# Setting up the second stage of the sparks effect

For a realistic simulation, the sparks need to appear randomly, not in a single steady stream. At the same time, the sparks need to appear to be produced by the collision between molten slag and the cooler slag chute. Creating too many sparks can easily make the simulation look too staged and unrealistic.

To create these conditions, you might use particle expressions, but in this lesson you will use only nParticle attributes. This means that only a few particles are required and they must appear stationary at various locations along the chute. Also, they must not self-collide nor be visible in the simulation, but still participate in the effect.

1. In the Outliner, select the nParticle_sparks_emitter and in the Attribute Editor, click the nParticle_sparks_emitterShape tab.
2. In the Lifespan section, set the following:
   - Lifespan Mode: Random range
   - Lifespan: 0.1
   - Lifespan Random: 1.0

   Since this nParticle object needs to be in the scene just long enough to emit a burst of sparks, you give it a short Lifespan.

3. In the Collisions section, turn off Self Collide.

   Although the individual nParticles in this system will not be close enough to collide, turning off Self Collide saves the Nucleus solver from calculating these collision iterations.

4. In the Emission Attributes section, set Emission Overlap Pruning to 10.

   This attribute keeps nParticles from self-colliding while being emitted. A value of 1 guarantees that no self collisions occur with other particles on emission. This value ensures that only a few, evenly spaced particles are emitted from the collision event.

5. Rewind and play the simulation.

   A good number of particles are created on the chute, spread out evenly along its length. Notice however that the particles move down the chute with the slag. Since these nParticles will emit other nParticles, they need to remain fixed to the chute.

   NOTE:To make it easier to see where on the chute the new nParticles are, and how many are being emitted into the scene, set the scene shading to Wireframe.
6. In the Dynamic Properties section, turn on Ignore Solver Gravity.
7. Rewind and play the simulation.

   With gravity disabled on the object, the nParticles remain fixed at various along the slag chute. These locations will emit the nParticle sparks.

8. To ensure that these particles are not visible in the scene, in the Shading section, set Opacity to 0.

   Next, you will create and adjust nParticles to simulate the flying sparks.