The invisible threat: thunderstorm asthma

When a thunderstorm rolled into Victoria on November 21, the public was warned to stay away from trees, fallen power lines and flood waters.

The Bureau of Meteorology warned of heavy rain, wind and hailstones but said there was nothing "remarkable".

No one knew the state was under an invisible threat which would push the health system into uncharted territory, claiming nine lives and putting 8500 others in hospital.

At 6pm as Monday commuters made their way home, the Emergency Services Telecommunications Authority - which takes triple-zero calls - experienced a surge from people suffering asthma and respiratory problems.

Less than an hour later, ESTA's target response time of five seconds had stretched to more than four minutes.

Ambulance Victoria's target arrival time of 15 minutes blew out and by 8pm more than 150 callouts were pending, of which 100 were the highest level of urgency - code one.

Police and fire services were responding to ambulance callouts, most of which were code one.

The first public warning of the unfolding crisis came from Ambulance Victoria's twitter account at 8:40pm: "We've seen a rise in breathing probs tonight following the weather. Follow your asthma plan or see here for advice."

Many sufferers had never even had asthma.

A report released on Wednesday by the Inspector-General for Emergency Management, Tony Pearce, details the unprecedented challenge that confronted authorities.

"It was confusing for everybody because we were presented with large numbers of very sick people but with no understanding as to why that was occurring," Mr Pearce told reporters in Melbourne.

The document is not hugely critical of the response, commending services considering the invisible, geographically dispersed, rapid and unfamiliar nature of the health emergency.

But it does say communication between government agencies and emergency services was "inadequate".

Communication was mainly two-way - emails or phone calls between individuals - rather than telephone conferences or group meetings.

The Department of Health and Human Services dealt with hospitals individually, rather than issuing broad information, which, the report said, could have better informed them about the crisis.

And, "little" information was provided to the public during the storm, the report said.

With Mr Pearce by her side, Victorian ambulance minister Jill Hennessy announced $1 million in funding to research what caused the storm and how to forecast similar events.

To aid in forecasting, $300,000 of the money will go to expanding pollen monitoring, currently done at only three sites in Victoria.

The phenomenon of "thunderstorm asthma" is not well understood but the report said it has something to do with extreme levels of grass pollens during a storm.

It is likely triggered by allergens which the wind sweeps up from pollen, which reach peak levels between October and December, and then disperses.