function showdiv (targetdiv) {
  document.getElementById('smokedetectors').style.visibility='hidden';
  document.getElementById('heatingsystem').style.visibility='hidden';
  document.getElementById('candlesafety').style.visibility='hidden';
  document.getElementById('codetectors').style.visibility='hidden';
  document.getElementById('sprinklersystem').style.visibility='hidden';
  document.getElementById('fireextinguishers').style.visibility='hidden';
  document.getElementById('flammablepaint').style.visibility='hidden';
  document.getElementById('escaperoute').style.visibility='hidden';
  if (targetdiv) {
    document.getElementById(targetdiv).style.visibility='visible';
  }
}