diff --git a/DDG4/plugins/Geant4EventReaderGuineaPig.cpp b/DDG4/plugins/Geant4EventReaderGuineaPig.cpp
index 61a783dbe2fd622c588fc72b8a1f6ed4579419ee..92082b406a0ff07a4290244f5b1dfff5c1897d0b 100644
--- a/DDG4/plugins/Geant4EventReaderGuineaPig.cpp
+++ b/DDG4/plugins/Geant4EventReaderGuineaPig.cpp
@@ -80,7 +80,6 @@ namespace dd4hep {
 #include <cerrno>
 
 using namespace std;
-using namespace CLHEP;
 using namespace dd4hep::sim;
 typedef dd4hep::detail::ReferenceBitMask<int> PropertyMask;
 
@@ -233,12 +232,12 @@ Geant4EventReaderGuineaPig::readParticles(int /* event_number */,
     }
 
     //  Momentum vector
-    p->pex = p->psx = betaX*TMath::Abs(Energy)*GeV;
-    p->pey = p->psy = betaY*TMath::Abs(Energy)*GeV;
-    p->pez = p->psz = betaZ*TMath::Abs(Energy)*GeV;
+    p->pex = p->psx = betaX*TMath::Abs(Energy)*CLHEP::GeV;
+    p->pey = p->psy = betaY*TMath::Abs(Energy)*CLHEP::GeV;
+    p->pez = p->psz = betaZ*TMath::Abs(Energy)*CLHEP::GeV;
 
     //  Mass
-    p->mass = 0.0005109989461*GeV;
+    p->mass = 0.0005109989461*CLHEP::GeV;
     //
 
 
@@ -249,9 +248,9 @@ Geant4EventReaderGuineaPig::readParticles(int /* event_number */,
 
 
     //  Vertex
-    p->vsx = posX*nm;
-    p->vsy = posY*nm;
-    p->vsz = posZ*nm;
+    p->vsx = posX*CLHEP::nm;
+    p->vsy = posY*CLHEP::nm;
+    p->vsz = posZ*CLHEP::nm;
 
     Vertex* vtx = new Vertex ;
     vtx->x = p->vsx ;
diff --git a/DDG4/plugins/Geant4EventReaderHepEvt.cpp b/DDG4/plugins/Geant4EventReaderHepEvt.cpp
index dad1a0ce16430f54ed213216fe9fb118c059bb80..0fcb2c085a3195910e1a9277a363281894e130db 100644
--- a/DDG4/plugins/Geant4EventReaderHepEvt.cpp
+++ b/DDG4/plugins/Geant4EventReaderHepEvt.cpp
@@ -89,7 +89,6 @@ namespace dd4hep {
 #include <cerrno>
 
 using namespace std;
-using namespace CLHEP;
 using namespace dd4hep::sim;
 typedef dd4hep::detail::ReferenceBitMask<int> PropertyMask;
 
diff --git a/DDG4/plugins/Geant4EventReaderHepMC.cpp b/DDG4/plugins/Geant4EventReaderHepMC.cpp
index 1b0133eb21b614dc6b4f0d66f57db0e240fb39c4..ad1befbff8cfb21d302e40003025c25abaada7bc 100644
--- a/DDG4/plugins/Geant4EventReaderHepMC.cpp
+++ b/DDG4/plugins/Geant4EventReaderHepMC.cpp
@@ -95,7 +95,6 @@ namespace dd4hep {
 #include <algorithm>
 
 using namespace std;
-using namespace CLHEP;
 using namespace dd4hep::sim;
 typedef dd4hep::detail::ReferenceBitMask<int> PropertyMask;
 
@@ -175,7 +174,7 @@ namespace dd4hep {
         void set_io(int typ, const string& k)
         { io_type = typ;    key = k;                 }
         void use_default_units()
-        { mom_unit = MeV;   pos_unit = mm;           }
+        { mom_unit = MeV;   pos_unit = CLHEP::mm;           }
         bool read();
         void clear();
       };
@@ -279,7 +278,7 @@ Geant4EventReaderHepMC::readParticles(int /* ev_id */,
                "+++ %s ID:%3d status:%08X typ:%9d Mom:(%+.2e,%+.2e,%+.2e)[MeV] "
                "time: %+.2e [ns] #Dau:%3d #Par:%1d",
                "",p->id,p->status,p->pdgID,
-               p->psx/MeV,p->psy/MeV,p->psz/MeV,p->time/ns,
+               p->psx/CLHEP::MeV,p->psy/CLHEP::MeV,p->psz/CLHEP::MeV,p->time/CLHEP::ns,
                p->daughters.size(),
                p->parents.size());
       //output.emplace_back(p);
@@ -619,14 +618,14 @@ int HepMC::read_units(EventStream &info, istringstream & input)   {
     string mom, pos;
     input >> mom >> pos;
     if ( !input.fail() )  {
-      if ( mom == "KEV" ) info.mom_unit = keV;
-      else if ( mom == "MEV" ) info.mom_unit = MeV;
-      else if ( mom == "GEV" ) info.mom_unit = GeV;
-      else if ( mom == "TEV" ) info.mom_unit = TeV;
-
-      if ( pos == "MM" ) info.pos_unit = mm;
-      else if ( pos == "CM" ) info.pos_unit = cm;
-      else if ( pos == "M"  ) info.pos_unit = m;
+      if ( mom == "KEV" ) info.mom_unit = CLHEP::keV;
+      else if ( mom == "MEV" ) info.mom_unit = CLHEP::MeV;
+      else if ( mom == "GEV" ) info.mom_unit = CLHEP::GeV;
+      else if ( mom == "TEV" ) info.mom_unit = CLHEP::TeV;
+
+      if ( pos == "MM" ) info.pos_unit = CLHEP::mm;
+      else if ( pos == "CM" ) info.pos_unit = CLHEP::cm;
+      else if ( pos == "M"  ) info.pos_unit = CLHEP::m;
     }
   }
   return input.fail() ? 0 : 1;
diff --git a/DDG4/plugins/Geant4FieldTrackingSetup.cpp b/DDG4/plugins/Geant4FieldTrackingSetup.cpp
index d6a129e2d04ef1f2e753b641581bfb1a6359765b..3aef6274d51eb04b0d35eab0b00715bffd7b9a2c 100644
--- a/DDG4/plugins/Geant4FieldTrackingSetup.cpp
+++ b/DDG4/plugins/Geant4FieldTrackingSetup.cpp
@@ -148,7 +148,6 @@ namespace dd4hep {
 #include <limits>
 
 using namespace std;
-using namespace CLHEP;
 using namespace dd4hep;
 using namespace dd4hep::sim;
 
diff --git a/examples/DDG4_MySensDet/src/MyTrackerSDAction.cpp b/examples/DDG4_MySensDet/src/MyTrackerSDAction.cpp
index f61171c5c3251cd4724c0929620f2d60a7daeeb0..6ed13a79149b19e8be83c1e8553d5d7d0dfaa3a2 100644
--- a/examples/DDG4_MySensDet/src/MyTrackerSDAction.cpp
+++ b/examples/DDG4_MySensDet/src/MyTrackerSDAction.cpp
@@ -16,7 +16,6 @@
 #include "DDG4/Geant4SensDetAction.inl"
 #include "DDG4/Factories.h"
 
-//using namespace CLHEP;
 
 namespace SomeExperiment {