Miller Gardner, the 14-year-old son of the retired Yankees player Brett Gardner, died from carbon monoxide poisoning while on vacation in Costa Rica. Here’s why the gas is so dangerous.

Carbon monoxide, often called the “silent killer,” has no taste, odor or color, yet prolonged inhalation of the invisible gas is suspected in the recent deaths of several American tourists traveling abroad.

When carboxyhemoglobin saturation exceeds 50%, it is considered lethal. In Gardner’s case, the test showed a saturation of 64%.