Exhibit 21 THERMO REMEDIATION INC. Subsidiaries of the Registrant As of May 23, 1997, Thermo Remediation Inc. owned the following companies: STATE OR JURISDICTION PERCENT NAME OF OF INCORPORATION OWNERSHIP Eberline Holdings Inc. Delaware 100 Eberline Analytical Corporation New Mexico 100 Thermo Hanford Inc. Delaware 100 TMA/NORCAL Inc. California 100 IEM Sealand Corporation Virginia 100 Remediation Technologies, Inc. Delaware 100 RETEC Thermal, Inc. Delaware 100 ReTec/Tetra L.C. Texas 50* TriTechnics Corporation Colorado 100 Thermo Fluids Inc. Delaware 100 TPS Technologies Inc. Florida 100 TPST Soil Recyclers of California Inc. California 100 California Hydrocarbon, Inc. Nevada 100 TPST Soil Recyclers of Maryland Inc. Maryland 100 Todds Lane Limited Partnership Maryland 100* (1% of which is owned directly by TPS Technologies Inc.) TPST Soil Recyclers of New York Inc. New York 100 TPST Soil Recyclers of Oregon Inc. Oregon 100 TPST Soil Recyclers of South Carolina Delaware 100 Inc. TPST Soil Recyclers of Virginia Inc. Delaware 100 TPST Soil Recyclers of Washington Inc. Washington 100 TMA/Hanford, Inc. Washington 100 Thermo Securities Corporation Delaware 100 Thermo Soil Recyclers Inc. Massachusetts 100 Thermo Technology Ventures Inc. Idaho 100 Plasma Quench Investment Limited Partnership Delaware 60* * Joint Venture/Partnership