Charges Against Philly Demo Worker Underscore Complexities of Legal Pot

Accusations that the operator of the excavator that led to the deadly building collapse in Center City last week was high on marijuana raise compelling questions about how governments will regulate pot as states continue to decriminalize its use.

Prosecutors charged 42-year old-Sean Benschop with six counts of manslaughter after a toxicology test showed he was “unfit to perform safety-sensitive, job-related duties” due to the presence of marijuana in his blood stream. (The test also identified the presence of unspecified painkillers, which may or may not have been prescribed to him and may or may not have affected his ability to safely demolish a building.)

Since his arrest, witnesses have come forward to lend support to the claim that Benschop was high on the job. That’s good news for the D.A.’s office. Because, when it comes to marijuana impairment, forensic evidence alone is notoriously unreliable, and—if Benschop’s defense attorneys are worthy of the name—would be unlikely to convince a jury that he was intoxicated at the hour the Salvation Army Thrift Shop at 22nd and Market Street came crashing down.

Unlike alcohol, there is no equivalent to the Breathalyzer to gauge pot intoxication, so investigators typically use a combination of observational data, intuition and, in many cases, a blood test to construct evidence that a suspect is high. But almost all experts agree that the results of these tests are inadequate for determining if a person was actually impaired at the time the blood was drawn. Not only is there no universally accepted intoxication-threshold for tetrahydrocannabinol (THC)—the active ingredient in marijuana—in the blood, even if there was one it would be subject to challenge.

For the most part, the chemistry of marijuana remains a mystery, and its effect on humans varies greatly from person to person. THC is stored in fat cells, and it can be detected in the body anywhere from days to months after smoking depending on a variety of issues, such as frequency of use, drug potency and individual physiology. All these factors make THC levels a poor metric for proving that a person was under the influence of marijuana at the time they were driving/operating machinery. (Philly Mag’s Nick Vadala explored this topic in detail last year in reporting on the case of Max Drosi, who was charged with vehicular homicide after a blood test showed he had THC in his system when he crashed his car into a small crowd of people at the Italian Market, killing an 11-year-old. Drosi claimed he was distracted by his GPS device.)

Drosi’s case is scheduled to go before a jury in January 2014, and prosecutors will no doubt rely on blood evidence to show the defendant was high at the time of the accident. If the federal government is to be believed, the evidence shouldn’t be too hard to challenge. According to the U.S. National Highway Traffic Safety Administration (NHTSA):

“It is difficult to establish a relationship between a person’s THC blood or plasma concentration and performance impairing effects. Concentrations of parent drug and metabolite are very dependent on pattern of use as well as dose. It is inadvisable to try and predict effects based on blood THC concentrations alone…”

Because the science is so elusive, laws governing stoned driving vary greatly from state to state—with most states relying on non-forensic variables, like observation and field sobriety tests, to prove impairment. Pennsylvania is one of just 16 states that impose so-called per se limits on the amount of allowable THC in drivers’ blood; and with the exception of the 11 states that have zero-tolerance policies that prosecute for any trace of THC, it maintains the lowest threshold for legal intoxication of any other per se state. In 2011, lawmakers in Harrisburg passed a bill reducing the THC threshold for driving under the influence from five nanograms per milliliter (ng/ml) to just one ng/ml—so low that the commonwealth may as well be a zero-tolerance state. According to research, it’s not unheard of for blood to reflect THC levels of five ng/ml up to four hours after use, when most experts agree a user’s high has largely worn off; and heavy users can show THC levels as high as three ng/ml up to 12 hours after smoking.

Washington and Colorado, which both recently voted to legalize weed, are already grappling with the complex issues surrounding its regulation. Foremost among them is how to legislate driving while stoned. In April, the Colorado Senate rejected for the fourth time a bill to establish a legal impairment level of five ng/ml due largely to the lack of reliable research on THC intoxication.

“We are being asked to make policy by anecdote,” said Republican Senator Shawn Mitchell, a critic of the bill.

A similar measure passed last year in Washington over the objections of some legal experts that replaces “demonstrated impairment” with a per se threshold of five ng/ml; and in Oregon, where voters may get a second chance next year to approve legal recreational weed, battle lines are already being drawn over possible new drugged-driving statutes (Oregon currently has no per se limit on THC in the blood). Meanwhile, a court in Michigan recently ruled that that state’s per se drugged-driving law cannot be used to prosecute patients who are prescribed medical marijuana.

If the absence of reliable science on THC levels and intoxication isn’t bad enough, there is just as little data on just how much marijuana actually impairs driving judgment; and much of what is around suggests that it might not have much of an effect at all. A number of government-funded studies in the U.S., the Netherlands, Australia and Britain—including this one from the Department of Transportation—have shown that at least when it comes to driving a vehicle, pot has the opposite effect as alcohol, and actually makes people more cautious on the road.

Putting that question aside for the time being, it’s clear that more research is needed to develop a reliable and universal standard for THC intoxication. Ironically, while public sentiment towards recreational marijuana use is evolving, thanks to prohibition, the official science surrounding pot impairment is stuck in the dark ages and doesn’t appear to be getting any better. In the absence of adequate science, courts should consider throwing out unreliable blood evidence of THC intoxication and require criminal investigators to prove drivers were demonstratively impaired at the time of their arrest.