During preparation of some reagents, that involves the use of harmful constituents like concentrated acids, students (high school students) may be prevented from entering the chemical preparation/storage area until the preparation is completed and the area is area deemed safe for students. Students may also be prevented from entering the preparation/storage area if a student does not wear the appropriate protective wear during preparation of reagents or during "trial-runs" of reagents. For example, diethyl ether has a choking smell and if a student doesn't wear a face mask, the student may be seriously affected (health-wise) by this choking substance which is hazardous when inhaled in high concentration.
For example, two different species that prey on the same or similar species of prey would be negatively effected by their competition for food, because there would be less food.