Monitoring, Aeration, and Clearance Procedures
Why monitoring matters
Concentration readings confirm the dose actually delivered, reveal leaks, and document the exposure that the label requires. Take readings at representative locations - high, low, and far from release points - because heavy gases stratify. Two readings separated by a known interval let you calculate the half-loss time: a short half-loss means excessive leakage, and the correct response is to reseal and recharge rather than to keep waiting.
Understand instrument limits. Thermal-conductivity analyzers measure total gas and are confused by carbon dioxide, moisture, and solvent vapors; colorimetric tubes are compound-specific but cross-react; electronic sensors drift and need calibration. Record the device used, calibration date, reading, location, and time.
Aeration
Aeration is a controlled operation, not simply opening the tarp. Follow the label sequence: remove or open the tarp in the specified order, use fans and open vents to sweep gas out, keep barriers and placards in place, and keep unprotected people away while concentrations fall. Re-entry during aeration requires the same PPE as the fumigation itself.
Clearance
Clearance requires a measured concentration at or below the label's clearance level, taken with an approved, calibrated device by a qualified person, in every occupied space including crawlspaces and attached units. Only then are placards removed and the structure released to occupants. Document the final reading and the time.
Traps
Releasing a structure because "enough time has passed"; using one reading from one room; clearing on a thermal-conductivity meter in a space with high CO₂; and forgetting that contents, especially porous goods, can re-release sorbed fumigant after clearance.