The risks of carbon-monoxide (630080) (CO) exposure in aircraft refueling operations are reviewed. Deaths among workers who fuel jet aircraft are cited. Investigations of incidents are described in which a combination of unusual location of engine exhaust, deterioration of rubber seals around the gear shift lever and pedals, and time spent by workers in idling vehicles resulted in dangerous CO concentrations in the truck cabs. CO is a colorless, odorless, gas that limits the ability of the blood to carry oxygen to the tissues. Symptoms of poisoning include headaches, rapid breathing, nausea, weakness, dizziness, confusion, hallucinations, and discoloration of lips and nail beds. Recommendations for control of CO hazards in refueling operations include: conversion of trucks to electric or diesel power; prevention of entry of CO from beneath the cab in refueling trucks; tuning of engines; installation of continuous CO monitors in truck cabs; provision of comfortable waiting areas to avoid waiting in idling truck cabs; restrictions on smoking among workers; and interim work rules requiring open windows and parking with exhaust downwind from the air intake.