Hawaii's Big Island was rocked early May 17, by an explosiveeruption at the Kilauea Volcano, which sent ash and debris shootingsome 30,000 feet into the air and prompted emergency officials tourge everyone near the peak to shelter in place.

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In the hours that followed, about 2,000 ash masks weredistributed to local residents, the Associated Pressreported. Residents near the fissures have been warned thatdangerously high levels of sulfur dioxide are emerging from severalvents, and vulnerable residents could be sickened.

Kīlauea is one of the most active volcanoes on Earth, and hasbeen erupting for the past 35 years. An eruption in 1924, killedone person and sent rocks, ash and dust into the air for 17days.

Since Kilauea's massive eruption May 3, flaming rivers of moltenrock have destroyed nearly 50 structures, according to the HawaiiTribune Herald.

The Hawaii Tourism Authority recently distributed aguide, ”The Health Hazards of Volcanic Ash: A guide for thepublic,” prepared by the International Volcanic Health HazardNetwork (IVHHN), Cities and Volcanoes Commission, GNS Science andthe U.S. Geological Survey, to promote safety of those whoexperience volcanic ashfall.

Volcanic ash & other eruption fallout

Volcanic ash is composed of fine particles of fragmentedvolcanic rock (less than 2 mm diameter). Volcanic ash is often hotvery close to the volcano but is cool when it falls at greaterdistances. It's formed during volcanic explosions, from avalanchesof hot rock that flow down the side of volcanoes, or from red-hotliquid lava spray.

Ash varies in appearance depending upon the type of volcano andthe form of the eruption. Thus, it can range in colour from lightgrey to black and can vary in size from being like grit to being asfine as talcum powder.

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Airborne ash blocks out sunlight, reducing visibility andsometimes causes complete darkness during day light.

Large ash deposits can incorporate into existing soils andbecome the future topsoil of a volcanic region. The fertility ofthe soils around many volcanoes is due to old ash deposits. Thisbeneficial effect of volcanism outweighs, over time, thehazards from infrequent eruptions, so fertile volcanic areasare often densely populated

Damage caused by ash

Freshly fallen ash particles can have acid coatings which maycause irritation to the lungs and eyes. This acid coating israpidly removed by rain, which may then pollute local watersupplies. Acidic ash can also damage vegetation, leading to cropfailure.

In most eruptions, volcanic ash causes relatively few healthproblems, but generates much anxiety. People can be more fearful ofthe health hazards of volcanic ash and gases than of the risk ofdying from more major hazards, such as pyroclastic flows. However,ashfalls can affect very wide areas around volcanoes and may causemajor disruption to normal living.

Above is a slideshow of the top health and property impacts oflarge ashfalls.

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Human health is always a major concern during volcanoeruptions.

Common respiratory symptoms of volcanic ash exposure

• Nasal irritation and discharge (runny nose).
  Throat irritation and sore throat, sometimes accompanied bydry coughing.
• People with pre-existing chest complaints may develop severebronchitic symptoms which last some days beyond exposure to ash(for example, hacking cough, production
  of sputum, wheezing, or shortness of breath).
• Airway irritation for people with asthma or bronchitis; commoncomplaints of people with asthma include shortness of breath,wheezing and coughing.
• Breathing becomes uncomfortable.

In rare circumstances, long-term exposure to fine volcanic ashmay lead to serious lung diseases. For these diseases to occur, theash must be very fine, contain crystalline silica (for the diseasesilicosis to occur) and the people must be exposed to the ash inhigh concentrations over many years.

Exposure to crystalline silica in volcanic ash is typicallyof short duration (days to weeks), and studies suggest that therecommended exposure limits (similar in most countries) can beexceeded for short periods of time for the general population.

People suffering from asthma or other lung problems such asbronchitis and emphysema, and severe heart problems are most atrisk.

Factors that impact respiratory symptoms

The development of respiratory symptoms from the inhalation ofvolcanic ash depends on a number of factors. These include the:

• Concentration of particles in the air.
• Proportion of fine particles in the ash.
• Frequency and duration of exposure.
• Presence of crystalline silica and volcanic gases or aerosolsmixed with the ash.
• Meteorological conditions.
• Existing health conditions and the use of respiratoryprotective equipment will also influence the symptomsexperienced.