In a study of 20 cases involving serious heat illnesses and deaths among workers in 2012-13, OSHA found that nine out of the 13 deaths occurred as a result of exposure to heat during the first three days of working on the job, with four occurring on the worker’s first day in a new job.

Failure to provide acclimatization of new employees or employees who are returning to work from an absence of more than a week was “the most common deficiency and the factor most clearly associated with death,” the agency said.

OSHA recommends that new workers and workers returning from an absence of more than a week should begin with 20% of the usual duration of work in the hot environment on the first day, increasing the duration of work by no more than 20% each subsequent day.

OSHA also said that during heat waves or rapid temperature increases, employers should acclimatize workers, even experienced ones, by reducing their duration of work on the first day of excessive heat by 50% and slowly increasing the duration of work on the second and third days.

On Aug. 8 Cal OSH proposed expanding its rules to specify that drinking water must be provided at no cost and be fresh, pure and suitably cool, along with spelling out new requirements for shade and cool-down periods and additional worker training Revised written , would be renamed a heat illness prevention plan.

Supervisors also would be required to take immediate action if an employee exhibits symptoms of heat illness, and are prohibited from sending an employee home who exhibits signs or symptoms of heat illness without first offering onsite first aid or providing emergency medical services.