According to various guidelines and standards for designing a computer forensics lab, including the International Association for Identification (IAI) and the American Society of Crime Laboratory Directors (ASCLD), a computer forensics lab should have a minimum of two exits.
This is to ensure that:
There is a primary exit for normal use.
There is a secondary exit for emergency situations, such as a fire or other hazardous conditions.
Having two exits also helps to prevent evidence contamination and ensures a safe and secure environment for examiners to work in.
So, Steven should include at least two exits in his design for the computer forensics lab.