The discovery of Tannerite in the improvised bomb that injured 29 people on Saturday in New York is focusing attention on a brand-name explosive that is widely available in Canada and the U.S.

On Sunday, a federal law enforcement official said the Chelsea bomb contained a residue of Tannerite, an explosive often used during target practice that can be picked up in many sporting goods stores. The discovery may be important, as authorities probe the source of the bomb.

Tannerite is a binary explosive, meaning it is created by mixing two powders — ammonium nitrate and aluminum powder — in a combination the manufacturer says is patented.

Rifle shot needed to detonate

Both these substances are safe and stable by themselves. They are only explosive when mixed together. When Tannerite is shipped or purchased, the powders are separate and only mixed together just before use.

Tannerite is used to create an exploding target in shooting practice, showing the shooter whether the target has been hit at long range.

Tannerite detonations only occur when the target is hit with a bullet at high velocity, producing a large explosion and cloud of water vapour, according to the manufacturer's website.

The makers recommend a bullet travelling at 600 metres per second or more to detonate the target.

It is not yet known how the explosion on 23rd street in New York on Saturday was detonated. No traces of Tannerite were found at the site of the blast in New Jersey.

Cellphones were found at the site, but Tannerite cannot be detonated with a fuse unless the explosive is altered in some way, according to the manufacturer.

Widely available in Canada, U.S.

The product, available since about 2000 in the U.S., is widely available in sporting goods shops throughout the U.S. and both online and in retail shops in Canada. It is legal, though there are restrictions on where it can be used.

The Tannerite manufacturer's site says Canadians must have an explosive importation permit from Natural Resources Canada before the company can ship to Canada. But there are Canadian retailers who carry the product.

According to Natural Resources Canada, binary kits in this country are "subject to federal laws" and buyers must meet specific requirements.

Tannerite is supposed to be mixed in small amounts — about half a kilogram to a kilo at a time — and the manufacturer recommends standing at least 90 metres from the target when shooting.

The manufacturer also recommends against having other debris or material near the explosive as it is shot.

The product comes with warnings it is dangerous if misused. An expert told The Associated Press that a lot of Tannerite would have to be used to cause an explosion the size of the one in New York.

However, YouTube videos show enthusiasts using much more than the recommended amounts, with both automobiles and a barn blown up with large amounts of the binary explosive.