Since 2018 Israel has been dealing with a new threat coming out of Gaza, where Hamas and other Islamic terrorist groups are regularly coming up with new ways to attack Israel. The latest one is helium filled balloons carrying small explosives or incendiary devices across the border into southern Israel. So far several thousand of these balloons have been used, most of them to carry incendiary devices that ignite when the balloon hits the ground. The prevailing winds in the area go from Gaza towards Israel and the Gaza “arson balloon” makers have, through trial and error developed a balloon based aerial weapon that uses several helium filled balloons carrying a lightweight (about half a kilogram/one pound) incendiary device that will eventually come down in southern Israel. Kites are also used but these are less effective than the helium balloons.
Since early 2018 these balloons have started nearly 700 fires, which burned 910 hectares (2,260 acres) of forest and grassland as well as 619 hectares (1,500 acres) of farmland, much of it with unharvested crops. None of these balloons has landed more than 40 kilometers from the border. Others may have been lost at sea. Despite Israeli retaliation attacks, using artillery, helicopter gunships, UAVs and F-16s, the arson balloons keep coming.
Israel has also sought to halt the import of arson balloon components, especially the balloons and helium gas. Most of the foreign aid and imports going to Gaza are inspected at an Israeli checkpoint. The problem is that packs of uninflated balloons don’t take up much space and the balloons can be hidden among other items. Some balloons have been seized at the border, but not enough. The helium is easier to detect because the only helium that is legally sent to Gaza is liquid helium used to cool the magnets on the six MRI medical scanners in Gaza. When in use the MRI scanners use up some of the liquid helium. If all the MRI machines are used regularly Gaza would require no more than 100 (220 pounds to 300 kg/(660 pounds) of liquid helium a month. Israeli surveillance UAVs have video of Hamas operatives filling balloons from natural gas canisters, apparently reused to carry helium gas. It would only take a few kg of liquid helium to produce enough helium gas to fill over a thousand balloons. As a result, Hamas does not have to smuggle helium gas into Gaza. Instead, Hamas diverts small amounts of the legally imported liquid helium. The amount needed for the arson balloons transferred, is gas form, to empty natural gas cannisters that are used for cooking in Gaza. This is a classic application of “dual-use” civilian materials to military use.
Israeli efforts to detect and destroy the balloons before they could land in Israel have not resulted in a perfect weapon. But several systems were effective and this contributed to work on systems to detect and destroy quad-copters and other small UAVs equipped with explosives making more precise and deadly attacks. The arson balloons have not killed anyone yet but it's only a matter of time until some form of defense can detect and destroy most of the arson balloons. Israel has developed sensors (optical and radar) that can do this, as well as short range lasers powerful enough to disable small UAVs and destroy arson balloons that are a kilometer or more distant.