17 April 2012

In 2007 three fatal accidents occurred when homeowners stapled under floor thermal (aluminium foil-style) insulation material into power cables.

When stapling under floor thermal insulation it is essential to keep staples well clear of any power cables.  Damage to such a power cable may result in a fatal electric shock.

Power isolation when performing the work is encouraged.  However, it should be noted that turning off the power will not necessarily eliminate the electric shock hazard as a damaged cable may liven the aluminium foil when power is turned back on.

There is also risk of an electrically initiated fire resulting from such a damaged cable.  

• If you have any doubts or concerns about installing this thermal insulation safely then please have the work carried out by professional installers.

Another incident further emphasised the importance of performing pre-installation hazard assessment and subsequent isolation of potential electrical hazards.

Power cables must be identified and barriers provided as required to prevent staples piercing them when installing under floor thermal insulation.

In this incident, power was switched off and then the aluminium foil insulation was installed.  Power was restored after the installation work was completed.  A voltage check was then made between the foil and earth, no voltage was detected.

Subsequently the owner of the premises discovered that a hot-point circuit in the house had no electricity supplied to it.  This was investigated by the homeowner who found that the fuse had blown.  He replaced the fuse and it immediately blew again.  On investigation a TPS power cable was found to have been stapled.

While switching off the power supply prevented a fatal accident, the electrical installation was left with a damaged power cable in contact with the aluminium foil – an accident waiting to happen.

The accidentally stapled cable created a direct path for the electricity through the staple onto the foil.  When the power was switched on, the fuse blew.  Tests were carried out for voltages on the aluminium foil.  No voltages were detected due to the fact that the blown fuse had isolated the power from the circuit concerned.

The above highlights the need for checking the state of the circuit protection devices on the switchboard when the power is restored.  If any changes are observed such as a circuit breaker tripping or a fuse blowing then an electrician should be engaged to investigate and carry out any repairs if required.

There is still a possibility of damage to the cable by a staple and the protective devices not operating (fault current being not enough to activate the protection). This will result in the aluminium foil becoming live when the power is restored.  For this reason it is vital that checks be carried out on the aluminium foil for voltages in all cases.

Prevention is the key

Performing the pre-installation hazard assessment is critical, as is

• The subsequent isolation of electrical hazards prior to the installation work starting, and
• Safety checks being performed at the conclusion of the installation.
• Plastic staples should be used whenever possible as this would alleviate the risk of electric shock to the installer.

As an outcome the above actions should play a part in preventing future accidents when installing under floor insulation.

Any questions or for further advice, please don’t hesitate to contact WorkSafe.