Introduction

When firefighters work in the heat, they experience increases in platelet numbers (a clotting agent), thus increasing the likelihood of cardiovascular event, the most prevalent cause of line-of duty injury and fatality. Levels of platelet activity are particularly relevant if levels remain elevated prior to beginning subsequent work shifts. However, the extent of changes to platelet numbers after an overnight rest, such as during multi-day deployments is poorly understood. Thus, this study aimed to assess changes in platelets of firefighters 24-hours after a work bout in the heat.

Methods

Forty-two urban firefighters completed two twenty-minute search tasks in the heat (100 ± 5°C). Based on standard operating procedures for an Australian fire service, participants had a ten-minute recovery outside the heat chamber between work bouts, where they consumed 600 ml of water. Core temperatures (T_c) and heart rates (HR), along with platelet and white-blood cell numbers were evaluated following work and also following one and twenty-four hours of rest.

Results

Increases in T_c (+1.4 ± 0.5 °C) and high HRs(90.9 ± 7.1 % HR_max)were observed following the second work bout. Platelet numbers were significantly increased post-work, and continued to increase during one hour of passive recovery (+31.2 ± 31.3 10^9L). Further, platelet numbers remained elevated up to 24 hours later (+15.9 ± 19.6 10^9L).

Discussion

The work protocol, reflective of standard work practices in urban fire services, resulted in significant increases in T_c and HR along with acute changes to platelet numbers. However, of greater concern is the ongoing elevation in platelet numbers after a 24-hour period of rest. Any residual elevations in platelet numbers after extended rest may be increasing the risk of thrombotic events when firefighters work over multiple days in adverse environmental conditions. Appropriate rehabilitation protocols may ameliorate these increases but this remains unclear