Still fearing a market freefall like the big one on Black Monday back in 1987? Cautious market pros say never say never.

Still, keep your emotions in check, as this isn't a déjà vu market -- even though investors might have gotten spooked by the Dow Jones industrial average's brief early drop of 105 points today on the 30th anniversary of the 1987 stock market crash. At midday Thursday, the Dow was down just 45 points or 23,112 -- a far less than 1% decline. 

Today's stock market has some built-in shock absorbers designed to slow down a  meltdown that it didn't have 30 years ago when Ronald Reagan was president and the Dow fell 508 points, or 22.6% -- in a single day.

Back in 2012, Wall Street's top regulator revised so-called "circuit breakers," to help slow the descent of the stock market on days it was in freefall. Simply put, the circuit breakers are a mechanism that shuts down the market temporarily after dramatic drops.

**FILE** Traders on the floor of the New York Stock Exchange work frantically in this Oct. 19, 1987 file photo as the Dow Jones Industrial average plunged more than 500 points for a loss of 22.6%, Wall Street's worst day ever.

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Here a few reasons why a 1987-style crash might not occur or play out the same way today:

Circuit breakers slow fall

Under the circuit breaker rules, market-wide trading halts are triggered if the Standard & Poor's 500 stock index falls 7% (Level 1) or 13% (Level 2) or 20% (Level 3) from the index's prior night's close. 

If drops of 7% or 13% occur before 3:25 p.m. a 15-minute market-wide trading halt will kick in. If similar declines come at or after 3:25 p.m. no halt will occur. However, if a market drop of 20% triggers a Level 3 circuit breaker at any time during the day, trading will be shut down for the rest of the day.

"The idea of the circuit breakers is to bring short-term stability to the stock market and prevent fear and panic from snowballing," explains Joe Quinlan, chief market strategist at U.S. Trust. 

2017 market measures are solid

Today's market hasn't raced ahead quite as fast or exuberantly as stocks did leading up to the 1987 crash. What's more, today's interest rates are far lower and less threatening to stock valuations than back in October 1987 when the 10-year Treasury yield was 10%, vs. today's yield of 2.3%. Corporate earnings have also been strong, which is another pillar of support for stocks.

Global economy in rebound mode

The U.S. economy is also in solid shape, as is the global economy, where virtually every country around the world is seeing an uptick in economic growth. 

 

Investors have learned from past crashes

Investors haven't forgotten the 1987 meltdown or the more recent "Flash Crash" in May 2010 that sent the Dow spiraling down 600 points in minutes and almost 1,000  points on the day before recouping the bulk of its losses. 

"It makes me much more aware of tale risks, which is a good thing," says Brad McMillan, chief investment officer at Commonwealth Financial Network.

McMillan won't rule out another crash one day, noting that investor complacency is high at the moment and "now as then, investors really believe markets are low risk and that returns are more or less ensured."