Firefighters Kris Robb (left) and Karen Brown use a gas
detector to check CO2 and oxygen levels at the Clyde dam.
Clyde and Alexandra fire crews were faced with a
relatively unknown situation at 9am yesterday, after a large
bank of CO2 cylinders activated at the Clyde dam.
The cylinders, which are part of an automated system designed
to smother any electrical fire in the huge generators at the
dam were inadvertently triggered by maintenance workers
setting off fire alarms, Contact Energy's Clyde dam manager
Graham Quinn said.
One appliance from Clyde and two from Alexandra were
dispatched to the scene.
"CO2 is designed to displace oxygen and breathing apparatus
(BA) gear is a must for anyone going near the affected the
area. We sent crews down in BA gear with gas detectors and
they confirmed the system had been activated," Clyde Chief
Fire Officer Richard Davidson said.
The generator was not running at the time and had not caught
"If a generator goes on fire you can't pour water into it, as
it is generating huge amounts of electricity, so you flood it
with CO2, and there were large banks of CO2 cylinders there
including a second set of spares," Mr Davidson said.
Extractor fans designed to remove the CO2 immediately
activated, but because the system had never been used or
tested no-one knew how long it would take to clear the CO2
from the area, he said.
CO2 is heavy and the residue would be collecting in the
drains way below the dam.
Firefighters wearing BA gear had to go down into the bowels
of the dam yesterday afternoon to make sure all the CO2 had
If there was any gas remaining, they would keep checking
every few hours until it was all clear, he said.
Electricity generation was not affected by the incident.
Contact Energy has been spilling water from the dam over the
past few weeks to help reduce a glut in the supply of
electricity after one of the main potlines at the Tiwai Point
aluminium smelter was shut down due to damage to a
Contact energy communications manager Jonathan Hill said
Contact was not able to send the excess electricity out of
the area as transmission lines were constrained.
Mr Hill said it highlighted the critical importance of
investment in the transmission system.
Tiwai uses about 15% of the country's electricity and Contact
had been forced to spill up to 7GWh (gigawatt hours) worth of
water from Lake Roxburgh and Lake Dunstan over the past few
That figure has dropped to 2GWh over the past couple of days.