This scene was constructed as an Audio Test for the Solar Sizzle, damage Stings, the High Damage Alarm, and Full Health. The sounds are coded in the Sira Player Pawn as SoundCues and Audio Components.
When the players first enters the level there is no sizzle since the audio components have not been triggered. If you wanted the sound to fade In as soon as the player entered the level you could do that in the PostBeginPlay Function in the Player Pawn. In this case there is an intro cinematic that plays and there is no sizzle at first so that it doesn't play during the movie.
When the player walks into the first red square they pass through a Volume that triggers a Console Command in Kismet. That command Fades In the Sizzle Sound by Triggering a Fade In Function that can be found in the Sira Player Pawn. In Sira this volume is found when the player first exits the train entering the world.
The Lighter Transparent Red area represents an in-door area. The Player, in Sira, will drop down to a lower level and the sizzle sound should lower as well. This area represents the lower sizzle in the in-door area.
The Player takes Damage from the Sun, in Sira, and when they do the lower sizzle sound fades out and a higher sizzle sound fades in. There is also a damage sting or grunt that can be hurt giving the player feedback so they know that they are getting hurt. If the Player takes too much Damage from the Sun an High Damage Alarm will sound. This sound will stop once the player has regen-ed some of their health. Once the player has regen-ed all of their health another sound is triggered to give the player audio feedback.
The second red square represents going back outside and the Player passes through a volume that's connected to a Switch in Kismet. The first time they go through it the low in-door sizzle fades out and the out-door sizzle fades in. Since in this area the Player can go in and back out and in again this volume will then switch back an forth between triggering the in-door sizzle and the out-door sizzle sounds by triggering those functions in the Sira Player Pawn.