apache server hangs php-cgi, how can i debug further

We have Windows Server 2012 R2, Apache 2.2.31 and Php 5.6.18, Zend Server Version: 8.5.3

Apache seems to be hanging more and more frequently, a restart of apache seems to fix the problem most times. There are a quite a few php-cgi's open when we look at the the process viewer.

Windows event viewer shows multiple events like this,

18 JUL 2016 09:13:23
Faulting application name: php-cgi.exe, version: 5.6.18.0, time stamp: 0x56b9d4d2
Faulting module name: php5.dll, version: 5.6.18.0, time stamp: 0x56b9d4ce
Exception code: 0xc0000005
Fault offset: 0x002f8a02
Faulting process id: 0x1550
Faulting application start time: 0x01d1dfad0acd3f1b
Faulting application path: C:\Zend\ZendServer\bin\php-cgi.exe
Faulting module path: C:\Zend\ZendServer\bin\php5.dll
Report Id: e05b4091-4cc7-11e6-80bb-002590634814
Faulting package full name: 
Faulting package-relative application ID:

What things can i do to debug this further so I can figure out what is going wrong?

A user reports a similar exception (0xc0000005) on stackoverflow which suggests that the problem is a memory access error, and the code accesses a nil pointer (or is blocked from access for protection reasons..);
https://stackoverflow.com/a/31535903/329931

Their remedy is to disable the EMET features on the binary exe. There is some information on disabling EMET features for specific applications here;
http://windowsitpro.com/security/using-emet-disable-specific-applications

If you are not running EMET, or that does not fix your problem, there is also a newer version 8.5.5 of Zend server which might include a bugfix;
http://www.zend.com/en/products/server/downloads#Windows

and newer versions of php since 5.6.18 (current 5.6.22); http://windows.php.net/downloads/releases/archives/