I saw that some instances of apache die in a segmentation fault.
I found this errors in core dump of apache.
#0 0x00002b180e623820 in crc32 () from /usr/lib64/libz.so.1
-------------------------
#0 0x00002b180e623820 in crc32 () from /usr/lib64/libz.so.1
-------------------------
#0 0x00002b180e623820 in crc32 () from /usr/lib64/libz.so.1
-------------------------
#0 0x00002b180e623820 in crc32 () from /usr/lib64/libz.so.1
-------------------------
#0 0x00002b180e623820 in crc32 () from /usr/lib64/libz.so.1
-------------------------
#0 0x00002b181603e3a9 in ?? () from /etc/httpd/modules/libphp5.so
-------------------------
#0 0x00002b180e623820 in crc32 () from /usr/lib64/libz.so.1
-------------------------
#0 0x00002b180e623820 in crc32 () from /usr/lib64/libz.so.1
-------------------------