ParticleEmitter help

I have attached two particle emitters to a bone of a gameobject. I want to enable or disable them upon predefined events having them turned off on start.
Please find here my initialisation function.

Code (csharp):

1.  
2. function Start () {
3.    
4.     var _particles : Component[] = GetComponentsInChildren(ParticleEmitter);
5.    
6.     for (var p : ParticleEmitter in _particles)
7.     {
8.         p.emit = false;
9.     }
10.    
11.     while(true){
12.         for (var p : ParticleEmitter in _particles)
13.         {
14.             if(partEmit){
15.                 p.emit = true;
16.             }
17.             else{
18.                 p.emit = false;
19.             }
20.         }
21.         yield;
22.     }
23.    
24. }
25.  

The error that I get states that the particles have been destroyed and therefore I can no longer access them.

Could somebody kindly suggest the best practice to achieve this?

Many thanks.