sampling, cleaning, or very small biological particles).

Presentation 2 — Professor Jean-Christophe Lucet

Clinical risk approach: airborne infection risk across care settings

1) Where airborne ventilation questions arise

Ventilation/airborne infection control targets removal/prevention via:

Immunological barriers (ICU, hematology, transplant)
- Goal: protect patients from incoming air using positive pressure
Physical barriers (operating rooms, burn units)
- Goal: protect the patient site and minimize outgoing contamination using appropriate pressure regimes
High-risk airborne infectious agents
- Emphasized examples: tuberculosis, measles, chickenpox
- Also mentions other airborne viruses, highlighted during COVID-19.

2) Main clinical objectives

Reduce exposure or spread using:
- positive pressure (patient protection from incoming air) in immunocompromised contexts
- negative pressure (prevent escape of infectious agents) in infectious contexts

3) Regulatory landscape (as stated)

No specific broad regulations were described that require hospital-specific air treatment beyond the labor-code baseline ventilation.
Example baseline given: 60 m³/h per person.
Hospitals rely on:
- reference standards/documents, notably AFNOR/EN air hygiene standards (linked to the earlier ISO 14644 risk-based framework).

4) Four “risk levels” and criteria

Risk classes are based on criteria including:

zone delimitation
cleanliness/particle elimination targets
microbiological cleanliness targets
pressure
airflow regime
procedure-specific cleanliness requirements

5) Operating rooms: ISO 5 vs ISO 7 and evidence on SSI

ORs are mostly classified around risk level 3, with exceptions.
The debate summarized:
- ISO 5 is typically associated with laminar flow
- ISO 7 with turbulent flow
Key message from WHO analysis/studies:
- For certain prosthetic orthopedic procedures, evidence suggests no difference in surgical site infection risk between laminar and turbulent ventilation.
- Limitations acknowledged: reliance on observational/registry data.
Important nuance:
- Real OR airflow is disrupted by humans, obstacles, patient warming, and staff movement—so qualification conditions may not reflect true risk.

6) Real-world airborne contamination mechanism (example)

An outbreak pattern was described where aerosols/mist from thermal generators entered the laminar flow environment, deposited, and infections appeared later.

7) Recommendations evolution (prosthetic surgery and laminar flow)

WHO/other guidance evolved over time:
- earlier advice was against laminar flow for certain cases
- later French guidance (SF2H) recommended unidirectional airflow in 2015
- updated in 2018 to allow greater flexibility
However, an AFNOR standard remains a regulatory reference requiring certain ISO levels for specific procedures.

8) Intensive care: pressure and air change rate guidance

Pre-COVID consensus points cited:
- for some risks (e.g., aspergillosis): positive pressure + high air changes
- for airborne infection risks: negative pressure + high air change volumes/hour
COVID-era discussion (2021) for critical care included:
- 8–10 air changes per hour
- absolute filtration
- positive pressure relative to the corridor at a specified value (example given ~10 vs corridor)
- ability to switch toward isobaric conditions when maintaining overpressure is undesirable
- use of airlock-capable rooms

9) Conventional wards: minimal ventilation and CO₂-based confinement control

Risk level 1:
- described as not requiring air renewal in the AFNOR framing.
Practice issue:
- many rooms ventilate little (some use small mechanical ventilation in bathrooms).
CO₂ used as a proxy for crowding:
- examples given for acceptable CO₂ thresholds
- to stay below thresholds, air exchange rates may need to exceed common “two volumes” practice.
Sustainability/energy constraints (e.g., fewer window openings) increase pressure to design ventilation that compensates.

10) Pandemic decision-making: coverage vs whole-hospital upgrades

Key decision: gradual upgrades in parts of the hospital vs full facility upgrades.

Because risk is expected but uncertainty remains, choices must balance:
- complexity and cost
- feasibility and maintainability
- likely effectiveness.

11) Clinical conclusions from this perspective

Operating rooms
- ISO 5 is unlikely to clearly outperform ISO 7 based on current evidence and limited high-level randomized trials.
- ISO 5 is expensive and difficult to maintain.
- Ventilation heterogeneity and uneven application have historically reduced real-world benefits.
Intensive care
- described need: 8 volumes ± 2 of air exchange per unit
- reversing pressure adds complexity; pressure cascades must be validated.

Presentation 3 — Emmanuel Vanoly (Dassault Systèmes)

Simulation-based environmental control

1) Why simulation is used

Airborne transmission was framed as driven by three phenomena:

Emission: contaminated particles emitted by a person
Propagation: spread through ventilated environments
Deposition / resuspension: settling on surfaces or release due to activities

Limitations:

Laboratory testing
- strong measurement control
- but cannot replicate realistic hospital ventilation/architecture
Real hospital testing
- complex: isolating rooms, delaying operations, instrument rooms, etc.

Therefore: 3D simulation (validated tools) is used as a compromise.

2) What simulations model include

Person/patient aerosol emission (including breathing/cough realism)
Hospital architecture
Ventilation system layout and airflow patterns
Heat emission interactions affecting plume behavior

Study A (2020, Bichat Hospital / ICU)

Negative pressure, masks, Optiflow

Goal

quantify particle emission in negative pressure areas (with/without ventilatory support)
estimate healthcare worker exposure risk

Approach

virtual mannequin with detailed upper respiratory anatomy (trachea, glottis, mouth/teeth)
validate airflow assumptions against real tests (Ecole Polytechnique)

Key findings

Ceiling-mounted supply “skims and cools” but can worsen aerosol dispersion control.
Negative pressure + door gaps can create suction patterns that allow plumes to rise and disperse.
Extraction near the ceiling may not effectively contain particles outside its local influence.
After ~1 minute, extraction removes only about half of particles (as described).

Mobile air treatment system (Plasmar, ~1000 m³/h)

Placement matters:
- under extraction can trap particles, reducing extraction performance (e.g., <20% extracted after a minute)
- opposite the door to guide airflow toward extraction improves capture vs a bed-only baseline.

Study B (early 2021, Saint-Joseph Hospital ICU)

Vent layout optimization

Problem

episodes of airborne contamination; rooms looked similar but outcomes differed.

Method

simulation of airflow and particle accumulation based on subtle vent-position/geometric differences.

Findings

Small variations in vent spacing relative to patient position and between vents can strongly affect:
- where particles accumulate
- how quickly rooms decontaminate
Experimental aerosol tests confirmed simulation dynamics.

Intervention

redesign airflow patterns without changing the ventilation rate setting
aim: direct particles back toward exhaust vents and reduce dead zones
targeted room layouts (including triangular concept + exhaust close to patient)
simulations showed improved decontamination when extraction captures the plume before it disperses.

Study C (PACU at Pitié-Salpêtrière, Oct 2020 → Jan 2021)

Unexpected particle propagation in COVID zones

Scenario

PACU planned COVID zones and patient separation, but unexpected particle spread occurred.

Simulation revealed

cross-shaped ceiling airflow spreading to distant zones within tens of seconds
near-direct transmission to two patients positioned along the problematic airflow routes.

Actions

rapid simulation-led modifications within days
aerosol counting tests and further university verification

Engineering changes

break the cross-shaped airflow pattern:
- replace ceiling fins with a perforated “box/sheet” to reduce velocities and disperse between zones
partition between patients
add extraction vents behind patients connected to ducting
- tested slight negative vs slight positive pressure
- negative pressure performed better, while positive pressure worsened efficiency and increased escape risk.

Outcome

modifications became permanent and extended to other units (including maternity-related contexts) based on team acceptance.

Study D

Surface contamination prediction + weather-driven deposition