Blood is extremely dangerous when carried to the blood via the lungs by inhalation, because carbon monoxide irreversibly binds to hemoglobin to form carboxyhemoglobin, so that less hemoglobin is free to bind oxygen, and fewer oxygen molecules can be transported throughout the blood. This can cause suffocation insidiously. A fire burning in an enclosed room with poor ventilation presents a very dangerous hazard, since it can create a build-up of carbon monoxide in the air. Some carbon monoxide binds to hemoglobin when smoking tobacco. Blood for transfusion is obtained from human donors by blood donation and stored in a blood bank.
Hemoglobin Hopkins-2 carboxyl group of the amino acid forms a hydrogen bond with phenolix hydroxyl, which in turn stabilizes the structure of the molecule and increases oxygen affinity. Ho-2 hemoglobin has high levels of oxygen, which replaces the lack of oxygen within red blood cells. Ho-2 is similar to Hemoglobin A, which is normal hemoglobin and also contains two α-chains. This provides an explanation as to how the Hopkins-2 variant of hemoglobin is related to the symptoms of sickle cell. Hopkins-2 can also interact specifically with Hemoglobin S. Hemoglobin S is the most common abnormal hemoglobin variant. Hemoglobin S is the variant