# How dangerous are drones for humans

## Drone hazard, risk and injuries

When talking about drones and the danger to be faced, there are usually two camps. Some are not in the least interested in the topic and for others, drones are a dangerous weapon that should be banned.

This specialist article analyzes the potential danger of a drone and shows solutions.

Warning: In this article, pictures of injuries caused by drones are shown at the end. If you can't see blood, don't scroll down to the end of this article! Another warning follows.

The main sources of danger of a drone are:
• Kinetic energy on serve
• propeller
• Accumulator or battery

The risks in detail:

### Kinetic energy on serve

According to the formula for the kinetic energy, the energy at the impact is:

m: model mass in kg
v: model speed in m / s
E_kin: Kinetic energy in joules

The weight is not that important compared to the speed. A model that is twice as heavy has twice the kinetic energy on impact as the original. A model that is twice as fast, on the other hand, has four times the energy compared to the original model.

### Calculation example DJI Phantom 2

With a little effort, the "DJI Phantom 2" will be able to dive around 80 km / h (approx. 22 m / s). With a weight of 1.0 kg, this corresponds to kinetic energy on impact of 247 joules.

### Calculation example hotliner

A typical hotliner (surface model, mass 1.0 kg, speed approx. 250 km / h), on the other hand, has 2411 joules on impact. This is about 10 times the energy compared to the DJI.

### Danger from impact

For comparison, the projectiles of an air gun in Germany may have a maximum of 7.5 joules, measured at the muzzle (muzzle energy).

Even if a drone releases a certain amount of energy when it crashes, the structure of the model does not allow the energy to act selectively. The structure is simply not stiff enough and will be deformed. The only exception are the engines. These are compact and stable enough to cause greater damage. It becomes much more critical when the engines turn at full power in the event of a crash.

### Danger from propellers

The danger posed by the propellers particularly concerns the following points:
• Cuts from contact with the propeller
• Cut and stab wounds from a cracked propeller
• Damage to hearing from the propellers
Since the propellers have sharp edges, cuts should not be underestimated and can cause deep wounds. If the model continues to move with the propellers running, numerous cuts will result. Even small propellers (e.g. 5 inches) can cause serious injury. Larger (8 inch and more) propellers, especially those made of CFRP, can cause very deep wounds and easily cut through the skin as well as tendons, ligaments and blood vessels. The fact that cuts from a propeller bleed profusely and leave scars should be clear to everyone.

Many pilots are not aware of the power a propeller has. Take a look at the following video and get an idea for yourself.

### Hand launch and hand landing is reckless

The pilots who recklessly start the model out of hand and catch it again are particularly at risk.

When starting or landing by hand, consider the following points:
• A mediocre model turns in less than 0.3 seconds from the horizontal starting position to the vertical and thus into the arm or face of the pilot. There is no time for the pilot to react accordingly.
• Even small models can develop amazing powers in a very short time. Even a supposedly securely held model is then no longer tenable.
• The pilot only has one hand on the remote control and can only react to a limited extent.
• A gust of wind can move the model towards the pilot.
• The model is in the immediate vicinity of sensitive body parts such as the face, neck and forearm.

### Injuries to a realistic hand made of ballistic gel

In these pictures you can see a forearm including hand and the injuries caused by a propeller. A high-quality ballistic gel was used, which is used by testing institutes and the military. The ballistic gel has the properties of human tissues such as skin and muscles. Only cuts that would lead through bones do not correspond to reality on the gel hand. There are no bones in the gel hand.

Everything still attached to the hand made of ballistic gel.

A deep cut between the thumb and forefinger through a CFRP propeller. There are no bones at this point, which is why the injury to the ballistic gel hand corresponds to reality.

Deep cuts.

The comparison with the original.

The hand stub made of ballistic gelatine.

In an emergency, the bones will offer high resistance to the propeller and thus probably prevent complete amputation of the fingers. Nevertheless, serious injuries are to be expected. In addition to severely bleeding wounds, nerves can be severed and lead to a permanent loss of sensation in individual fingers. In the face, such injuries are particularly dangerous.

### Flying propeller parts

The risk of cracked propellers has decreased significantly in recent years. This risk can be classified as low due to better manufacturing processes and the use of durable materials. However, damaged propellers should be replaced. This mainly applies to CFRP propellers that have come into contact with obstacles. The CFRP propellers can be almost undamaged on the outside, but have cracks on the inside, which completely destroy the propeller under higher loads. GRP propellers are less affected here, but, like all other propellers, should be replaced in the event of visible or suspected damage to be on the safe side. A propeller costs only a fraction of the total model. If a propeller is destroyed in a drone, the model will crash.

### Hearing damage from high-speed propellers

Hearing damage from the propellers is rare and is mainly to be expected with high-speed small propellers in reverberant environments (e.g. concrete walls). This includes, for example, flying in an underground car park close to the pilot.

### LiPo batteries as a source of danger

The battery poses a further hazard. Today's LiPo batteries have a high energy content. In connection with a fall and damage to the battery or a short circuit due to defective electronics, there is an immediate risk of fire. Pilots in particular who fly a drone through dry areas in midsummer should be aware of this danger. A burning LiPo battery must never be extinguished with water. Use a fire blanket, sand, or powder fire extinguisher instead. For practical reasons, it is advisable to take a simple fire blanket with you, especially with aggressive aerobatic models.

### Simple solution: keep your distance

Take-off and landing on the ground with a safety distance of at least 5 meters from people should be the preferred option.

The risk of injury is 1% at a distance of 5 meters if the drone flies around uncontrollably. At a distance of 10 meters it is only 0.25% (for derivation see below).

### Minimize risks when flying drones

In order to minimize the risks, general rules of common sense apply.
• Only fly a model that is OK. No “will fit” flights.
• Before starting, make sure that there are no other hazards such as obstacles.
• Fly at a safe distance from people and animals. Dogs like to chase a lower flying drone and jump high.
• Read and observe the operating manual (s)

### Fail-safe scenarios. There is only one sure thing.

A few more comments on various fail-safe scenarios. GPS is only accurate under optimal conditions. Trees, buildings, storm clouds, etc. interfere with reception. We have already tested high-quality GPS receivers that deviated from the real position by more than one kilometer when the satellite reception was poor (e.g. rain clouds). These receivers correct the position step-by-step, but in the worst case the control system has an incorrect position report. Imagine a “fly home” under such conditions. The model is going to fly somewhere with its propellers spinning. A cross-country flight with the drone is therefore dangerous.

In my opinion there is only a safe fail-safe behavior: Motors off immediately.Even if this may mean a total write-off of the model. All other scenarios such as “position hold”, “fly home” etc. are risky. Note that when such scenarios become active, there is already a problem. No radio reception means unfavorable conditions for radio transmission. This can also affect GPS reception. A model that flies around in an uncontrolled manner can cause greater damage than a model that hits the ground on a small area. As good as GPS navigation is, this technique should not be trusted blindly.

### Typical sources of error with drones

There are enough reasons for a model flying around uncontrollably.
A small selection
• Propeller incorrectly installed
• Motors rotate incorrectly
• Cable break (e.g. ESC switches off)
• Moisture on the board (rain, fog, snow)
• A transmitter mast nearby is disturbing the model
• Regulator set incorrectly
• Wiring error (e.g. motors incorrectly connected to the controller)

Other causes
• Pilot pays taxes
• Pilot is jostled
• The pilot has to sneeze
• Gust of wind
• A plug comes loose
• Remote control defective
• Pilot distracted
• ESC short circuit
• and many more

This article was written because fellow drone pilots suffered serious injuries while practicing their hobby or profession. I would like to spare you this.

### Derivation of hit probability

The following calculation is used to determine the hit probability of a model flying around in an uncontrolled manner.

Imagine the model is in the middle of a hemisphere. The pilot is right on the edge of the hemisphere. A model flying around in an uncontrolled manner will hit the ground or the hemispherical shell somewhere.

The area of ​​the circular bottom and the hemispherical shell is:

R is the radius of the circle of the ground or the hemispherical shell and corresponds to the distance to the model.

The external dimensions of the pilot are assumed to be around 180 cm x 50 cm. The quadrocopter is assumed to be punctiform so that the calculation can be carried out more easily but still precisely. For this reason, the dimensions of the pilot must be increased. It is necessary to add half the quadrocopter outer dimensions per side. In total, the dimensions of the pilot for a quadrocopter with 50 cm external dimensions (propeller tip to propeller tip) are 230 cm x 100 cm. This corresponds to 2.3 square meters.

The hit probability is the ratio of the areas to each other.

In the example calculation, the hit probability at a distance of 5 meters from the model is approx. 1%.

The following table shows some typical values ​​for the hit probability by an uncontrolled drone flying around compared to the distance to the flight model.

Warning: The following are pictures of injuries caused by drones. If you can't see blood, stop scrolling!

### Images of injuries caused by drones

Aerobatic quadrocopter: propeller incorrectly installed and manual start. Cuts just got past the nerves.

Little PFV Racer: The pilot wanted to pick up the still-armed model. When bending down, the thick winter jacket pushed the throttle forward slightly and the engines started. Two cuts down to the bone / joint. Injury to the extensor tendon of the index finger.

250 racer: When bending down and straightening the quadrocopter with clothes touching the throttle. Surface injury and injury to the nail, but luckily not deep.

This injury occurred when the drone was caught out of the air and then settled in the rear. A propeller hit the hand. Motor 2204 with 6 inch propeller.

If you have been injured by a drone yourself and have images, you are welcome to send them to me. Ideally, with a short description and approval to use the image on the website.