List<BMCServiceDesk__Incident__c> iShareList = [[SELECT id, BMCServiceDesk__Client_Manager__c FROM BMCServiceDesk__Incident__c WHERE (Equipment_Request__c= true OR Manager_Approval__c = true) AND Id IN: trigger.new];

IncidentSharing.manualShareRead(iShareList);

public class IncidentSharing {
   
   public static boolean manualShareRead(List<BMCServiceDesk__Incident__c> iShareList){
   	
 	  // List of Shares to insert  	
   	  List<BMCServiceDesk__incident__Share> incShrList = new List<BMCServiceDesk__incident__Share >();
   	  
   	  for(BMCServiceDesk__Incident__c i:iShareList){   	  
	      // Create new sharing object for the custom object Incident.
	      BMCServiceDesk__incident__Share incShr  = new BMCServiceDesk__incident__Share();
	       
	      // Set the ID of record being shared.
	      incShr.ParentId = i.Id;
	        
	      // Set the ID of user or group being granted access.
	      incShr.UserOrGroupId = i.BMCServiceDesk__Client_Manager__c;
	        
	      // Set the access level.
	      incShr.AccessLevel = 'Read';
	        
	      // Set rowCause to 'manual' for manual sharing.
	      // This line can be omitted as 'manual' is the default value for sharing objects.
	      incShr.RowCause = Schema.BMCServiceDesk__incident__Share.RowCause.Manual;
	      
	      // Add share to list
	      incShrList.add(incShr);
   	  }
        
 
      // Insert the sharing record and capture the save result. 
      // The false parameter allows for partial processing if multiple records passed 
      // into the operation.
      Database.SaveResult[] sr = Database.insert(incShrList,false);
      
      // iterate through each returned result      
		for (Database.SaveResult sr : srList) {
		    if (sr.isSuccess()) {
		        // Operation was successful, so get the ID of the record that was processed
		        System.debug('Successfully inserted account. Account ID: ' + sr.getId());
		    }
		    else {
		        // Operation failed, so get all errors                
		        for(Database.Error err : sr.getErrors()) {
		            
		        }
		    }
		}
 
      
   }	
}