Volume 13 - The Science of Airborne Risk, PPE Failure and Why Exposure Persists

Why can contaminated environments remain dangerous even after PPE, air filtration and remediation controls have been put in place?

In The Science of Airborne Risk, PPE Failure and Why Exposure Persists, Jeff Charlton examines the physical and biological mechanisms that allow contamination to remain airborne, move through buildings and continue exposing occupants long after intervention has begun.

This thirteenth volume of the Building Forensics Legacy Series challenges the assumption that exposure is a single event. Instead, it presents exposure as an ongoing process shaped by dose, time and the behaviour of air within a building.

The book explains that air is not empty space. It is a transport system influenced by temperature, pressure, convection, turbulence and particle interaction. Once contamination becomes airborne, it can travel beyond the original source and create a wider exposure environment.

Inside this volume

• Why exposure is a process rather than a single event
• The relationship between dose, time and air behaviour
• How particles move through indoor environments
• Why particle size determines depth of inhalation
• Air stratification and the vertical breathing-zone risk
• Brownian motion and persistent fine particles
• Why dead mould can remain biologically active
• Fragmentation as an exposure multiplier
• The true capture limits of Negative Pressure Units
• Competing airflows and short-circuiting
• Why PPE performance can collapse during real use
• Face-seal leakage and bypass exposure
• Behavioural compensation caused by false confidence
• Why laboratory success may not translate into buildings
• Moisture dynamics and persistent contamination
• Why visual clearance cannot prove safety
• Why occupants may feel worse after remediation
• The role of verification, source control and material removal

A major focus is particle size. Larger particles may settle relatively quickly, while smaller fragments can remain airborne, travel deeper into the lungs and bypass the upper airway’s natural defences. The most biologically active fraction may also be invisible and non-viable, meaning it can be missed by visual inspections and conventional culture-based testing.

The book also explains the importance of air stratification. Indoor particles do not form one uniform cloud; they can remain at different heights depending on temperature, buoyancy and airflow. This creates different exposure zones, particularly in bedrooms where people remain in one breathing position for several hours.

Negative Pressure Units are examined in detail. The volume argues that a single unit does not clean an entire room and only provides meaningful capture within a limited area around the inlet. Beyond that zone, particles remain governed by competing pressure pathways, movement and stratification.

The volume also challenges idealised claims about PPE. Laboratory testing assumes correct fit, stable conditions and perfect use, while real-world environments involve movement, moisture, fatigue, touching, talking and damaged seals. Under those conditions, theoretical protection can fall rapidly.

The central conclusion is that the objective is not simply to kill contamination or complete a procedure. The objective is measurable exposure reduction through source control, removal of contaminated materials, effective air management and scientifically defensible verification.

Written for

Housing providers, remediation contractors, environmental health professionals, insurers, safety specialists, clinicians, regulators, legal teams and anyone responsible for managing airborne contamination or building-related illness.