TCountOperOrdersThread = class(TThread)
     FQuery : TpFIBQuery;
     TTans : TpFIBTransaction;
     private
        procedure RefrOrdersOper;
     protected
        procedure Execute;override;
  end;

Ontimer 

.......

   CountOrdersOper := TCountOperOrdersThread.Create(true);
   CountOrdersOper.FreeOnTerminate := true;
   CountOrdersOper.Priority := tpLower;
    CountOrdersOper.Resume;

.....

procedure TCountOperOrdersThread.Execute;
begin
  inherited;
  Synchronize(RefrOrdersOper);
end;

 procedure ....Execute
 ......
      FQuery := TpFIBQuery.Create(nil);
      TTans := TpFIBTransaction.Create(nil);

      with TTans do begin
         TRParams.Clear;
         TRParams.Add('read_committed');
         TRParams.Add('rec_version');
         TRParams.Add('nowait');
         TRParams.Add('write');
      end;

      FQuery.Database := DM.FBase;
      TTans.DefaultDatabase := DM.FBase;
      FQuery.Transaction := TTans;

      try
         if not FQuery.Transaction.Active then FQuery.Transaction.StartTransaction;
         with FQuery do begin
             Close;
             SQL.Clear;
             SQL.Add(' запрос.... ну допустим select count(*) from <таблицы>');
            // showmessage(SQL.Text);
             ExecQuery;
         end;

         if FQuery.Transaction.Active then FQuery.Transaction.Commit;
         FQuery.Close;
      except
         if FQuery.Transaction.Active then FQuery.Transaction.Rollback;
      end;

      FreeAndNil(FQuery); FreeAndNil(TTans);

Showmessage(FQuery.FieldByName('cntRec').AsString);