Chris de Freitas warns of the health dangers of leaving your child locked in a vehicle
A few minutes can mean the difference between life and death to an infant or young child locked in a parked car.
A US study found that heat-related deaths to young children trapped in parked cars averaged 36 per year from 1998 to 2007. No figure was given for heat-related
injury, but it is feasibly greater.
Equivalent statistics for New Zealand could not be found, but it is clear the risk is high.
An incredible 918 children were locked in cars in incidents reported to the NZ Automobile Association for the 12-month period from December 2008 to November 2009.
Under clear-sky conditions in summer, temperatures inside cars have been observed to increase by up to 27C within an hour and reach temperatures as high as 89C, well in excess of the temperature level that medical experts warn can be fatal.
The temperature increase in a closed car is caused by the build up of trapped heat from the sun in the passenger cabin area. The level reached depends mainly on climatic conditions.
A study reported last year in the International Journal of Biometeorology is the first to examine car-cabin temperatures under variable weather conditions.
In tests conducted during spring and summer in Athens, Georgia, University of Georgia biolclimatologists Andrew Grundstein, Vernon Meentemeyer and John Dowd found maximum vehicle cabin temperatures ranging from 41C to 76C, depending on the weather and intensity of the sun.
Clear days had the highest cabin temperatures, with average values of 68C in the summer and 61C in the spring. Cabin temperatures on cloudy days in the spring and summer were on average approximately 10C cooler, but still reached deadly levels.
Tests by the Royal Automobile Club of Queensland showed that a car's cabin temperature can rocket from an air-conditioned 19C to 30C in one minute and reach 40C in just seven minutes.
During one test the temperature inside the car peaked at 75C, with the surface temperature of the steering wheel reaching 83C. The air temperature outside on the test day was 32C.
In these situations children are unable to withstand the heat build-up. Medical experts warn that if internal body-core temperatures over 40C are sustained, even for relatively short periods, permanent injury or death can result.
The Queensland research revealed that light and dark coloured vehicles reacted similarly and made little difference to children trapped inside.
According to the Royal Automobile Club of Queensland (RACQ), "the tests also dispelled the widely held theory that leaving the windows down [a little] made the interior cool enough for children. From ambient temperature, the critical 40C mark was reached in a matter of only minutes, even with the windows down 45mm".
The RACQ warns that even when parked in the shade or during the cooler months the car's interior temperatures can become dangerous for infants and children.
The effects of tinted windows and windscreen sunshades were found to make only small differences in cabin temperatures.
The AA advises parents and caregivers to ensure they take their keys with them when they leave their car.
The AA points to instances when children are strapped into their car-seats then given the car keys to play with. They accidentally trigger the remote central locking system, stranding their parents outside.
The Queensland statistics show that accidental lock-ins greatly outnumbered instances where children were intentionally left in a car by unthinking parents. But this may not always be the case.
Research by Drs Guard and Gallagher reported in the journal Injury Prevention examined heat-related deaths to young children in parked cars by analysing 171 fatalities in the United States between 1995 and 2002.
They found that more than 25 per cent of the deaths occurred when parents or other caregivers intentionally left a child unattended in a vehicle.
To avoid child lock-in risks, carers should never use the car as an alternative baby sitter.
* Chris de Freitas is an associate professor in the School of Environment at the University of Auckland.