Ontarians placed more than 32,000 orders for iodide pills in the two days following a false alarm about an incident at Pickering Nuclear Generating Station.

There are normally between 100 and 200 orders per month, according to Ontario Power Generation.

But after an alert warning of an unspecified problem at the nuclear facility was sent in error Sunday morning, there were 32,388 orders placed over that day and Monday.

In Ontario, potassium iodide (KI) pills are distributed to residents within 10 kilometres of a nuclear facility; others living within a 50-kilometre radius of one can order them through a website called preparetobesafe.ca. In New Brunswick — the only other province with an operating nuclear power plant — the distribution radius is 20 kilometres.

The pills help protect the thyroid gland and reduce the risk of cancer if radioactive iodine is released into the air in the unlikely event of a nuclear emergency, according to the Canadian Nuclear Safety Commission. They saturate the thyroid gland with non-radioactive iodine and prevent radioactive iodine from being absorbed.

“The thyroid gland will absorb iodine that is in a person’s bloodstream; it cannot tell the difference between radioactive iodine and non-radioactive (stable) iodine,” the CNSC says.

“The absorption of radioactive iodine can be prevented by taking KI before or soon after its release into the air.... Over time, the radioactive iodine will undergo radioactive decay and be harmlessly excreted in urine.”

The risk of side effects is “extremely low,” according to the preparetobesafe website, which is operated by Durham Region, the City of Toronto and Ontario Power Generation. Rare and mild side effects include gastrointestinal issues or hypersensitivity reactions, and people with thyroid disorders are at a greater risk of side effects.

People should only take the pills if directed to do so by public health officials, CNSC says. They are considered to last for up to 12 years as long as they are stored in a dry location that is kept between 15 C and 30 C.

Ontario has launched an investigation into the false alarm, and Solicitor General Sylvia Jones has said it won’t be a long and drawn-out probe.

Initial observations suggest human error was responsible for the message that was sent out during routine tests of the emergency alert system, Jones said.

A follow-up alert with an all-clear was sent to cellphones nearly two hours after the original notification.