Columns > Published on April 4th, 2018

Writing the Crime Scene: Blood

A rookie cop nurses a busted nose after a dust-up with a drunken thug. The veteran detective squats down to examine crimson stains on the kitchen floor. A forensic specialist tests a blood-stained jacket for the suspect's DNA. Blood is a common element in every crime or horror novel. Each of our characters has roughly one to one-and-a-half gallons of blood in their fictional veins. So when you see horror movies where there is a firehose of scarlet shooting out of a severed limb, it isn’t really accurate. To maintain your authority as a writer, you need to get the details correct. This article will help clear up some common misconceptions about blood and help you write about it more effectively.

It’s Only A Flesh Wound

We’ve all seen horror films where massive amounts of fake blood spray from a wound. But how much blood will actually spurt from a real severed artery? And how far will it spray? There are nearly two dozen major arteries in the human body, the most commonly-known being the carotid (head and neck), femoral (lower extremity), subclavian (upper extremities) and the aorta. If a character’s carotid artery—found on either side of the neck and responsible for supplying blood to the brain—is completely severed, it will gush blood, but the spray will not go very far due to the total loss of pressure. However, if an artery is only nicked rather than slashed wide-open, it will squirt much further given the increased pressure and for a longer period of time. Think of it like a garden hose with your thumb over the end.

To maintain your authority as a writer, you need to get the details correct.

A murder case covered in Time magazine in 1933 featured testimony from an expert who determined that a severed artery could spray 6 inches vertically and 18 inches laterally. I'm not suggesting you get specific and technical about your distances. Just use common sense and keep your gushing wounds from seeming over-the-top and ridiculous. Also remember that once the heart stops, the blood stops flowing and there is no blood pressure in the body. Post-mortem wounds don't bleed as they normally would. There will likely be 'liberated fluids,' but any movement of blood would be based solely on gravity.

It's About Bloody Time

How long will your character survive with a bleeding wound? If blood loss isn't slowed through medical attention, it really depends on the area of the body and the severity of the wound. A nosebleed isn't likely to kill your protagonist anytime soon, but a cut to the femoral artery (located in the upper leg) will cause unconsciousness in roughly sixty seconds and death in less than five minutes. Don't forget to get inside your character and describe their mental state and the physiological effects of blood loss. Early symptoms of hemorrhaging include headache, fatigue, nausea and dizziness. Without treatment, the character will soon experience rapid heart rate, shallow breathing, and pale, clammy skin. Their thoughts will become more muddled and confused as shock sets in and the situation gets worse.

How much blood can your character lose before they die? To put it in perspective, when you donate blood at a clinic, you’re giving them about 10% of your body’s supply. At 15-30% of blood loss, the character’s heartbeat will increase rapidly as their blood pressure plummets. They’ll look pale and their skin will become cool. Light-headedness and loss of mental clarity will begin at this phase. Once blood loss levels reach 30-40%, shock will set in and the character's mental state will really start to plummet. That's about 3-4 pints for the average person. At this point, they're in real trouble without an immediate stoppage of the flow and an external blood source to provide a transfusion. 

Coagulation Makes It Happen

I recently read a manuscript where a police officer slipped in a puddle of blood spilled from a day-old corpse. Not so sure about that. Blood will coagulate in roughly eight to fifteen minutes after leaving the human body. Take care to think thorough your scenes to make sure you're not making an obvious gaff. There simply isn't enough space here for me to cover all the aspects of blood in fiction. For more information about blood testing for DNA, forensic spatter analysis and general information about how blood works in our bodies, check out chapter 9 of my go-to layman's book on forensics for crime writers, below.

About the author

Repo Kempt has worked as a criminal lawyer in the Canadian Arctic for over ten years. He is the author of a book about seal hunting, a member of the Horror Writers Association, and a guest columnist for the Canadian Broadcasting Corporation. He lives on a cricket farm with his wife, Joy and his little dog, Galactus. In his spare time, he looks for an agent for his latest manuscript.

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