diff --git a/stand/utils/dfh.py b/stand/utils/dfh.py
index 25dd1be..5cda416 100644
--- a/stand/utils/dfh.py
+++ b/stand/utils/dfh.py
@@ -42,6 +42,31 @@ def dump_non_empty_df(df, fn, key="data"):
         return
     print(f"<<< dump dataframe to {fn}")
     df.to_hdf(fn, key)
+    backup(df, fn, key) #TODO: test then remove
+
+
+
+# the following is just a safety precaution
+# if everything works, it can be removed
+
+from datetime import datetime
+from pathlib import Path
+
+FMT = "%Y-%m-%d_%H-%M-%S-%f"
+BAKDIR = ".backup"
+
+def backup(df, fn, key):
+    Path(BAKDIR).mkdir(parents=True, exist_ok=True)
+    bfn = backup_filename(fn)
+    print(f"<<< backup dataframe to {bfn}")
+    df.to_hdf(bfn, key)
+
+def backup_filename(fn):
+    p = Path(fn)
+    fn = p.stem
+    ext = p.suffix
+    ts = datetime.now().strftime(FMT)
+    return f"{BAKDIR}/{fn}_{ts}{ext}"