How Does Time on the Floor Affect Bacterial Transfer?
The 5 second rule is an urban myth stating that food dropped on the floor is safe to eat if picked up within 5 seconds. This investigation examines whether increasing contact time with the floor increases bacterial contamination, with implications for student health and public food safety practices.
Increasing the length of time food is in contact with the floor increases the number of bacteria on the food. If proven true, this widely-used "rule" poses significant health risks through exposure to pathogens like Salmonella, Campylobacter, and E. coli.
Four experiments were conducted in the school canteen using agar plates and various foods (bread, Crunchies, Lunchables). Food samples were dropped from 12.5cm height onto the floor for 5 and 30 seconds, then cultured on agar plates for one week to count bacterial colonies.
Control samples showed zero bacterial colonies. However, food exposed to the floor for 5 seconds showed bacterial growth (2-3 colonies), while 30-second exposure showed increased contamination (4-6 colonies). The floor by the table had the highest bacterial concentration (92-93 colonies).
The hypothesis is confirmed: food collects bacteria after just 5 seconds on the floor, disproving the 5 second rule. Bacterial contamination increases with longer exposure time. The 5 second rule is FALSE and poses health risks. People should avoid eating food that has contacted the floor.
Science Rules is a group of five individuals who are passionate about Science and its mysteries. We are currently working on The effects of Acid Rain. We have also done other projects such as bacteria testing as well. We hope our results will help the future experiments and explorations to come as well. We are doing this as we love Science and we think this can potentially help our careers to come.
The 5 second rule is an urban myth stating that food dropped on the floor is safe to eat if picked up within 5 seconds. This investigation examines whether increasing contact time with the floor increases bacterial contamination, with implications for student health and public food safety practices.
The 5 second rule is an urban myth stating that if food has been in contact with the floor for less than 5 seconds it is safe to eat.
Historical Origin: The rule is thought to originate from Genghis Khan, who declared that dropped food would be fine to eat until he said otherwise. Today, people commonly use this rule in their everyday lives.
School Context: Student attendance at our school is a significant concern and is decreasing. This is mostly due to illness which could result from eating food with bacteria from floor contact.
This investigation is important for a wider audience as this rule is used commonly. If proved to be false, it could be risking people's health.
• Salmonella
• Campylobacter
• Enterohaemorrhagic Escherichia coli (E. coli)
These bacteria affect millions of people annually
If Hypothesis is TRUE:
If Hypothesis is FALSE:
Increasing the length of time food is in contact with the floor increases the number of bacteria on the food. If proven true, this widely-used "rule" poses significant health risks through exposure to pathogens like Salmonella, Campylobacter, and E. coli.
Increasing the length of time food is in contact with the floor increases the number of bacteria on the food.
| Exposure Time | Expected Bacterial Count | Health Risk |
|---|---|---|
| 0 seconds (control) | Zero colonies | None - sterile food |
| 5 seconds | Measurable colonies | Moderate - bacterial transfer occurs |
| 30 seconds | Higher colony count | Higher - increased contamination |
To test this hypothesis, we must demonstrate:
| Variable Type | Description |
|---|---|
| Independent | Time in contact with floor (0, 5, 30 seconds) |
| Dependent | Number of bacterial colonies grown on agar plates |
| Controlled | Food type, drop height (12.5cm), floor location, agar plate conditions, incubation time (1 week) |
Four experiments were conducted in the school canteen using agar plates and various foods (bread, Crunchies, Lunchables). Food samples were dropped from 12.5cm height onto the floor for 5 and 30 seconds, then cultured on agar plates for one week to count bacterial colonies.
Purpose: Establish baseline bacterial levels in freshly cleaned environment
| Step | Procedure |
|---|---|
| 1 | Received agar plates from lab technician |
| 2 | Arrived at freshly cleaned canteen |
| 3 | Each team member received sterile swab |
| 4 | Assigned areas: table, chair, floor by door, floor by table |
| 5 | Swabbed assigned areas |
| 6 | Rolled swabs onto agar plates in squiggly motion |
| 7 | Sealed petri dishes with cellotape |
| 8 | Labeled dishes with location information |
Purpose: Compare bacterial levels before cleaning to determine optimal testing environment
Repeated Experiment 1 protocol before cleaners had cleaned the canteen. This experiment helped determine whether the clean or dirty canteen would provide sufficient bacterial growth for data collection.
Purpose: Test food types and methodology for conducting food contamination tests
| Step | Procedure |
|---|---|
| 1-3 | Repeated steps 1-3 from Experiment 1 |
| 4 | Dropped 1cm³ of bread and Crunchies onto floor by table from height of 12.5cm for 5 seconds |
| 5 | Placed samples on petri dishes for 5 seconds |
| 6 | Sealed petri dishes with cellotape |
| 7 | Repeated procedure for 30 seconds exposure |
| 8 | After 1 week, returned and recorded results |
Purpose: Test hypothesis on each component of Lunchables (crackers, cheese, ham)
Same method as Experiment 3 was used, testing individual Lunchables components for bacterial contamination at 5 and 30 second intervals.
| Hazard | Potential Consequence | Risk Level (1-10) | Mitigation Strategy |
|---|---|---|---|
| Bacteria growth | Bacterial growth on food | 3 | Using agar plates carefully |
| Scalpel | Cut someone | 1 | Resistant gloves or being careful |
Control samples showed zero bacterial colonies. However, food exposed to the floor for 5 seconds showed bacterial growth (2-3 colonies), while 30-second exposure showed increased contamination (4-6 colonies). The floor by the table had the highest bacterial concentration (92-93 colonies).
| Location | Number of Colonies |
|---|---|
| Floor by door | 6 |
| Indoor door | 30 |
| Seat | 53 |
| Floor by table | 93 |
| Table | 3 |
| Location | Number of Colonies |
|---|---|
| Floor by door | 6 |
| Indoor door | 29 |
| Seat | 44 |
| Floor by table | 92 |
| Table | 3 |
| Sample | Number of Colonies |
|---|---|
| Bread control | 0 |
| Bread 5 seconds | 0 |
| Bread 30 seconds | 0 |
| Crunchie control | 0 |
| Crunchie 5 seconds | 0 |
| Crunchie 30 seconds | 0 |
| Sample | Number of Colonies |
|---|---|
| Cheese control | 0 |
| Ham control | 0 |
| Cracker control | 0 |
| Cheese 5 seconds | 2 |
| Ham 5 seconds | 2 |
| Cracker 5 seconds | 3 |
| Cheese 30 seconds | 4 |
| Ham 30 seconds | 6 |
| Crackers 30 seconds | 5 |
All control samples showed ZERO bacterial colonies, confirming food was sterile before floor contact.
Bacterial growth detected: 2-3 colonies across all Lunchables components.
Increased bacterial growth: 4-6 colonies, demonstrating time-dependent contamination.
Location Selection: The canteen was chosen as the most likely place for someone to drop their food. The 'dirty canteen' was tested over the clean because it represents a realistic environment when people are more likely to drop food. Data from experiments one and two showed the dirty floor had greater bacterial concentration, providing more data.
Floor Location: The 'floor by table' location was chosen as data showed it had the greatest number of bacterial colonies (92-93), giving bacteria the best chance to grow and representing the most likely area for food to be dropped.
Control Experiments: Controls were conducted for each food to ensure there were no bacteria already present on the food before floor contact.
30 Second Testing: Extended exposure time was tested to investigate whether further bacterial growth would occur over a longer period.
Food Selection Rationale: Lunchables were chosen over Crunchies because:
The hypothesis is confirmed: food collects bacteria after just 5 seconds on the floor, disproving the 5 second rule. Bacterial contamination increases with longer exposure time. The 5 second rule is FALSE and poses health risks. People should avoid eating food that has contacted the floor.
Our research has shown that our hypothesis is TRUE: after 5 seconds, food does indeed collect bacteria from the floor, making the 5 second rule false.
• Bacterial growth detected on agar plates after 5 seconds
• Food is unsafe for human consumption after floor contact
• Contamination increases with longer exposure time
• After 30 seconds, food showed significantly more bacteria
Since bacterial growth was observed on agar plates after just 5 seconds of floor contact, the food becomes unsafe for human consumption. This disproves the popular belief that food is safe if picked up quickly.
People should be more careful when considering eating food off the floor, as it is not clean and could transmit diseases.
This information could be used to prevent food poisoning in humans due to this common misconception.
• Educate students about bacterial contamination risks
• Reassess food safety measures in schools
• Inform the public that the 5 second rule is a myth
• Promote proper food handling practices
• Discard food that has contacted floor surfaces
By educating students about the dangers of the 5 second rule, we can potentially:
This investigation opens possibilities for further research: