It was long accepted that weather-related problems were a natural phenomenon and death and injury from such events were inevitable (see table 1). It is only in the past two decades that we have begun to look at factors contributing to weather-related death and injury as a means of prevention. Because of the short duration of study in this area, the data are limited, particularly as they pertain to the number and circumstances of weather-related deaths and injuries among workers. The following is an overview of the findings thus far.

Table 1. Weather-related occupational risks

*degree of risk.

Floods, Tidal Waves

Definitions, sources and occurrences

Flooding results from a variety of causes. Within a given climatic region, tremendous variations of flooding occur because of fluctuations within the hydrological cycle and other natural and synthetic conditions (Chagnon, Schict and Semorin 1983). The US National Weather Service has defined flash floods as those that follow within a few hours of heavy or excessive rain, a dam or levee failure or a sudden release of water impounded by an ice or log jam. Although most flash floods are the result of intense local thunderstorm activity, some occur in conjunction with tropical cyclones. Forerunners to flash floods usually involve atmospheric conditions that influence the continuation and intensity of rainfall. Other factors that contribute to flash floods include steepness of slopes (mountain terrain), absence of vegetation, lack of infiltration capability of the soil, floating debris and ice jams, rapid snow melt, dam and levee failures, rupture of a glacial lake, and volcanic disturbances (Marrero 1979). River flooding can be influenced by factors which cause flash flooding, but more insidious flooding may be caused by stream channel characteristics, character of soil and subsoil, and degree of synthetic modification along its path (Chagnon, Schict and Semorin 1983; Marrero 1979). Coastal flooding can result from storm surge, which is the result of a tropical storm or cyclone, or ocean waters driven inland by wind-generated storms. The most devastating type of coastal flooding is the tsunami, or tidal wave, which is generated by submarine earthquakes or certain volcanic eruptions. Most recorded tsunamis have occurred in the Pacific and Pacific coast regions. The islands of Hawaii are particularly prone to tsunami damage because of their location in the mid-Pacific (Chagnon, Schict and Semorin 1983; Whitlow 1979).

Factors influencing morbidity and mortality

It has been estimated that floods account for 40% of all the world’s disasters, and they do the greatest amount of damage. The most lethal flood in recorded history struck the Yellow River in 1887, when the river overflowed 70-foot-high levees, destroying 11 cities and 300 villages. An estimated 900,000 people were killed. Several hundred thousand may have died in China’s Shantung Province in 1969 when storm surges pushed flood tides up the Yellow River Valley. A sudden flood in January 1967 in Rio de Janeiro killed 1,500 people. In 1974 heavy rains flooded Bangladesh and caused 2,500 deaths. In 1963 heavy rains caused an enormous landslide that fell into the lake behind the Vaiont Dam in Northern Italy, sending 100 million tons of water over the dam and causing 2,075 deaths (Frazier 1979). In 1985 an estimated 7 to 15 inches of rain fell in a ten-hour period in Puerto Rico, killing 180 people (French and Holt 1989).

River flooding has been curtailed by engineering controls and increased forestation of watersheds (Frazier 1979). However, flash floods have increased in recent years, and are the number one weather-related killer in the United States. The increased toll from flash floods is attributed to increased and more urbanized populations on sites that are ready targets for flash floods (Mogil, Monro and Groper 1978). Fast-flowing water accompanied by such debris as boulders and fallen trees account for the primary flood-related morbidity and mortality. In the United States studies have shown a high proportion of car-related drownings in floods, due to people driving into low-lying areas or across a flooded bridge. Their cars may stall in high water or be blocked by debris, trapping them in their cars while high levels of fast-flowing water descend upon them (French et al. 1983). Follow-up studies of flood victims show a consistent pattern of psychological problems up to five years after the flood (Melick 1976; Logue 1972). Other studies have shown a significant increase in the incidence of hypertension, cardiovascular disease, lymphoma and leukaemia in flood victims, which some investigators feel are stress related (Logue and Hansen 1980; Janerich et al. 1981; Greene 1954). There is a potential for increased exposure to biological and chemical agents when floods cause disruption of water purification and sewage-disposal systems, rupture of underground storage tanks, overflowing of toxic waste sites, enhancement of vector-breeding conditions and dislodgement of chemicals stored above ground (French and Holt 1989).

Although, in general, workers are exposed to the same flood-related risks as the general population, some occupational groups are at higher risk. Clean-up workers are at high risk of exposure to biological and chemical agents following floods. Underground workers, particularly those in confined places, may be trapped during flash floods. Truck drivers and other transportation workers are at high risk from vehicle-related flood mortality. As in other weather-related disasters, fire-fighters, police and emergency medical personnel are also at high risk.

Prevention and control measures and research needs

Prevention of death and injury from floods can be accomplished by identifying flood-prone areas, making the public aware of these areas and advising them on appropriate prevention actions, conducting dam inspections and issuing dam safety certification, identifying meteorological conditions that will contribute to heavy precipitation and runoff, and issuing early warnings of floods for a specific geographic area within a specific time frame. Morbidity and mortality from secondary exposures can be prevented by assuring that water and food supplies are safe to consume and are not contaminated with biological and chemical agents, and by instituting safe human waste disposal practices. Soil surrounding toxic waste sites and storage lagoons should be inspected to determine if there has been contamination from overflowing storage areas (French and Holt 1989). Although mass vaccination programmes are counterproductive, clean-up and sanitation workers should be properly immunized and instructed in appropriate hygienic practices.

There is a need to improve technology so that early warnings for flash floods can be more specific in terms of time and place. Conditions should be assessed to determine whether evacuation should be by car or on foot. Following a flood a cohort of workers engaged in flood-related activities should be studied to assess the risk of adverse physical and mental health effects.

Hurricanes, Cyclones, Tropical Storms

Definitions, sources and occurrences

A hurricane is defined as a rotating wind system that whirls counterclockwise in the northern hemisphere, forms over tropical water, and has sustained wind speeds of at least 74 miles per hour (118.4 km/h). This whirling accumulation of energy is formed when circumstances involving heat and pressure nourish and nudge the winds over a large area of ocean to wrap themselves around an atmospheric low-pressure zone. A typhoon is comparable to a hurricane except that it forms over Pacific waters. Tropical cyclone is the term for all wind circulations rotating around an atmospheric low over tropical waters. A tropical storm is defined as a cyclone with winds from 39 to 73 mph (62.4 to 117.8 km/h), and a tropical depression is a cyclone with winds less than 39 mph (62.4 km/h).

It is presently thought that many tropical cyclones originate over Africa, in the region just south of the Sahara. They start as an instability in a narrow east to west jet stream that forms in that area between June and December, as a result of the great temperature contrast between the hot desert and the cooler, more humid region to the south. Studies show that the disturbances generated over Africa have long lifetimes, and many of them cross the Atlantic (Herbert and Taylor 1979). In the 20th century an average of ten tropical cyclones each year whirl out across the Atlantic; six of these become hurricanes. As the hurricane (or typhoon) reaches its peak intensity, air currents formed by the Bermuda or Pacific high-pressure areas shift its course northward. Here the ocean waters are cooler. There is less evaporation, less water vapour and energy to feed the storm. If the storm hits land, the supply of water vapour is cut off entirely. As the hurricane or typhoon continues to move north, its winds begin to diminish. Topographical features such as mountains may also contribute to the breakup of the storm. The geographic areas at greatest risk for hurricanes are the Caribbean, Mexico, and the eastern seaboard and Gulf Coast states of the United States. A typical Pacific typhoon forms in the warm tropical waters east of the Philippines. It may move westward and strike the Chinese mainland or veer to the north and approach Japan. The storm’s path is determined as it moves around the western edge of the Pacific high-pressure system (Understanding Science and Nature: Weather and Climate 1992).

The destructive power of a hurricane (typhoon) is determined by the way storm surge, wind and other factors are combined. Forecasters have developed a five-category disaster potential scale to make the predicted hazards of approaching hurricanes clearer. Category 1 is a minimum hurricane, category 5 a maximum hurricane. In the period 1900-1982, 136 hurricanes struck the United States directly; 55 of these were of at least category 3 intensity. Florida felt the effects of both the highest number and the most intense of these storms, with Texas, Louisiana and North Carolina following in descending order (Herbert and Taylor 1979).

Factors influencing morbidity and mortality

Although winds do much damage to property, the wind is not the biggest killer in a hurricane. Most victims die from drowning. The flooding that accompanies a hurricane may come from the intense rain or from the storm surges. The US National Weather Service estimates that storm surges cause nine of every ten hurricane-associated fatalities (Herbert and Taylor 1979). The occupational groups most heavily impacted by hurricanes (typhoons) are those related to boating and shipping (which would be affected by the unusually rough seas and high winds); utility line workers who are called into service to repair damaged lines, often while the storm is still raging; fire-fighters and police officers, who are involved in evacuations and protecting the property of evacuees; and emergency medical personnel. Other occupational groups are discussed in the section on floods.

Prevention and control, research needs

The incidence of deaths and injuries associated with hurricanes (typhoons) has dropped dramatically in the past twenty years in those areas where sophisticated advanced warning systems have been put into effect. The principal steps to follow for preventing death and injury are: to identify meteorological precursors of these storms and track their course and potential development into hurricanes, to issue early warnings to provide for timely evacuation when indicated, to enforce stringent land use management practices and building codes in high-risk areas, and to develop emergency contingency plans in high-risk areas to provide for an orderly evacuation and adequate shelter capacity for evacuees.

Because the meteorological factors contributing to hurricanes have been well studied, a good deal of information is available. More information is needed on the variable pattern of incidence and intensity of hurricanes over time. The effectiveness of existing contingency plans should be assessed following each hurricane, and it should be determined if buildings protected from wind speed are also protected from storm surges.

Tornadoes

Formation and patterns of occurrence

Tornadoes are formed when layers of air of different temperature, density and windflow combine to produce powerful updrafts forming huge cumulonimbus clouds which are transformed into rotating tight spirals when strong cross winds blow through the cumulonimbus cloud. This vortex draws even more warm air into the cloud, which makes the air spin faster until a funnel cloud packing explosive force drops out of the cloud (Understanding Science and Nature: Weather and Climate 1992). The average tornado has a track approximately 2 miles long and 50 yards wide, affecting about 0.06 square miles and with wind speeds as high as 300 mph. Tornadoes occur in those areas where warm and cold fronts are apt to collide, causing unstable conditions. Although the probability that a tornado will strike any specific location is extremely small (probability 0.0363), some areas, such as the Midwest states in the United States, are particularly vulnerable.

Factors influencing morbidity and mortality

Studies have shown that people in mobile homes and in lightweight cars when tornadoes strike are at particularly high risk. In the Wichita Falls, Texas, Tornado Study, occupants of mobile homes were 40 times more likely to sustain a serious or fatal injury than those in permanent dwellings, and occupants of automobiles were at approximately five times greater risk (Glass, Craven and Bregman 1980). The leading cause of death are craniocerebral trauma, followed by crushing wounds of the head and trunk. Fractures are the most frequent form of non-fatal injury (Mandlebaum, Nahrwold and Boyer 1966; High et al. 1956). Those workers who spend a major part of their working time in lightweight automobiles, or whose offices are in mobile homes, would be at high risk. Other factors relating to clean-up operators discussed in the flood section would apply here.

Prevention and control

The issuing of appropriate warnings, and the need for the population to take appropriate action on the basis of those warnings, are the most important factors in preventing tornado-related death and injury. In the United States, the National Weather Service has acquired sophisticated instrumentation, such as Doppler radar, which permits them to identify conditions conducive to the formation of a tornado and to issue warnings. A tornado watch means that conditions are conducive to tornado formation in a given area, and a tornado warning means that a tornado has been sighted in a given area and those residing in that area should take appropriate shelter, which entails going to the basement if one exists, going to an inside room or closet, or if outside, going to a ditch or gully.

Research is needed to assess whether warnings are effectively disseminated and the extent to which people heed those warnings. It should also be determined whether the prescribed shelter areas really provide adequate protection from death and injury. Information should be gathered on the number of deaths and injuries to tornado workers.

Lightning and Forest Fires

Definitions, sources and occurrences

When a cumulonimbus cloud grows into a thunderstorm, different sections of the cloud accumulate positive and negative electric charges. When the charges have built up, the negative charges flow toward the positive charges in a lightning flash that travels within the cloud or between the cloud and the ground. Most lightning travels from cloud to cloud, but 20% travels from cloud to ground.

A lightning flash between a cloud and the ground can be either positive or negative. Positive lightning is more powerful and is more likely to start forest fires. A lightning strike will not start a fire unless it meets easily ignitable fuel like pine needles, grass and pitch. If the fire hits decaying wood, it can burn unnoticed for a long period of time. Lightning ignites fires more often when it touches the ground and the rain within the thunder cloud evaporates before it reaches the ground. This is called dry lightning (Fuller 1991). It is estimated that in dry, rural areas such as Australia and the western United States, 60% of forest fires are caused by lightning.

Factors causing morbidity and mortality

Most of the fire-fighters who die in a fire die in truck or helicopter accidents or from being hit by falling snags, rather than from the fire itself. However, fighting fire can cause heat stroke, heat exhaustion and dehydration. Heat stroke, caused by the body temperature rising to over 39.4°C, can cause death or brain damage. Carbon monoxide is also a threat, particularly in smouldering fires. In one test, researchers found that the blood of 62 of 293 fire-fighters had carboxyhaemoglobin levels above the maximum allowable level of 5% after eight hours on the fire line (Fuller 1991).

Prevention, control and research needs

Because of the danger and the mental and physical stress associated with fire-fighting, crews should not work for more than 21 days, and must have one day off for every 7 days worked within that time. In addition to wearing appropriate protective gear, fire-fighters must learn safety factors such as planning safety routes, keeping in communication, watching for hazards, keeping track of the weather, making sure of directions and acting before a situation becomes critical. The standard fire-fighting orders emphasize knowing what the fire is doing, posting lookouts and giving clear, understandable instructions (Fuller 1991).

Factors relating to prevention of lightning forest fires include limiting fuels such as dry underbrush or fire-susceptible trees like eucalyptus, preventing building in fire-prone areas and early detection of forest fires. Early detection has been enhanced by the development of new technology such as an infrared system which is mounted on helicopters to check whether lightning strikes reported from aerial lookout and detection systems have actually started fires and to map hot spots for ground crews and helicopter drops (Fuller 1991).

More information is needed on the number and circumstances of deaths and injuries associated with lightning-related forest fires.

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