There is a perception that many of the substances found in carpet are transferred to air or directly to humans, and that carpet is the causal source of adverse effect, for example, allergic reaction and asthma attack. The benefits of carpet are forgotten or ignored in the face of perceived hazards. Some common hazard perceptions include:
“Allergen ridden carpet triggers asthma.”
“Carpet is a repository for carcinogens or poisons which can be inhaled or ingested by humans.”
“Walking over carpet releases fine particles to the indoor atmosphere.”
“VOC released from carpet triggers chemical sensitivities.”
The benefits of carpet are often abandoned by the removal of carpet based on the perception of risks and adverse effects. The following is an application of the risk assessment paradigm to analyze possible human response to carpet in a dynamic built environment.
Risk is the probability of an adverse effect. The effect can be seen in response of a living (human, animal) receptor or damage to a valuable material. A discussion of risk from exposure to carpet must begin by assuming humans are exposed to heavily loaded carpet. A carpet free of matter poses zero risk to public health.
Keeping in mind that matter transfers out of a compartment in proportion to the amount of matter in the compartment, carpet with a loading of less than 1gm/m2 is for all practical purposes “sanitary.” However, carpet with loading greater that 2gm/m2 is more likely to release matter to the surrounding environment, elevate exposure and risk.
As a primary source of risk, carpet has been assessed in terms of its VOC and man-made mineral fiber (MMMF) emissions. Carpet is also perceived as the primary habitat for living organisms: fungi, mite, and bacteria.
Carpet as an environmental compartment stores a variety of hazardous substances that originate outside the carpet compartment. The primary risk concern is how much of the substance is transferred from carpet in a manner and quantity so as to adversely affect a human receptor. This suggests that carpet is primarily a “secondary” source of risk.
A carpet free of matter poses zero risk to public health.
VOC, MMMF, highly dense mineral or organic particulate matter, oils, viruses do not become re-suspended (airborne) and have little probability of causing an adverse affect by way of dermal exposure. Ingestion of such substances has little potential to cause an adverse effect. Very fine particles (<1um) do not have a tendency to become reentrained once in carpet. They are judged to be very low risk in term of carpet exposure.
There is some low to moderate risk of adverse response associated with the direct contact (dermal and subsequent ingestion) associated with useful poisons (pesticides), heavy metals, bacteria and mycotoxin (metabolites of fungi). These risks can be greatly reduced through the cleaning process.
Some of the substances found in carpet are classified as allergens. This category of substances has the greatest potential to be reentrained to air. Entrainment potential as mentioned previously is a function of loading. The greater the loading, the more likely the entrainment.
An allergen is any substance that causes a hypersensitive reaction. In healthy humans, most allergic reactions are prevented by the immune system. However after a significant exposure to a particular allergen, an individual who develops an allergy becomes sensitized to that allergen. Sensitization occurs when the antibody specific for the allergen attaches to the surface of the mast cells making the individual react to future exposures. Subsequent exposures cause the release of agents that interact with surrounding tissue.
The health literature indicates that respiratory allergies are triggered when an airborne allergen reaches the mucus membranes that line the inside of the cranial cavity. People with allergies experience sneezing; nasal congestion; wheezing; coughing; post nasal drip; itching eyes, noise, and throat; dark cycles under eyes; watering eyes; and conjunctivitis. In very rare but severe case, allergic reactions can include feeling faint; rapid pulse; difficulty breathing; nausea and vomiting; stomach pain; hives; swelling of the lips tongue and throat; drowsiness, confusion, or loss of consciousness.
These health effects are generally not life threatening but detract from an overall sense of well-being and often interfere with human productivity important in environments like offices and schools.
Particles in the range >10um are those that most cause allergic reactions. These large size particles irritate mucus membrane in the cranial cavity. The pulmonary system’s natural defense mechanism usually clears the lungs of particles greater than 10um.
The most common airborne allergens include pollen from trees, grasses, and weed; molds and yeasts, the two groups of organisms in the fungi family; “household dust” that contains a variety of spores, food particles, parts of plants and insects, dust mites and their waste products; animal dander (saliva) from household cats and dogs; tobacco smoke, and various VOCs (gas phase organic chemicals).
By and large these substances are allergens: fungi, mite, cockroach, cat and dog. Of these allergens, cat and dog pose the most common risk. The good news here is that these primary sources can be kept outside.
Most important to a proper understanding of health response to allergens is the principle, “It’s the dose that makes the poison.” We need a sufficiently high dose of allergen spores delivered to a human before we can have an effect.
Periodic vacuuming keeps concentrations of allergens at levels where they tend to not to cause reactions.
(The views and opinions of the author or originators expressed herein do not necessarily state or reflect those of HFI: its principals, executives, board members, advisors or affiliates.)
Environmental Risk Assessment Framework—Heavily Loaded Carpet
| Substances in Heavily Loaded Carpet | Hazard Identification | Source and Transport Analysis | Exposure/ Response Analysis | Human Risk Characterization (carpet exposure) |
| Heavy soils and PM (>20um) | Damage to materials | Tracking from outside | Minimal | N/A |
| Ambient Air Dusts (1-15um) | Allergic response | Gravitational settling | Low-Moderate-High | Low-Moderate |
| Ambient Air Dust (fine <1um) | Allergic response | Gravitational settling, impaction | Low | Low |
| Indoor Air Dusts (1-15um <1um) | Allergic response, SBS | Breakage | Low-Moderate | Low-Moderate |
| Indoor Air Dusts (fine) | Allergic response | PIC | Low-Moderate | Low |
| Toxic PM (eg. heavy metals) | Cancer | Tracking from outside. Indoor settling | Ingestion-child | Low |
| Fibers (e.g., asbestos, MMMF) | Cancer | Indoor settling | Low | Low |
| HC (oils) | Damage to materials | Tracking from outside | Low-Moderate | N/A-Low |
| Chemical/Pesticide | Cancer, MCS | Tracking from outside. Indoor application | Low | Low |
| VOC (gas phase organic compounds) | SBS | Indoor emissions | Minimal | Minimal |
| Allergens | ||||
| Pollen | Allergic reaction | Ambient air | Low | Low |
| Fungi | Allergic reaction | Ambient air | Low-Moderate | Low-Moderate |
| (1,3 B Glucans) | Fungi marker | |||
| Mite | Allergic reaction | Indoor surfaces | Moderate | Low-Moderate |
| Cockroach | Allergic reaction | Indoor surfaces | Moderate | Low-Moderate |
| Cat and Dog | Allergic reaction | Indoor air | Moderate-High | Moderate-High |
| Infectious Agents | ||||
| Bacteria | Infectious disease | Natural decomposition | Low-Moderate | Low-Moderate |
| (Endotoxin) | Bacteria marker | |||
| Viruses | Infectious disease | Infected living host | Minimal | Minimal |
