Dichloromethane, usually called methylene chloride, is the lightest and most volatile of the common chlorinated solvents. Under the WHO and ISO volatility convention it falls into the very volatile organic compound class, whose members boil below about 50 to 100 °C — a classification with real consequences for how it must be sampled. It is an episodic contaminant tied to an activity, not a background emitter from building fabric.
Dichloromethane, usually called methylene chloride, is the lightest and most volatile of the common chlorinated solvents. Under the WHO and ISO volatility convention it falls into the very volatile organic compound class, whose members boil below about 50 to 100 °C — a classification with real consequences for how it must be sampled.
That volatility is the defining feature. Dichloromethane evaporates extremely quickly from an open container or a treated surface, so a short task can produce a high, rapidly changing concentration in a small room and then decay quickly once the work stops. It is an episodic contaminant tied to an activity, not a background emitter from building fabric: gypsum board, joinery, flooring and decorative paint do not release it.
The practical consequence is that timing dominates. A survey carried out on a day when no stripping or degreasing work is under way may return nothing at all in a space where occupants have genuine complaints.
Where stripping or degreasing is carried out regularly, extraction at the work position is the control that keeps that peak out of the room, and the annual testing, inspection and record-keeping duties attached to such systems in the Emirate of Abu Dhabi are described in Adhesives, Sealants and Solvents.
Paint strippers and graffiti removers are the most significant source. Dichloromethane-based strippers remain in use for removing cured coatings from metal, masonry and joinery, and graffiti and adhesive-residue removers based on it are used in car parks, service cores and back-of-house corridors. These are maintenance tasks carried out inside occupied buildings, often in enclosed spaces such as stair cores, plant rooms and basement levels where ventilation is designed for heat removal rather than solvent dilution.
Some adhesives and aerosol formulations also contain it — contact adhesives, certain spray products, mould-release and lubricant aerosols, and some specialist cleaning sprays used in fit-out and maintenance. In the UAE's high-volume fit-out sector an aerosol used on one floor can affect another through a shared riser or air-handling zone.
Degreasing is the third route. Dichloromethane is used for cleaning metal parts and equipment in workshops, maintenance bays and plant rooms. As with other chlorinated solvents, the UAE's mixed-use pattern means such an operation is frequently connected to occupied areas by a shared stair, riser or car park.
Evaporation from a solvent-wetted surface rises sharply with temperature, so the same stripping or degreasing task releases more, and releases it faster, in a warm plant room or an unconditioned podium space than it would in a temperate climate. Sealed envelopes and low outdoor-air fractions held down to limit cooling load mean that what is released is recirculated rather than dispersed, and there is no window-opening habit to fall back on through the long summer.
The pattern of construction and fit-out matters as much as the climate. A large stock of buildings is in partial occupation while remedial coating, stripping and adhesive work continues elsewhere in the same structure, placing an episodic solvent source and occupied space inside one ventilation system.
Acute exposure at task-level concentrations causes eye and airway irritation and central nervous system depression — headache, dizziness, drowsiness and impaired coordination — and in confined, poorly ventilated spaces the effects can develop quickly.
The distinctive point about dichloromethane is metabolic. It is metabolised in the body to carbon monoxide, raising carboxyhaemoglobin in the blood, so exposure produces a carbon-monoxide-like effect: headache, fatigue, nausea and reduced oxygen delivery, with the effect persisting after the exposure has ended. This has a direct practical consequence for investigations. Occupants presenting with apparent carbon monoxide symptoms, or a worker with a raised carboxyhaemoglobin reading, may have been exposed to a solvent rather than to a combustion source, so a dichloromethane task in the building is a legitimate line of enquiry when a combustion investigation finds no source. The separate page on carbon monoxide and combustion by-products indoors covers that side of the question.
The International Agency for Research on Cancer classifies dichloromethane as probably carcinogenic to humans. Most reported building complaints involve mixtures rather than a single substance, so symptoms alone cannot attribute cause. Occupants or workers with persistent symptoms should be referred to occupational health or a medical practitioner rather than to an air-testing result.
Method selection is a genuine issue for this compound rather than a formality. Because dichloromethane is a very volatile organic compound, it is poorly retained on some of the sorbents routinely packed for general volatile organic compound surveys, and it can break through the tube during sampling and be under-reported or missed entirely. Where a sorbent tube approach under EPA Compendium Method TO-17 or ISO 16000-6:2021 is used, the sorbent must be selected for the very volatile range — typically a stronger carbon-based sorbent or a multi-bed tube.
For that reason canister whole-air sampling under EPA Compendium Method TO-15A, published in 2019 and superseding TO-15, is frequently the more appropriate choice. A photoionisation detector is of limited help here: it reports a total response weighted by a response factor, does not identify compounds, and responds weakly to dichloromethane, so a low screening reading is not evidence of absence.
No UAE instrument sets a numeric indoor-air limit for dichloromethane. It is not among the substances given an individual objective in Table 4 of the Dubai Municipality guideline, and it is not among the nine pollutants covered by the WHO Guidelines for Indoor Air Quality: Selected Pollutants. In practice it is captured indirectly, as part of the total volatile organic compound figure, which does carry a Dubai Municipality value — though the sampling caveat above applies, since a result obtained on a sorbent that does not retain the compound will not include it.
Abu Dhabi does not fill the gap. The Abu Dhabi Public Health Centre's Occupational Standards and Guideline Values document — the only Abu Dhabi instrument that ever carried numeric chemical exposure limits — is recorded by ADPHC as suspended, with entities directed to comply with relevant local or federal standards in force, while Code of Practice 1.0 §3.2(c)(i) still cross-refers to it. Abu Dhabi's chemical-exposure-limit layer therefore currently points at a suspended instrument. That gap should be stated rather than filled with a value borrowed from a foreign body.
Source control is the whole of the answer here, because the source is an activity and not a material. Stripping, graffiti-removal, adhesive and degreasing tasks should be identified, and substitution with a non-chlorinated product considered first; where the task must proceed, it should be scheduled outside occupied hours, contained, and served by local extract discharging clear of any fresh-air intake.
Ventilation follows source control rather than replacing it. Additional outdoor air dilutes a concentration while the task is running but does nothing about the release itself, and in UAE summer conditions the cooling-load penalty makes it unsustainable as a permanent control. Because concentrations decay quickly once work stops, re-testing has to be planned around the activity: a sample taken during comparable work shows whether the control is effective, whereas a sample on a quiet day shows only that nothing was happening.
No UAE instrument sets a numeric indoor-air limit for dichloromethane. It is not among the substances given an individual objective in Table 4 of the Dubai Municipality guideline, and it is not among the nine pollutants covered by the WHO Guidelines for Indoor Air Quality: Selected Pollutants. In practice it is captured indirectly, as part of the total volatile organic compound figure, which does carry a Dubai Municipality value — though the sampling caveat above applies, since a result obtained on a sorbent that does not retain the compound will not include it. Abu Dhabi does not fill the gap. The Abu Dhabi Public Health Centre's Occupational Standards and Guideline Values document — the only Abu Dhabi instrument that ever carried numeric chemical exposure limits — is recorded by ADPHC as suspended, with entities directed to comply with relevant local or federal standards in force, while Code of Practice 1.0 §3.2(c)(i) still cross-refers to it. That gap should be stated rather than filled with a value borrowed from a foreign body.
There is no UAE numeric indoor-air value for dichloromethane over any averaging period. It is not given an individual objective in Table 4 of Dubai Municipality DM-HSD-GU119-IAQ Version 4 (11 December 2024) and is not among the nine pollutants in the WHO Guidelines for Indoor Air Quality: Selected Pollutants. It is captured only indirectly within the total volatile organic compound figure.
It was simply not included. Table 4 of the Dubai Municipality guideline lists a limited set of individual volatile organic compounds, and dichloromethane is not among them, nor is it one of the nine pollutants in the WHO 2010 indoor air guidelines.
The two can look alike. Dichloromethane is metabolised to carbon monoxide in the body, raising carboxyhaemoglobin and producing headache, fatigue and nausea that persist after exposure ends. Where a combustion investigation finds no source but symptoms and blood findings suggest carbon monoxide, recent solvent work in the building is worth checking.
Not necessarily. Dichloromethane is a very volatile organic compound and is poorly retained on some sorbents used for general surveys, so it can break through and be under-reported. A sorbent chosen for the very volatile range, or canister sampling under EPA Compendium Method TO-15A, should be specified.