Legal Definitions - Hand formula

The Hand formula is a legal test used to determine whether someone's actions, or lack thereof, created an unreasonable risk of harm, thereby making them negligent. It was developed by Judge Learned Hand in a 1947 court case.

At its core, the Hand formula helps courts decide if the cost of preventing an accident was less than the potential cost of the accident itself. If it was, then failing to take precautions could be considered negligent. The formula can be expressed as: B < P * L

• B (Burden): This represents the cost or difficulty of taking adequate precautions to prevent the harm. It includes the financial expense, time, and effort required to implement safety measures.
• P (Probability): This is the likelihood or chance that the harm will occur if precautions are not taken.
• L (Loss): This refers to the gravity or severity of the potential harm if it does occur. It considers the extent of injury, damage, or other negative consequences.

According to the Hand formula, an individual or entity is considered negligent if the burden (B) of taking precautions is less than the probable gravity of the harm (L) multiplied by the probability that the harm will occur (P). In simpler terms, if it would have been relatively easy and inexpensive to prevent a potentially serious and likely accident, and those precautions were not taken, then negligence may be found.

Here are some examples illustrating the Hand formula:

• Example 1: A Restaurant's Wet Floor

  Imagine a busy restaurant where a server spills a drink in a high-traffic area. The manager decides not to immediately place a "wet floor" sign or have an employee stand by the spill while waiting for cleanup, thinking it's too disruptive to customers. Shortly after, a patron slips on the spill, falls, and breaks their wrist.

  • B (Burden): The burden of placing a "wet floor" sign or having an employee temporarily guard the spill is very low. It involves minimal cost (a sign) and negligible disruption.
  • P (Probability): The probability of someone slipping on a wet floor in a high-traffic restaurant is relatively high.
  • L (Loss): The potential loss from a slip and fall can be significant, ranging from minor bruises to severe injuries like a broken wrist, requiring medical treatment and lost wages.

  In this scenario, B (low burden of precaution) is likely much less than P * L (high probability of significant harm). Therefore, a court applying the Hand formula would likely find the restaurant negligent for failing to take reasonable precautions.

• Example 2: A Construction Site's Safety Netting

  A construction company is building a high-rise apartment building. Industry standards recommend installing safety netting around the perimeter of each floor as construction progresses to catch falling debris or tools. The company decides to skip this step on a few floors to save time and money, believing the risk of falling objects is low if workers are careful. A worker accidentally drops a heavy tool from an unprotected floor, injuring a pedestrian below.

  • B (Burden): The burden of installing safety netting involves some cost for materials and labor, and it might slightly slow down the construction process.
  • P (Probability): Even with careful workers, the probability of tools or debris accidentally falling from a high-rise construction site is not negligible.
  • L (Loss): The potential loss from a heavy object falling from a significant height onto a pedestrian is extremely high, potentially causing severe injury, permanent disability, or even death.

  Here, even if the burden (B) of installing netting is moderate, the very high potential for severe loss (L) multiplied by a non-negligible probability (P) would likely make P * L much greater than B. The Hand formula would suggest the construction company was negligent for not installing the safety netting.