Bioaerosols Travel Vertically Through Building Drainage Stacks, Reaching Multiple Floors Above and Below the Source.
Key takeaway.
CFD modeling shows that bioaerosols generated in drainage systems travel vertically through building stacks, with pressure differentials up to 3,200 Pa driving transmission across multiple floors. Lower building positions amplify the spread, and trap seal performance is critical for preventing vertical transmission.
The study.
When most people think about infection transmission in buildings, they think about horizontal spread: person to person within a room or floor. Liu and Xi investigated a less obvious but equally important pathway. Their CFD modeling demonstrates that bioaerosols generated in drainage systems travel vertically through building drainage stacks, affecting residents on multiple floors above and below the source.
The researchers modeled various scenarios across different flush volumes (1.28L to 6.5L), pipe configurations (2", 3", 4"), and building heights (2 to 6 stories). They found that pressure differences at drainage points range from 900 to 3,200 Pa depending on flush volume and floor level. These pressure differentials are substantial, and they create conditions that can overcome inadequate trap seals. Drainage points positioned lower in buildings experience greater pressure differential effects and enhanced vertical transmission.
The modeling demonstrates that standard P-trap configurations, while providing some seal, do not always prevent aerosol transmission across multiple building levels. The vertical transmission mechanism is driven by pressure differentials created during water discharge, which can overcome or bypass conventional water seal protection in lower-performing trap designs. This has direct implications for residential buildings where drainage stacks connect units on every floor.
Key findings.
- Vertical transmission pathway confirmed Bioaerosols generated in drainage systems travel vertically through building drainage stacks, affecting units on multiple floors, not just adjacent units.
- Pressure differentials up to 3,200 Pa Recorded pressure differences at drainage points range from 900 to 3,200 Pa depending on flush volume and floor location, creating conditions that can overcome inadequate trap seals.
- Lower positions amplify spread Drainage points positioned lower in buildings experience greater pressure differential effects and enhanced vertical transmission of bioaerosols upward through the stack.
- Trap seal performance is critical The modeling demonstrates that trap seal performance is essential for preventing vertical bioaerosol transmission, with poor seals allowing significant upward penetration of contaminated air.
- Multi-floor infection risk documented Bioaerosols originating from drainage systems in one residential unit can reach and potentially infect residents in units on different floors of the same building.
What this means for your facility.
This research makes clear that drainage systems in multi-story buildings are not isolated floor by floor. They are connected vertical pathways where bioaerosols can travel from one unit to another through shared drainage stacks. The pressure differentials documented, up to 3,200 Pa, are generated by normal building drainage operations like toilet flushing. This is not an unusual condition. It happens every day in every multi-story building.
Green Drain's silicone one-way valve provides mechanical resistance that significantly exceeds the pressure differentials identified in this research. This ensures that vertical bioaerosol transmission through the trap is prevented even under high-pressure discharge scenarios. Unlike water trap seals, which can be overcome by sufficient pressure or depleted by evaporation, Green Drain's mechanical seal maintains integrity regardless of the pressure dynamics occurring in the drainage stack.
While much drain safety research focuses on hospitals, this study highlights the relevance of drainage system design in residential buildings. Multi-family housing, apartments, condominiums, and student housing all share the vertical drainage stack configuration studied here. Green Drain's availability across sizes from 1.25" to 6" means it can protect fixture drains and floor drains throughout residential buildings, providing critical protection against vertical bioaerosol transmission between units.
Green Drain's compliance with ASSE 1072-2020, which specifies trap seal performance requirements, ensures protection against the transmission pathways identified in this modeling study. The SGS pathogen test (Report QDF25-0049810-01) demonstrated that the GD3 blocks over 99.9% of viral aerosols from passing through the drain, directly addressing the vertical bioaerosol transmission pathway this research documents.
Full citation.
Related research.
Protect your facility's drains.
Green Drain's waterless trap seal provides a mechanical barrier backed by independent testing. See how it works for your industry.