not having a collision with particle

hey guys
i’m having trouble using OnParticleCollision i have a gameobject as enemy which is being hit by a flame particle .i also have counter for enemy health. when the counter gets lower than 0 the enemy body will be set on fire. the problem is that i cant detect that the enemy is no longer colliding with flames.and if the enemy is not colliding with flames i want the counter value to be slowly rest to its original value.
how can i do that?
here is my code.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class particlecolliosn : MonoBehaviour {
	public GameObject fire;
	public int counter = 100;
	// Use this for initialization
	void start () {

	void OnParticleCollision (GameObject collision)

		if (collision.gameObject.tag == "enemy") {


		if (counter <= 0) {
			fire.SetActive (true);
		} else {

			counter = counter;
			fire.SetActive (false);


verify that “105202-captura-de-tela-196.png” is enable.