Every summer, I'll pass a road crew digging up a street in 100-degree heat and suffocating humidity, and I'll think (from inside my air-conditioned car): How on Earth do those guys handle that?

Finally, I decided to look into it, and it turns out that, according to the Occupational Safety and Health Administration, we could do a much better job of protecting those men and women. In 2012, 31 outdoor workers died in the heat and 4,120 fell ill, according to OSHA stats. Over the past 10 years, the average is 36 deaths and 2,810 heat-related illnesses each year. While that's bad enough, OSHA officials think the true numbers are higher, because autopsies aren't usually performed on the victims and many heat-related deaths are listed as heart attacks.

Especially vulnerable are construction crews (can you imagine working on a tile roof in Las Vegas in July?), road workers, farm workers and trash collectors, David Michaels, assistant secretary of labor for occupational safety and health, told me. And among those folks, it's often the temporary worker -- the man or woman called up at the last minute to fill a vacancy on a road crew or trash truck -- who is most vulnerable.

Why? Because they haven't had a chance to acclimate to the heat. OSHA doesn't hand out many citations for heat-related illness -- just 11 were issued last year -- but three-quarters are for not acclimating workers to the heat.

"We tell employers that they have to train workers to know to drink water, to take breaks, but they also have to be given the breaks and they have to be provided the water," Michaels said.

OSHA has put together a disturbing, interactive map of heat-related fatalities as part of its campaign to reduce these needless deaths. (I've included a copy of it above, and here's the link if you want to read some of these horrifying summaries.)

In 2010, a trash truck helper in Puyallup, Wash., began acting irrationally. Emergency responders discovered that his body temperature had reached 108 degrees Fahrenheit. He died at a hospital. In Norfolk, Va., last summer, a worker cleaning a ship's deck collapsed and died on a day when the heat index reached 97. In Medford, Mass., last summer, a mail carrier died of heat stroke after walking his route for five hours carrying a bag that weighed as much as 35 pounds. The area was under a heat advisory.

While the map appears to show the most deaths in hot, populous states such as California, Texas and Florida, Michaels said heat problems disproportionately plague northern states because of the acclimation issue. As anyone who works out in a gym all winter knows, you take it slowly when you first move outside into the heat -- you exercise a little less vigorously, drink more and take more frequent breaks until your body becomes accustomed to the conditions.

But workers under pressure to perform a task sometimes don't have that luxury, especially if they've just been hired or are temporary crew members trying to stay employed.

In 2011, OSHA began a campaign to remind workers and employers of the need for water, rest and shade for outdoor jobs. It followed an intensive effort to protect the tens of thousands of people hired by the BP oil company to clean the shores of Louisiana, Mississippi and Alabama in the intense summer heat and humidity after the Deepwater Horizon spill.

"We didn’t lose a single person from the heat. And I’m sure we would have," Michaels said. "Out of this experience came the realization that this approach should be applied not just in the cleanup. The next year, we started a national campaign to remind employers and employees about the dangers of heat."

OSHA depends on complaints to know when workers are being asked to endure unreasonable conditions, and most situations can be resolved with a phone call or visit from a government official reminding a company about the potential penalties. The agency also has created a smartphone app that tells workers when the heat index is reaching dangerous levels.

Read more: Precautions you should take against summer heat