The history of SSC lies in the gay S/M scene in the 1980s as a reaction to consent concerns in the community and in response to opinions in mainstream culture that gay S/M was psychologically harmful and connected to violent crime.

The phrase was supposedly coined by members of the New York Gay Male S/M Activists (GMSMA). It was a combination of “consent,” which many BDSM voices at the time were already emphasizing, and “safe and sane.” The latter part of the full meaning of the acronym had roots in the popular July 4 saying, “Have a safe and sane Fourth of July” and was championed by Tony DeBlase, a renowned BDSM educator and publisher.

SSC became the term for describing keeping your kink activities on the right path.

People who follow the SSC method of BDSM safety measures usually make sure they answer three questions:

• Is our kinky thing safe to do?
• Is it a sane thing to do?
• Do we consent to it?

For SSC to be in motion, both partners have to establish what is safe and what is sane. This method works best when both partners are on the same page, feel the same way about certain kinky activities, and have a similar ideology about kink.

Jay Fin on Quora gives his opinion;

In my opinion, "Safe, Sane and Consensual" in a BDSM/Kink context is insanity, simply because (most, not all) BDSM/Kink activities are not safe, at least in the sense that nothing can really go wrong. Bondage can go wrong and cause nerve damage, the same goes for a heavy spanking, use of a bull whip and those are just the “basics” of things one can undertake in a BDSM/Kink relationship.

Sometime around the early 2000s, some members of the BDSM community found some gaps in the SSC method. Check out some of their reasons:

• According to them, nothing in life is 100 percent safe, especially activities that can, and often do, involve injury. There is no such thing as a “guaranteed safe way” to engage in some BDSM activities.
• Also, people have different views. Therefore, what is “sane” to one person might be "insane" to another. The term cannot be generalized.
• The ever-evolving nature of people's interests and limits make the concept of SSC insufficient to describe a person's expectations and limits within the BDSM community.
• “Safe” and “sane” are terms that make BDSM look 'nice' to people outside the community but do not adequately represent BDSM for people who partake in it.

IntheGoatshow on Reddit says;

At some point, I think we have to acknowledge that everything we do carries a degree of risk, and the trust and vulnerability required by kink will, by its very nature, heighten that risk.

However, despite these differences and limitations of SSC, the delicate nature of the BDSM community requires that everyone strives to understand each other whether everyone's limits and interests align or not.

This is why the SSC method, which is highly limited by the different  opinions, interests, and limitations of the community, is simply an inadequate description of what can be considered generally acceptable in the BDSM community.

Given this, the philosophy of Risk Aware Consensual Kink (RACK) was established in the community.

The acronym, RACK means Risk-Aware Consensual Kink. It was created as a response to those who felt that SSC was too vague, confusing and insufficient to capture the entire opinions and interests of people in the BDSM community.

• Risk-aware: RACK emphasizes that you should go further than just knowing risks. You should know how to prevent them.
• Consensual: Everyone must be on board and in agreement with what you’re about to do or what you’re currently doing.
• Kink: The BDSM activity, power exchange, scene, or play.

RACK answers questions such as; Whose version of “safe” or “sane” are we concerned with? What if one partner thinks one thing is sane but the other thinks it is irrational ? Who wins that argument?

If you’re new to RACK, use this like a checklist for your BDSM play; Can you name the risks? Are you both able to affirm your consent to each other? Do you understand exactly what event/activity is about to take place?

On the part of people who address the 'safe, sane and consensual' philosophies, there is always the misconception that people engaging in BDSM must follow either the SSC or RACK method.

However, the reality is that they should and must be used in tandem, as separate, but complementary terms to describe the opinions, interests, ideologies and limitations of both partners.

Safe, Sane, and Consensual (SSC) can only truly be followed by people who have first understood Risk Aware Consensual Kink (RACK). This is because it is the awareness of the risks involved that will make a situation safe or unsafe and sane or insane. It is the communication and shared interests between partners that will create the air of consent and the pleasure of experiencing kink.

We recommend considering both measures in this manner; whenever you go out of your safe-zones, RACK is a reliable guideline. Then when you become aware and comfortable with a kink activity, it can then fall into what you would consider safe, sane and consensual.

The understanding and acceptance of kinks that are not in alignment with your own kinks remain one of the challenges of the BDSM community. Applying both SSC and RACK as safety measures solve this problem to a great extent. Good luck in your future BDSM engagements.