A day after the attacks in Brussels, airports around the world were once again facing intense questioning over their security measures.

On Tuesday, two suicide bombers detonated explosives in Zaventem Airport, in suburban Brussels, while another blew himself up in the city's subway system. The attacks resulted in the deaths of dozens of people and wounded more than 270 others.

The airport attacks occurred in a check-in area with only limited security.

The fact that the bombers could move freely towards their target, and that there is often little scrutiny of passengers before pre-boarding screening, has drawn criticism from experts.

Like Brussels, North American airports usually focus most of the security after passengers check in.

"When you go into airports in Canada, you will see that you enter a terminal full of people and nobody looking at you, nobody testing you, nobody seeing if you (have) an intent to harm the people," said Rafi Sela, an airport security consultant.

In countries like Israel, the screening begins in the parking lot, where staff trained in behavioural analysis can intensively question travellers to elicit signs of suspicious behaviour.

Raphael Ron, former security director of Ben Gurion Airport, said this technique might have kept the Brussels attackers from reaching their targets.

"It should have led the trained eye to respond at least by approaching those people on the curbside already and trying to figure out who they are," said Ron.

Some countries have also introduced secondary layers of security at airports, including mandatory screenings of travellers and baggage at building entrances, as well as cars, taxis and buses.

In addition to Israel, these methods have become common practice in Russia, as well as large parts of the Middle East and some countries in Africa.

But a national approach to airport security in Canada may be difficult.

The Canadian Air Transport Security Authority, which is a Crown corporation responsible for overseeing security screening in the country's 89 designated airports, said individual airports are responsible for the "public spaces" in front of their check points.

With a report from CTV's senior political correspondent Glen McGregor