The holiday shopping season is in full swing, and the influx of inexperienced seasonal workers, an avalanche of orders and tight delivery timelines can make fulfillment centers a more precarious and tiring environment for workers this time of year, experts say.

The holiday season is a “pretty intense time” for fulfillment centers, and the increased pressure can lead to more soft tissue injuries and car accidents, said Chris Hayes, Hartford, Connecticut-based second vice president of transportation, risk control at Travelers Cos. Inc.

Although monthly federal data on injury rates specifically at fulfillment centers is not available, reports of alleged injury rates at several Amazon.com Inc. fulfillment centers have garnered attention. On Monday, 42 lawmakers in New York, which included state senators, assemblymembers and city council representatives, drafted a letter to Seattle-based Amazon over “incredibly disturbing reports of dangerous working conditions” and worker injury rates in the company’s Staten Island, New York, warehouse.

Warehouse injuries for retailers catering to holiday shoppers “absolutely” increase in the months leading up to Christmas, often as a result of seasonal workers brought on to meet demand, said John DeRoia, a Cromwell, Connecticut-based safety management consultant for The MEMIC Group.

“You can expect to see up to doubling of the workforce for two months,” he said, adding that workers may be more likely to sustain injuries if they don’t know how to do the job or don’t understand the training, or if employers fail to provide sufficient new-hire training.

“Eleven months of the year, we run well-organized machines of safety management, but pressure drives decisions in this period,” said Woody Dwyer, second vice president of workers compensation, risk control at Travelers, also based in Hartford.

According to the U.S. Bureau of Labor Statistics, recordable injury and illness rates in warehousing and transportation — which include fulfillment centers — has declined slightly in the past five years to 4.5 injuries and illness per 1,000 workers in 2018 from 4.7 in 2013, but with the job growth in this sector, recordable injury rates climbed to 213,000 in 2018 from 192,000 in 2013.

During the holiday shopping season, many hazards place warehouse workers at risk, including forklifts overturning or running off warehouse docks, improperly stored merchandise and improperly lifted boxes, and seasonal workers’ unfamiliarity with seemingly common tasks, said a U.S. Occupational Safety and Health Administration spokeswoman in an email Tuesday.

Fatigue during the season is another significant contributor to fulfilment center injuries, said Deborah Roy, Falmouth, Maine-based president of SafeTech Consultants Inc. and recently retired corporate director of health, safety and wellness at Freeport, Maine-based clothing retailer L.L. Bean Inc.

As hours worked increase, injury rates also increase, regardless of whether the workers are seasonal or year-round employees, said Ms. Roy, who is also president-elect of the Park Ridge, Illinois-based American Society of Safety Professionals.

“The research shows that any consistent workload above 60 hours a week over time does impact injury rate,” she said. “No matter how well a job is designed, if you’ve pushed the human body past its ability from a fatigue standpoint, you’re increasing the likelihood of injury.”

To mitigate the risk of injury to seasonal and seasoned workers, L.L. Bean kept tabs on worker hours and had conversations with those who appeared fatigued or working close to or above 60 hours a week to encourage a day off, said Ms. Roy. The company also recently implemented a pilot using athletic trainers and physical therapists on the floor to watch seasonal employees and tweak or correct the way they performed their jobs before bad habits that put them at risk of injury could be developed, said Ms. Roy. These changes had a positive impact on workers compensation claims, she added.

At Amazon, a company spokesman said in an email on Thursday that Amazon’s recordable injury rates for its more than 150,000 North American associates may be “misleading” because of its “aggressive stance on recording injuries no matter how big or small.”

The company also invests “heavily” in safety, and tracks and audits leaders to ensure they “continually improve the safety results of their operations,” the spokesman wrote. “We keep safety front and center in our fulfillment centers and top-of-mind in our daily operations.”