As long as you remain in the transit area of the airport, you do not need a visa as an Indian citizen in Belgium (or any Schengen country except France, Germany, Spain and the Czech Republic), even if you need to disembark and catch a connecting flight. This should also apply to any unexpected need to leave the airplanes in your case. If you would need an airport transit visa, the US visa could help but it does not apply here since you can in any case transit without a visa.
All this only applies if you have only one layover in the Schengen area, in an airport with a proper transit area. If you have two layovers with an intra-Schengen flight in between (like the previous question about Vienna and Frankfurt) or if you need to change airports or otherwise leave the transit area, you need to have the right to enter the Schengen area. In this case, the rules for entry (as opposed to transit) would apply. Consequently, an airport transit visa would not be enough (you need a full Schengen visa) and the exemption for US visa holders does not apply either.
There are also provisions to grant a visa-on-arrival in extraordinary circumstances (say an emergency landing at an airport with no transit facility) but in normal circumstances, it's not possible to get a visa-on-arrival. If you normally need a visa for your trip (whether a regular type C visa or an airport transit visa), then it needs to be obtained in advance. Airlines have to check your visa and would refuse boarding if you don't have the documentation needed for your transit.