What are the two types of SCSR that contain compressed oxygen?

The correct choice identifies the two types of Self-Contained Self-Rescuers (SCSRs) that are known for containing compressed oxygen, which are M20 and 6.5. This is significant because SCSRs are critical safety devices used in coal mines and other hazardous environments, providing a breathable air supply in the event of dangerous conditions such as smoke or gas exposure.

The M20 is designed specifically for escape scenarios, utilizing compressed oxygen to sustain the user during a potentially life-threatening situation. Similarly, the 6.5 model also employs compressed oxygen, ensuring that miners have a reliable source of breathable air during emergencies.

Both types are integral to emergency preparedness in mining, highlighting the importance of selecting SCSRs that utilize compressed oxygen, which is essential for prolonged escape time and user safety in hazardous situations.