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Communicable Diseases Module: 10. Malaria Prevention: Indoor Residual Spraying of Houses

Study Session 10  Malaria Prevention: Indoor Residual Spraying of Houses

Introduction

In this study session, you will learn about one of the most important and widely used methods to control adult mosquitoes in Ethiopia: indoor residual spraying (IRS) of houses. IRS involves spraying the inside of houses with insecticides (chemicals that kill insects). The insecticides used in IRS are long-lasting and kill the vector when it enters houses to bite people.

Your role will be critical in the success of IRS in your community, so it is important for you to understand the objectives, techniques and challenges of undertaking IRS campaigns. We will explain how IRS helps to prevent malaria, and how to plan and carry it out. You will also learn about the safe handling of insecticides, the selection and training of spray operators, and the operation of spray pumps.

To undertake IRS effectively in your village, you will need training in several practical skills, such as spray techniques, training of spray operators, maintenance of spray pumps, etc. The additional practical training will be arranged by your Regional Health Bureau.

Learning Outcomes for Study Session 10

When you have studied this session, you should be able to:

10.1  Define and use correctly all of the key words printed in bold. (SAQ 10.1)

10.2  Explain how IRS works to kill malaria vectors and protect people from malaria. (SAQs 10.1 and 10.2)

10.3  Explain the logistic requirements to undertake IRS effectively, using standard IRS techniques. (SAQs 10.3, 10.4, 10.5 and 10.6)

10.4  Calculate the IRS coverage in a village. (SAQs 10.5 and 10.6)

10.5  Describe how to safely handle and dispose of insecticides. (SAQ 10.7)

10.1  Introduction to indoor residual spraying (IRS)

In Study Session 9 you learned that environmental management and other larva killing activities are important in malaria prevention. Larval control is the first line of defense in malaria prevention; its impact in reducing the burden of malaria can be significant in countries like Ethiopia, where vector breeding sites are relatively limited and generally clearly defined. However, it is impossible to identify all vector breeding sites and kill all larvae before they become flying adults. Once mosquitoes become flying adults, environmental management has little impact in controlling them, so measures to control adult mosquitoes are needed to protect people from malaria.

Indoor residual spraying (IRS) has been used in Ethiopia since the 1960s, and has three main aims:

  1. To reduce the seasonal rise in malaria.
  2. To prevent epidemics.
  3. To control epidemics.

Until 2009, IRS was planned and implemented by specialised staff from district, zonal and regional health offices. Temporary spray operators were recruited from district towns and sent to villages to do the spraying.

However IRS will now be planned and implemented by Health Extension Workers and Health Extension Practitioners like yourself in your own village, with the co-operation of your local community. As part of this process, you will need to train spray operators (the people who do the spraying) selected from the community, supervise the spray operation, and carry out minor maintenance of the spray pumps (equipment used to spray insecticides).

10.2  How does IRS reduce the mosquito population?

In Study Session 5, you learned that mosquitoes enter houses to take blood from humans, mainly at night. Mosquitoes do not fly for long after feeding, as the blood meal they take is more than twice their unfed body weight and they need to spend some time resting. Following a blood meal, the female mosquitoes tend to rest in undisturbed sites for two to three days until their eggs develop and are ready for laying. (Remember that the males do not take blood meals and so are not vectors of malaria.) Understanding the resting habits (the preferred resting places and behaviour) of the malaria vectors is extremely important for IRS programmes.

In drier regions, rooms inside houses are important resting places for mosquitoes because they prefer humid environments and it is usually more humid indoors. In humid forested areas mosquitoes may also rest in vegetation outdoors. However, even species that normally rest outdoors enter houses to feed and will spend some time resting indoors after feeding.

If the inside of a house has been sprayed with insecticide, when mosquitoes rest in the house they come into contact with the residual (long-lasting) insecticide sprayed on walls and furniture, and they die within a few hours.

Parasite development inside a female mosquito takes about 10 days and mosquitoes feed and lay their eggs every two to three days. So they may have to bite people three to four times before the parasite develops fully and they are able to transmit the infection. Every time a mosquito visits a sprayed house to feed on people, it is at risk of coming into contact with the insecticide and dying.

Mosquitoes resting on sprayed walls come into contact with insecticide through their feet and are killed. Some insecticides also irritate mosquitoes and cause them to leave houses before biting. In dry or windy areas, this may also result in death due to lack of suitable outdoor resting places.

Wall-spraying may not prevent biting. Hungry mosquitoes entering a house often bite first and then rest on walls and furniture inside houses. As most anopheline vectors of malaria enter houses to bite and rest, malaria control programmes have focused primarily on the indoor application of residual insecticides to the walls and ceilings of houses.

Indoor residual spraying is one of the primary vector control interventions for reducing and interrupting malaria transmission and one of the most effective methods. The primary effects of IRS towards reducing malaria transmission are:

  1. It reduces the life span of vector mosquitoes, so that they cannot live long enough to transmit malaria parasites from one person to another.
  2. It reduces the density/number of the vector mosquitoes.
  3. Some insecticides used in IRS also repel mosquitoes and by so doing reduce the number of mosquitoes entering the sprayed houses and thus reduce human-vector contact.

However, note that IRS may not provide individual protection – people sleeping in sprayed houses may still be bitten by mosquitoes. Unlike insecticide treated nets (ITNs are the subject of Study Session 11), which provide individual protection from mosquitoes, the aim of IRS is to provide community protection.

10.3  The IRS programme in Ethiopia

The insecticide called DDT has been used for IRS in Ethiopia since the mid-1960s. However, there is now widespread resistance of malaria vectors to DDT, so it will not be used in Ethiopia for IRS after 2010. Decisions about which insecticide to spray are made at the national level. When to spray is also often decided by malaria experts at the district or regional level, but you may also have a valuable input because you have better knowledge of the malaria transmission pattern in your village.

Areas less than 2,000 metres above sea level are generally considered malarious in Ethiopia, although there are marked variations between places and seasons. As a result, most of the areas below 2,000 metres are considered IRS targeted areas. The decision on whether your village will be sprayed or not is made at the district level. Depending on the local pattern of malaria cases, the availability of resources and the forecast of the risk of malaria, your village may be sprayed once a year, twice a year, during some years but not others, or not sprayed at all.

IRS has to be done during the rainy season and be completed just before the rain stops.

10.4  Spraying requirements

Before spraying is undertaken, detailed information has to be collected on the number of households in the village, the number of unit structures (houses/rooms) in each household, the average surface area of every house in the village, and the season of malaria transmission. Effective insecticide spraying also requires trained personnel. In your case, the spray operators will be community members selected and recruited by you in consultation with your supervisor at the health centre. The spray operators will carry out spraying duties seasonally. Spraying equipment needs maintenance, and spare parts must be available. Box 10.1 lists the supplies and equipment used for IRS.

Box 10.1  Supplies and equipment used for IRS

  • Spray pumps (Figure 10.1) of eight litre capacity
  • Insecticides
  • Spray pump spare kits
  • Tool kits for pump maintenance
  • Personal protective equipment (you will see a drawing of a spray operator wearing this equipment later, in Figure 10.6):
    • coverall,
    • waterproof hats or helmets,
    • face shields or goggles,
    • respiratory masks,
    • gloves,
    • rubber boots.
A labelled diagram of the parts of a spray pump for IRS.
Figure 10.1  Parts of a spray pump for IRS. (WHO, 1997; source as in Figure 9.2)

All these supplies and equipment will be provided to your health post by the District Health Office. They will make sure that you have everything you need before starting to train spray operators and beginning the spraying programme.

10.5  Insecticides for IRS

10.5.1  Choice of insecticides

Insecticide(s) for IRS are selected based on evidence of effectiveness and should have the following properties. They must:

  • Kill more than 90% of the mosquitoes that make contact. Note, however, that mosquitoes can develop resistance to the insecticide used in IRS. If people in your community experience a high number of mosquito bites even if their houses are sprayed, or there are many mosquitoes resting inside sprayed houses, these could be early signs of resistance and should be reported to your supervisor.
  • Remain effective at killing mosquitoes for a long time – that is, they must be long-lasting.
  • Be safe for humans and domestic animals.
  • Be acceptable to the community.

10.5.2  Commonly used insecticides

Residual insecticides for IRS are generally in the form of powders or liquids. Water-dispersible powder consists of a powdered insecticide mixed with a substance that allows the insecticide to dissolve in water. For indoor spraying purposes, the water-dispersible powder is the most effective form. Any of the insecticides shown in Table 10.1 can be used for IRS in Ethiopia for the coming several years. Most insecticides come in pre-weighed sachets; one sachet is to be used per one spray pump of eight litre capacity.

Table 10.1  Insecticides used for IRS in Ethiopia.
Name of insecticideChemical typeDosage (in grams per square metre)
MalathionOrganophosphorus2 g/m2
FenitrothionOrganophosphorus1 or 2 g/m2
PropoxurCarbamets1 or 2 g/m2
BendiocarbCarbamets0.2–0.4 g/m2
DeltamethrinSynthetic pyrethroids0.025–0.05 g/m2
PermethrinSynthetic pyrethroids0.5 g/m2
LambdacyhalothrinSynthetic pyrethroids0.025–0.05 g/m2
CypermethrinSynthetic pyrethroids0.5 g/m2

10.6  Determining insecticide requirements

The amount of insecticide required for your village depends on:

  • The type of insecticide to be sprayed.
  • The number of households and housing units (a structure/room used by households for sleeping, storage, shelter for animals or other purposes) in your village.
  • The average surface area of the housing units; surface area refers to the area of the walls, roof and furniture to be sprayed by insecticide; if houses are big in your village, they will have more surface area to be sprayed and need more insecticide per house than will be needed to spray small houses.

The type of insecticide to be sprayed is decided nationally. Information about the number of households and housing units for your village is kept at the District Health Office (and may need to be updated by you from time to time). The average surface area of the housing units in your village is also known by the District Health Office. If necessary you can work with experts from the District or the Regional Health Office to update these measurements. Based on the above data, the amount of insecticide required for IRS in your village is calculated by experts at the District Health Office and sent to you at your health post.

You are responsible for the safe storage and handling of the insecticide at the village level. Most insecticides are pre-weighed and pre-packed in sachets that have to be dissolved in 8 litres (8,000 ml) of water to fill a spray pump. 40 ml of the insecticide needs to be sprayed per square metre (m2) of surface area, so a full spray pump (8,000 ml) is enough to spray 200 m2.

10.7  Housing units and structures to be sprayed with insecticide

You need to know which areas and items in a household to spray during IRS.

All potential resting places for mosquitoes need to be sprayed. Resting places are all walls and ceilings in the house, window frames, and both sides of doors, furniture (beds, tables and chairs), animal shelters, latrines, stores and outhouses.

  • Why are the outer walls and roofs not sprayed?

  • These surfaces are not generally used by mosquitoes for resting.

To ensure that IRS provides good protection against malaria vectors, you should aim to spray 100% of the housing units and other structures in your village.

Less than 85% coverage with IRS is not sufficient to provide adequate protection to your community, so it would be a waste of time and resources.

10.8  Training of spray operators

The outcome of IRS is highly dependent on the quality of training given to spray operators. This training will be your responsibility.

You will get a national manual with detailed instructions on the training of spray operators.

The training should address spray techniques, environmental and human safety issues, as well as communication of key IRS messages (explained in Section 10.11). The spray operators should be trained to cover 19 m2 at a constant rate within one minute. This will allow the application of 40 ml of insecticide suspension per 1 m2 of sprayable surface; 1 litre of suspension covers 25 m2 when the nozzle tip is effectively kept at 45 cm distance from the spray surface.

The wall of a building can be used for practice. Mark an area 3 m high and 6.35 m long, divided into nine bands: the first band should be 75 cm wide and the remainder 70 cm wide (Figure 10.2). The spray nozzle will produce a swathe of spray 75 cm wide if kept at a distance of 45 cm from the wall (Figure 10.3).

Training board for residual spraying which can be marked with chalk on the wall of a large building.
Figure 10.2  Training board for residual spraying which can be marked with chalk on the wall of a large building. (WHO, 1997; source as in Figure 9.2)
The spray nozzle discharge pattern.
Figure 10.3  The spray nozzle discharge pattern is 75 cm wide when the nozzle is held at 45 cm from the sprayed surface. (WHO, 1997; source as in Figure 9.2)

10.9  Timing of spray operation

In areas where malaria transmission is seasonal, IRS should be completed just before the season begins. Generally, only one round of spraying is done per year in Ethiopia. In areas where the main transmission season is from September to late November, spraying must be completed in August at the latest. For areas with a different malaria transmission pattern, the timing of spraying should be adjusted in consultation with malaria experts at the District Health Office.

10.10  Preparation of houses before spraying

Houses need to be prepared for spraying, so householders should be informed in advance of the date and time of spraying. This should help to increase IRS coverage in the community and could be done through the village administration and other community organisations.

To prepare a house for spraying, all food, cooking utensils, bedding and clothes must be protected from the insecticide by taking them outside the house before spraying starts. Alternatively they should be placed in the centre of a room and covered with a plastic sheet to stop the insecticide settling on them.

All portable furniture should be moved away from the walls so that the walls and all sides of all the pieces of furniture can be sprayed.

10.11  Undertaking IRS operations

You will learn IRS techniques from your local mentor during practical training. You will also receive detailed instructions via the national IRS guidelines from the Federal Ministry of Health. In this section, only the most important aspects of IRS technique will be described.

10.11.1  Correct IRS procedures

  • Make sure that the house is ready for spraying (as explained in Section 10.10).
  • The outside of the front door is the first surface to be sprayed.
  • After entering the house, close the front door and spray it on the inside, including all frames of the door.
  • Start the next swathe of spraying from the bottom corner of the wall to the right of the front door and proceed clockwise as shown in Figure 10.4. Spray all edges and corners of windows, as well as all niches and cracks where mosquitoes might rest.
  • The backs, undersides and interiors of all cupboards, boxes, ovens, calendars, pictures, stools, beds, chairs and tables must be sprayed.
  • Other household areas, i.e., kitchen, store, stable and latrine, should be sprayed next.
Correct indoor spraying procedure.
Figure 10.4  Correct indoor spraying procedure. (WHO, 1997; source as in Figure 9.2)
  • After spraying, a final inspection is made by the spray operator to see that no surfaces on which mosquitoes might find a sheltered resting place remain unsprayed.
  • Following inspection by you, the spray operator is assigned to another house.
  • After spraying, the spray operator must tell each householder:
    • Not to enter the house for 30 minutes.
    • Not to re-plaster, mud-wash or white-wash inside the house for six months.
    • The spraying is to control malaria vector species, not bed bugs, fleas, etc.
    • To clean the floor and bury or burn the dirt, which is contaminated with insecticide.

10.11.2  What you need to do to support IRS

It is your responsibility as the local member of the Health Extension Service, to carry out the following duties during an IRS operation:

  • Inspect all spray pumps daily to make sure they are in perfect working condition.
  • Ensure spray operators have enough insecticide sachets for the job, and are carrying all the necessary spraying equipment.
  • Carry enough spraying record forms (Table 10.2) for the number of households to be sprayed each day.
  • Supervise the work of each of the spray operators to ensure the correct procedures are being followed.
  • After spraying is finished, inspect the house for the quality of spraying and complete the spraying record form (Table 10.2) for all households sprayed or unsprayed
  • Complete the village spraying report using the form indicated in Table 10.3.
  • Make every effort not to leave any houses unsprayed. Householders who refuse to have their houses sprayed have to be convinced by means of proper health education during the operation. Locked houses left unsprayed during the initial visit have to be revisited before the end of the day’s work or the next day.
Table 10.2  Household spraying record.
Region _________ Zone _________District _________Village _________Spray Period _________
Household No.Name of head of household or familyNo. of people in the familySprayed housing unitsNot sprayed housing unitsSpray operator numberRemark
Total
Table 10.3  Village spraying report by a Health Extension Practitioner
Region _________ Zone _________District _________Village _________Spray Period _________
Name of sub-villageHouseholdsHousing unitsPopulation protected No. of insecticide sachets usedRemark
TotalSprayedNot sprayedTotalSprayedNot sprayedNo. of people in sprayed housing unitsNo. of people in unsprayed housing units
Total

10.12  The role of the health post, health centre and District Health Office in IRS operations

Now that IRS will be decentralised to the health post level, the responsibility of planning, and organising a spray operation is shared between the District Health Office, the Health Extension Supervisor (at the health centre) and you, the Health Extension Worker or Practitioner (at the health post).

Decentralisation of the IRS operation has several advantages compared to the previous method of planning and undertaking it from the district. For example:

  • The operation could be more quickly organised at community level and implemented to control epidemics.
  • The spraying is undertaken by you, an important and familiar person in the community, and trusted spray operators selected from the community; this will increase acceptability of the operation.
  • Pumps will now be available at the health post and can be used for other malaria control purposes, such as larviciding whenever necessary.

Your responsibility in IRS operations in the village will be to:

  1. Select capable spray operators from the community.
  2. Train the spray operators for 5–7 days; (spray techniques, communication, safe handling of chemicals, etc).
  3. Plan when to start and finish the IRS operation in your village; consult also the village leaders.
  4. Undertake the IRS operation as the leading person guiding and supervising the spray operators.
  5. Mobilise the community to cooperate and participate.
  6. Educate the people about the benefits of IRS and what to do after their houses are sprayed.
  7. Keep records of your daily output and usage of insecticides.

The operation you undertake in your village will be supervised by the Health Extension Supervisor at the health centre and experts from the District Health Office. They will provide you with any technical support and equipment that you need (spray pumps, insecticides, spray pump spare kits, tool kits for pump maintenance, personal protective equipment), and answer any questions you might have.

10.13  Safe handling of insecticides

All insecticides are poisonous and must be handled with care. The following precautions are recommended and should always be practiced:

  • Anyone handling insecticides should be informed of the risks involved in their use, and should receive instructions for handling them safely.
  • You should adequately supervise spray operators to ensure they are following instructions.
  • The spray operator must wear a hat and clothing that covers as much of the body as possible, including arms and legs; the nose and mouth should be covered with a disposable or washable mask (Figure 10.5).
A spray operator in personal protective equipment.
Figure 10.5  Personal protective equipment for spray operators engaged in IRS. (WHO, 1997; source as in Figure 9.2)
  • Hands and faces should be washed with soap and water after spraying and before eating, smoking or drinking.
  • Insecticide spray should not fall onto arms, legs or other parts of the body. If the insecticide gets on to skin, it should be washed off immediately with soap and water.
  • Leaky spray equipment should be repaired.
  • Operators should bathe at the end of every day’s work and change into clean clothes
  • Clothes should be changed immediately if they become contaminated with insecticides.
  • Operators should inform you immediately if they do not feel well.
  • At the end of the day's work, washings from the sprayer should be put into pit latrines, if available, or into pits dug especially for this purpose and away from sources of drinking water.
  • Any leftover insecticide must not be poured into rivers, pools or drinking water sources.
  • Empty insecticide containers should not be re-used.

10.14  Some problems related to house-spraying

  1. In some areas mosquitoes may become resistant to commonly used insecticides. If resistance develops, insecticides are changed by the national experts.
  2. Spraying walls often leaves a visible deposit of insecticide, especially when a wettable powder suspension is used. To prevent objections to spraying on these grounds, you should educate householders on the benefits of IRS.
  3. Some people may object to wall-spraying on religious grounds; the education and communication you offer is important.
  4. The washing or re-plastering of walls, for religious or cultural reasons, reduces or eliminates the killing-power of insecticides; households should know that re-plastering during the malaria season is bad for their health.
  5. The community may be reluctant to allow strangers into their houses, for fear that they will interfere with women or steal; this will not be a problem if spray operators are recruited from the community.
  6. The insecticides may not kill other domestic pests, such as bedbugs; acceptability increases when the insecticides also kill other pests, but households should know that the objective of IRS is to kill mosquitoes and prevent malaria.

Summary of Study Session 10

In Study Session 10, you have learned that:

  1. IRS is one of the most important vector control and malaria prevention methods widely used in Ethiopia.
  2. Insecticides are sprayed onto the inner walls of houses, furniture and other structures using hand-operated spray pumps.
  3. The main objective of IRS is to kill adult mosquitoes that enter houses to bite people and rest inside houses after a blood meal.
  4. IRS may not provide individual protection; people sleeping in sprayed houses can still be bitten by mosquitoes.
  5. Unlike ITNs which provide individual protection, the aim of IRS is to provide community protection. All structures that could be used as resting places should be carefully sprayed to deny any safe shelter for the vector mosquito; achieving high coverage is extremely important.
  6. It very important that instructions on safe handling and disposal of insecticides are strictly followed.
  7. Proper communication and education of the population will help to increase acceptability of IRS operation; people have to know that re-plastering of houses before three to six months would make IRS ineffective.
  8. IRS operations should be completed just before the beginning of the malaria transmission season.
  9. Quality of spray operation is very important for IRS to be effective and the quality depends on effective training of the spray operators.
  10. The community should understand that the objective of IRS is to kill the mosquitoes and protect people from malaria; it is not to kill bedbugs or other pests.
  11. You are the key person in planning and implementation of IRS in your village; ask for support from community leaders, the health centre and District Health Office whenever necessary.

Self-Assessment Questions (SAQs) for Study Session 10

Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions. Write your answers in your Study Diary and discuss them with your Tutor at the next Study Support Meeting. You can check your answers with the Notes on the Self-Assessment Questions at the end of this Module.

SAQ 10.1 (tests Learning Outcomes 10.1 and 10.2)

The resting habits of mosquitoes are very important for IRS. Which of the following sites can serve as resting places for a blood-fed mosquito, so they should be sprayed with insecticide? Which ones cannot be sprayed?

  • Walls of houses
  • Furniture in houses
  • Streams
  • Animal shelters
  • Lakes
  • Rivers
  • Latrines.
Answer

Walls of houses, animal shelters and latrines, as well as household furniture, can serve as resting places for blood-fed mosquitoes, and should be sprayed with insecticides.

Streams, lakes and rivers are not resting places for adult mosquitoes.

SAQ 10.2 (tests Learning Outcome 10.2)

Which of the following statements is false? In each case, explain what is incorrect.

A  Blood-fed mosquitoes rest on either the inside of houses or in vegetation outdoors.

B  Mosquitoes that rest outside houses after feeding are easier to control with IRS.

C  After taking a blood meal, mosquitoes have to rest about 10 days before laying their eggs and seeking their next blood meal.

D  Blood-fed mosquitoes can often rest on the outside walls of houses.

E  IRS kills mosquitoes entering houses and resting on sprayed walls and furniture.

Answer

A is true. Blood-fed mosquitoes can rest either indoors or outdoors.

B is false. Mosquitoes that rest outside houses are harder to control using IRS.

C is false. After taking a blood meal mosquitoes rest for about two days (not 10 days) before laying eggs.

D is false. Blood-fed mosquitoes do not usually rest on the outside walls of houses. They prefer shaded and undisturbed sites.

E is true. IRS only kills mosquitoes entering and/or resting in sprayed houses.

SAQ 10.3 (tests Learning Outcome 10.3)

You will be responsible for undertaking IRS in your village and before you start the operation you have to make sure you have all the resources ready. What are the items you have to request from the District Health Office, and what do you have to do at the community level?

Answer

You have to request the following items from the District Health Office:

  • Spray pumps, insecticides, spray pump spare kits, tool kits for pump maintenance, personal protective equipment.
  • At the community level you have to select and train spray operators.

SAQ 10.4 (tests Learning Outcome 10.3)

What is the capacity of the spray pump used for IRS in Ethiopia? What is the surface area that can be sprayed by one full spray pump of insecticide?

Answer
  • The spray pumps used in Ethiopia have eight litres capacity.
  • One spray pump full of insecticide can spray 200 m2 of surface area.

SAQ 10.5 (tests Learning Outcomes 10.3 and 10.5)

Your village has 800 households and the average housing unit per household is 1.5. At the end of your spray operation, your record shows that 900 housing units were sprayed and the rest were unsprayed.

  • a.How many housing units were expected to be sprayed?
  • b.How many housing units were unsprayed?
  • c.What is the coverage of this IRS operation? Express you answer as % of housing units sprayed.
  • d.Is the coverage of this IRS operation acceptable? Say why or why not.
Answer
  • a.800 households multiplied by 1.5 housing units per household = 1,200 housing units.
  • b.900 housing units were sprayed. Therefore 1,200 – 900 = 300 housing units were unsprayed.
  • c.The coverage of this IRS operation is (900/1,200) x 100 = 75%.
  • d.The coverage is not acceptable; the minimum coverage acceptable for IRS to be effective is 85%.

Read Case Study 10.1 carefully and then answer the questions below it.

Case Study 10.1  A village IRS programme

Your village has 500 households and each household has two housing units. One spray operator sprays 20 housing units per day. You have five spray operators with five spray pumps to undertake the operation. The average surface area of one housing unit is 100 m2. From Section 10.5 you have learned that one spray pump of insecticide (one sachet) covers 200 m2 surface area.

SAQ 10.6 (tests Learning Outcomes 10.3 and 10.5)

  • a.How many working days will be needed to spray the entire village?
  • b.How many sachets of insecticide do you need for the village?
  • c.How many sachets does one spray operator need to carry for one day’s work?

In each case, explain how you arrived at your answer.

Answer
  • a.Ten days. This is worked out as follows: there are 500 x 2 = 1,000 housing units. Number of units 5 spray operators can spray in one day = 5 (spray operators) x 20 (units each operator sprays in a day) = 100 units. So the number of days to spray the entire village of 1,000 units at 100 units per day = 10 days.
  • b.Five hundred sachets. This is worked out as follows: one sachet sprays 200 m2 which is equal to 2 housing units. 1,000 housing units divided by 2 units per sachet = 500 sachets.
  • c.Ten sachets. This is worked out as follows: one spray operator sprays 20 housing units per day. One sachet is needed to spray 200 m2 surface area, which is enough for 2 housing units of 100 m2 each. To spray 20 housing units at 2 housing units per sachet = 10 sachets.

SAQ 10.7 (tests Learning Outcome 10.6)

Which of the following statements about the safe handling of insecticides is false? In each case, explain what is incorrect.

A  Spray operators need to wear a shirt and trousers during spraying.

B  Hands and faces should be washed with soap after spraying, and before eating or drinking.

C  Any leftover insecticide should be poured into rivers.

D  Spray operators can keep wearing contaminated clothes for a week without washing.

Answer

A is false. Shirts and trousers do not give enough protection. Spray operators also need to wear a hat, mask, goggles and gloves etc. to protect themselves from contamination.

B is true. Hands and faces should be washed with soap after spraying and before eating or drinking

C is false. Any leftover insecticides should be disposed of in a pit prepared for this purpose; they should never be poured into a river (or other water body).

D is false. Contaminated clothes have to be changed and washed immediately.