diff --git a/src/elements/cbnw.c b/src/elements/cbnw.c
index 478fba73d..80bc19a13 100644
--- a/src/elements/cbnw.c
+++ b/src/elements/cbnw.c
@@ -11,6 +11,12 @@ int update_CBNW(UPDATE_FUNC_ARGS) {
            	parts[i].ctype = 5;
         	pv[y/CELL][x/CELL] += 0.5f;
         }
+        else if(pv[y/CELL][x/CELL]<=-0.5)
+    	{
+            part_change_type(i,x,y,PT_CO2);
+           	parts[i].ctype = 5;
+        	pv[y/CELL][x/CELL] += 0.5f;
+        }
 	}
 	if (parts[i].tmp>0)
 		parts[i].tmp--;