Yes, they do. They always have been required but prior to 2015 there was nothing in B149.3 to say how to do it. There are now clauses in the main body of the code and an annex at the end of the code.
Are there any exclusions?
Only process flows are excluded from the Codes although from a safety perspective they still must be interlocked to the system one way or another. Translating this to the flare stack, ground flare or incinerator world the pilot or sustaining natural gas burners and their trains must comply with the Code, but the waste gas stream does not. This is assuming that the waste gas stream by itself is not a fuel but that it needs some other fuel to produce "thermal energy" to help dispose of the waste gas.
Is there a distinction between "Process" and "Emergency/Safety" flares?
Process flares are appliances which burn off waste gases from the process. If a flare goes down so must the process. It is only a question on how to shut the site down safely, and how long should the site be allowed to vent the process gases without igniting them before either a harard is created or an environmental permit is violated. The less time for shutdown is allowed, the more robust required for the flare solution, including multiple pilots, constant re-ignition, etc. Bottom line, with process flares, failure of the flare leads to plant shutdown.
Emergency flares are considered to be "the last line of defense" type of appliance which MUST work in case of plant emergency (such as overpressure) and which cannot be shut down or cannot cause the shutdown of the plant or process. Hence, the emphasis with emergency flares is to make sure that they NEVER fail. This can be accomplished by multiple pilots (per AOI), multiple fuel sources, multiple power sources, etc.
In both cases (emergency and process flares) there are still critical permissives to be considered, such as: - fuel gas pressure LOLO (pressure below which flare will not function or will not be effective in lighting the main gas - fuel gas pressure HIHI (pressure above which flare pilot may become unstable or blow off the tip) - fuel gas pressure LO (low pressure alarm before the pressure gets to LOLO trip point - fuel has pressure HI (high pressure alarm before the pressure gets to HIHI trip point. - flame failure trip or alarm - etc. The idea of flare protection is that of multiple levels of redundancy, which in the case of process flares delays the total failure of the flare system until the process can be shut down, and in case of emergency flares ensures that the flare never fails.