The BW1 Blood-warming bath consists of a polypropylene tank a in plastic-coated steel outer case, with a clamp for attachment to drip stands between 12 and 30mm in diameter. The heater and the bulbs of the control thermostat and the safety cutout are in the base of the tank. They are covered by a perforated stainless steel tray which prevents the heat exchange coil from touching the heater. A dial thermometer indicates water temperature and a flat stainless steel lid is provided.

The pre-set temperature control is set to maintain water temperature at 37°C. At low rates of blood flow, the outlet blood will be at approximately the same temperature as the bath. At higher flow rates, the outlet temperature will depend on the flow rate and the efficiency of the heat-exchange coil.

With blood at an initial temperature of 4°C and using a Portex blood-warming coil, the outlet blood temperature will not fall below 32°C as blood flows up to 100ml/min. The water in the bath warms up from 15°C to 35°C in less than 10 minutes.

Over temperature protection-If the control system fails, an over temperature cut out prevents transfused blood from reaching a temperature where haemolysis could take place. If the safety cut out operates, a warning buzzer sounds and the heater is switched off until the temperature has fallen and a manual reset button is pressed.