B737 Maintenance Technician reported freeze spray is hazardous without proper ventilation and found that the Boeing AMM does not warn about oxygen displacement.

Narrative

All Maintenance; Line and Heavy; Leads; Inspectors; Engineering; SMS.What this is about: Freeze spray is used to test heaters on gray water drain lines in various aircraft locations; including confined and low-airflow areas. Found out last night the threat of suffocation is real.The hazard: Per the manufacturer's Safety Data Sheet; this spray is a liquefied gas that: displaces oxygen; vapors are heavier than air; [and] can cause rapid suffocation with no warning. Boeing Aircraft Maintenance Manual (AMM) allows the spray but does not warn about oxygen displacement.Where this gets risky: Cargo compartments; bilge/underfloor areas; and any closed or poorly ventilated space.Bottom line: You can pass out before you know there's a problem.Suggested resolution: Bulletin: Do not use freeze spray without ventilation. Open doors or establish airflow first. Use minimum amount. If airflow can't be ensured; use another method. Dizziness or shortness of breath = stop and get out. Remember: AMM approval does not remove SDS hazards. Safety first.