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Worksheet Grade 12 Health & Consumer Science

Lifeguard Shift at Ravensby Pool: Chloramines and Swimmer Illness

A grade 12 health worksheet for new lifeguards: read a fictional indoor pool log, find combined chlorine, and choose the actions that prevent swimmer illness.

Objectives

  1. Students will explain the difference between free and combined chlorine and why chloramines cause eye and breathing irritation at indoor pools.
  2. Students will calculate combined chlorine from a pool log and compare the log with an operating policy.
  3. Students will describe the lifeguard actions and swimmer habits that prevent recreational water illness, including the response to a diarrhea incident.

Vocabulary

pH
pH is a number that tells whether water is acidic, like lemon juice, or basic, like baking soda mixed in water. Pure water sits in the middle of the scale at a pH of 7.

Also: free chlorine, combined chlorine, chloramines, hypochlorous acid, recreational water illness, Cryptosporidium, hyperchlorination

Teacher overview

High school seniors who earn lifeguard certification often take their first paid jobs at community pools, where they are expected to notice water problems and report them. This worksheet places students on a Saturday shift at the Ravensby Aquatic Center, a fictional indoor pool, with the day's chemical log and a short excerpt from the center's fictional operating policy. Students calculate combined chlorine, compare the log with the policy, and decide what to report and what to do when a toddler has a diarrhea accident in the water.

The misconception at the center of the worksheet is that a strong "chlorine smell" means a pool has too much chlorine. The smell, and the red eyes and coughing that often come with it, usually signal chloramines, which form when chlorine reacts with sweat, urine, and body oils. A pool with a heavy smell often needs more free chlorine and better ventilation, along with swimmers who shower first. A second misconception is that chlorinated pool water kills every germ quickly. Cryptosporidium can survive in a well-kept pool for a long time, which is why diarrhea incidents call for special steps and why people with diarrhea should stay out of the water.

Lifeguard Shift at Ravensby Pool: Chloramines and Swimmer Illness — Grade 12 Health & Consumer Science
Name: ____________________________ Date: ______________

Student Worksheet

Your shift. You are a newly certified lifeguard at the Ravensby Aquatic Center, a fictional indoor pool. Before each shift, lifeguards read the chemical log that the pool operator keeps.

Background. Free chlorine is the form of chlorine that kills germs. When chlorine reacts with sweat, urine, and body oils that swimmers bring into the water, it forms chloramines. Chloramines are measured together as combined chlorine. Combined chlorine equals total chlorine minus free chlorine. Chloramines are poor germ killers. They cause the strong smell most people think of as "chlorine," and they can make eyes red and cause coughing or wheezing, especially at indoor pools where they build up in the air. Chlorine also works less well at a higher pH, because more of its strongest germ-killing form, hypochlorous acid, changes into a much weaker form called hypochlorite ion. Cryptosporidium, a parasite that causes diarrhea, can survive in properly chlorinated pool water for a long time. Showering before swimming, taking bathroom breaks, and staying out of the pool when sick with diarrhea all reduce these problems.

Excerpt from the fictional Ravensby operating policy:

  • Free chlorine must stay between 2.0 and 4.0 mg/L.
  • Combined chlorine must stay at or below 0.4 mg/L.
  • pH must stay between 7.2 and 7.8.
  • If any reading is outside its range, the lifeguard on duty tells the pool operator right away and writes the time in the log.
  • If a swimmer has a diarrhea accident in the pool, the lifeguard clears everyone from the water at once, notifies the supervisor, and keeps the pool closed until the operator completes the health department's disinfection steps, which use higher chlorine for a set time.

Saturday chemical log (fictional):

Time Free chlorine (mg/L) Total chlorine (mg/L) pH Swimmers in the pool
7:00 a.m. 3.0 3.2 7.4 0
10:00 a.m. 2.6 3.1 7.5 45
1:00 p.m. 2.1 2.9 7.7 80
4:00 p.m. 1.6 2.5 7.9 60
  1. In your own words, explain the difference between free chlorine and combined chlorine.
  2. A swimmer says, "The pool smells so strongly of chlorine that it must be extra clean today." Using the background, explain what the smell actually indicates.
  3. Calculate the combined chlorine at 10:00 a.m.
  4. Calculate the combined chlorine at 1:00 p.m.
  5. Calculate the combined chlorine at 4:00 p.m.
  6. At which log time did combined chlorine first go above the policy limit of 0.4 mg/L?
  7. At 4:00 p.m., free chlorine was 1.6 mg/L. By how much was it below the policy minimum of 2.0 mg/L?
  8. The pH rose from 7.4 at 7:00 a.m. to 7.9 at 4:00 p.m. Using the background, explain why the higher pH made the pool's chlorine less effective at killing germs.
  9. Compare the swimmer counts with the combined chlorine readings you calculated. Describe the pattern and explain what causes it.
  10. At 2:30 p.m., a parent tells you that her toddler just had a diarrhea accident in the pool. According to the policy, what must you do first?
  11. Using the background, explain why a diarrhea accident calls for more than the pool's normal chlorine level.
  12. Write two rules for a sign at the pool entrance that would reduce both chloramines and the spread of illness, and explain how each rule helps.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: Free chlorine is the form that kills germs, while combined chlorine is chlorine that has already reacted with sweat, urine, and body oils to form chloramines, which are poor germ killers.
    Accept any answer that names free chlorine as the active disinfectant and combined chlorine as chlorine tied up in chloramines.
  2. Answer: The strong smell usually comes from chloramines, which means chlorine has been used up by sweat, urine, and body oils, not that the pool is extra clean.
    Strong answers add that the same chloramines cause red eyes and coughing, especially indoors.
  3. Answer: 0.5 mg/L.
    Total chlorine minus free chlorine: 3.1 minus 2.6 equals 0.5 mg/L. Check: 2.6 plus 0.5 equals 3.1.
  4. Answer: 0.8 mg/L.
    2.9 minus 2.1 equals 0.8 mg/L. Check: 2.1 plus 0.8 equals 2.9.
  5. Answer: 0.9 mg/L.
    2.5 minus 1.6 equals 0.9 mg/L. Check: 1.6 plus 0.9 equals 2.5.
  6. Answer: The 10:00 a.m. reading.
    At 7:00 a.m. combined chlorine was 3.2 minus 3.0, or 0.2 mg/L, which meets the policy. At 10:00 a.m. it was 0.5 mg/L, which is above the 0.4 mg/L limit. Under the policy, the lifeguard should have told the operator at that time.
  7. Answer: 0.4 mg/L.
    2.0 minus 1.6 equals 0.4 mg/L below the minimum. Check: 1.6 plus 0.4 equals 2.0.
  8. Answer: At a higher pH, more of the hypochlorous acid changes into the weaker hypochlorite ion, so the same amount of free chlorine kills germs more slowly.
    Accept answers that describe the shift to a weaker form without naming both chemicals. The 7.9 reading at 4:00 p.m. was also above the policy's upper limit of 7.8, so it should have been reported.
  9. Answer: Combined chlorine rose through the day as more swimmers used the pool, because swimmers add sweat, urine, and body oils that react with chlorine to form chloramines.
    The log shows no swimmers and 0.2 mg/L at 7:00 a.m., then 45 swimmers and 0.5 mg/L, then 80 swimmers and 0.8 mg/L. Strong answers note that combined chlorine kept rising at 4:00 p.m. with fewer swimmers, because chloramines that have already formed stay in the water until they are removed.
  10. Answer: Clear everyone from the pool at once and notify the supervisor.
    The pool stays closed until the operator completes the health department's disinfection steps. Accept answers that include recording the time in the log as well.
  11. Answer: Cryptosporidium can survive in normally chlorinated pool water for a long time, so the pool needs higher chlorine for a set time before swimmers return.
    Accept answers that explain the parasite's resistance to normal chlorine levels.
  12. Answer: Accept any two sound rules with explanations, such as "Shower before you swim," "Take bathroom breaks every hour," "Do not swim if you have had diarrhea," or "Change diapers in the changing room, not at the poolside."
    Showering and bathroom breaks keep sweat and urine out of the water, which reduces chloramines. Staying out when sick with diarrhea and changing diapers away from the pool reduce the chance that germs such as Cryptosporidium get into the water.

Differentiation

Support

Add a blank "combined chlorine" column to the log and work the 7:00 a.m. row together as a class before students complete items 3 through 5. Give students a one-line summary card of the policy ranges, with each range drawn as a short number line so they can see at a glance whether a reading falls inside it.

Extension

Ask students to draft the incident report a lifeguard would file for the 2:30 p.m. event, including the time, the actions taken, and who was notified, and then to write a short note to the pool manager recommending two changes, such as ventilation or a pre-swim shower check, that would lower chloramines on busy Saturdays at the fictional center.

ELL supports

Pre-teach "free," "combined," "total," "diarrhea," "ventilation," and "policy" with simple definitions and a picture of a pool with arrows showing sweat and urine meeting chlorine. Provide the frames "Combined chlorine is ___ minus ___." and "A lifeguard should ___ because ___." Allow students to answer item 12 with a drawn sign that includes one short sentence per rule.

Extensions

If a local pool is willing, invite a certified pool operator to describe how the facility tests its water, how often it records readings, and what it does after a fecal incident. Students can compare the real procedure with the fictional Ravensby policy and list one difference.